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Research Update 1

By Marie Conley Smith

I n a world full of opportunities, stressors, inequalities, and distractions, maintaining a healthy lifestyle can be challenging, and sleep is often the first habit to suffer. Good sleep hygiene is a huge commitment: it takes up about a third of the day, every day, and works best when kept on a consistent schedule. It does not help that the primary short-term symptoms of insufficient sleep can be self-medicated away with caffeine. However, the effects of sleep loss can range from inconvenient to downright dangerous; people have trouble learning and being productive, take risks more readily, and are more likely to get into accidents. These effects also last longer than it takes to get them, as recovering from each night of poor sleep takes multiple days. When it comes to sleep, every night counts. In this update, we will discuss what Stanford researchers have to say about sleep and why we need it, who is getting too little of it, and some of the latest findings that may help us sleep better.

We have not cracked the code on sleep

Despite this progress, scientists have not been able to crack the code of why sleep is critical to brain function. There is also little consensus about how sleep stages actually affect quality of sleep and how they affect us when we are awake.

Part of the challenge of cracking the code on sleep is how difficult it is to study. The gold standard of sleep study, polysomnography, developed by Dement in the 1960s, 1 is the most reliable tool for measuring many sleep characteristics and detecting sleep disorders such as obstructive sleep apnea and narcolepsy. However, it is expensive and time-consuming to run, which means that usually only a night or two is recorded. This snapshot of sleep may not reflect what normally occurs for a given person, and makes it difficult to draw conclusions about their behavior and performance in the days surrounding the sleep measurement.

The recent explosion in consumer wearable devices is a promising trend for researchers because of their potential to measure thousands of people’s sleep in their natural environments. They have not yet been widely adopted as measurement tools by scientists, however, as it is unclear if they provide the level of precision and measurement consistency required for a scientific study. Researchers at Stanford have called for these devices to be cleared by the FDA before using them to assign a diagnosis. 2 The “holy grail” would be a wearable device that could track sleep accurately while also providing performance information about the rest of the day, which would allow researchers to recognize more nuanced relationships between how people sleep and how it affects their lives.

The short- and long-term effects of insufficient sleep

We all know anecdotally what it is like to get too little sleep; it might be described with words and phrases like “tired,” “cranky,” “sluggish,” and “need caffeine.” Review of the scientific literature reveals how wide-ranging these effects can be. With too little sleep, people have a harder time learning 3 and concentrating, and are more likely to take risks. 4,5 The likelihood of getting into an auto accident increases. 6 Sleep deprivation has a bidirectional relationship with depression, 7,8 in that insomnia often both precedes and follows a depressive episode. Short sleep also interferes with other Healthy Living behaviors: people are more likely to crave sweet and fatty foods 9 and to choose foods that are calorically dense, 10 are more prone to injury during exercise, 11 and have an increased risk of obesity. 12

Sleep deprivation can even affect mundane daily activities. In 2017, then Stanford PhD candidate Tim Althoff and Professor Jamie Zeitzer of the Stanford Center for Sleep Sciences and Medicine took up the sleep measurement challenge by collaborating with Microsoft Research to examine the effects of sleep deprivation through a common daily activity: using an online search engine. 13 They paired users’ Microsoft Band sleep data with their Bing searches among users who had agreed to share their activity for study. By linking quantity and timing of sleep with typing speed during the searches, they were able to draw a number of conclusions about how sleep quality affects performance.

In this study, the researchers captured the sleep duration and search engine interactions of over 31,000 people. The researchers measured the amount of time between keystrokes as people typed their search engine entries, and used this as a measure of daily performance (that is, how well people did after a night of sleep). They were able to track the people who had multiple nights of insufficient sleep (defined as 6 hours of sleep or fewer) to see if their typing speed changed. They found that, on average, one night of insufficient sleep resulted in worse performance for three days, and two nights of insufficient sleep negatively impacted performance for six days. In other words, it took people almost an entire week to recover their performance after two consecutive nights of insufficient sleep. The implication is that the impact of sleep loss can persist for days.

Recent Stanford solutions for better sleep

Ongoing research at Stanford has led both to treatments for sleep disorders and to recommendations for best sleep practices for the public.

There are a few clinics and organizations that offer CBTI remotely in an effort to give more people access. There are apps such as SleepRate , which features content designed by Stanford researchers, Somryst , which was recently approved by the FDA, and Sleepio , which is offered by several large employers as an employee benefit. The Cleveland Sleep Clinic offers a 6-week online program called “ Go! to Sleep ,” and the U.S. Department of Veterans Affairs offers one of the same duration called “ Path to Better Sleep .” A physician should be consulted before starting any of these programs to ensure there are not any underlying disorders that need to be addressed.

Ultrashort light flash therapy Professor Jamie Zeitzer was interested in helping people who had a hard time sleeping because their circadian rhythm was not in sync with their desired sleep schedule. He discovered that ultrashort bursts of light directed into a person’s closed eyes while they were sleeping was very effective at shifting the time a person starts getting sleepy. Sleep doctors had already been using continuous light to help people reset their internal clock while they were awake; this new short-flash method shows great promise not only because of its effectiveness, but because it can be administered passively while people are sleeping. The approach involves wearing a sleep mask that emits the bright flashes and has been shown to only wake individuals who are particularly sensitive to light.

Lumos Sleep Mask

Professor Zeitzer and his team administered these ultrashort light flashes to teenagers, whose natural circadian systems have shifted so that their sleep and wake times are considerably later than children or adults. The time structure of our society, and schools in particular, does not take this into account. Professor Zeitzer administered the light flashes to see if it would help teens go to bed earlier. 20 They found that, while the teenagers were getting sleepy earlier, the light flashes alone were not enough to get the teenagers to bed earlier. With a second group of teens, they combined the light therapy with cognitive behavioral therapy (CBT) sessions. The CBT sessions served to inform the teens about sleep health and hygiene and helped them schedule their activities to allow for their desired sleep hours. After this combined therapy trial, the teens went to bed an average of 50 minutes earlier, getting an average of 43 more minutes of sleep per night. The researchers found the CBT component to be integral to behavior change – without the added education and support, the teens were not motivated enough to change their behavior and would simply push past their sleepiness.

This ultrashort light flash therapy can be used by anyone who may want to shift their sleep schedule; for example, to rebound from jet lag or to cope with a consistent graveyard shift at work. There is no evidence that other groups would require accompanying CBT like the teens, as long as they are self-motivated to change their sleep schedule. Zeitzer plans to test this technology next with older adults who wish to push their sleep time later. A company has spun out of this work, which Zeitzer advises but in which he has no financial interest, called Lumos . They are currently developing their product, and are hoping to make this intervention widely available.

Data Spotlight on: Black Americans

While most Americans have seen improvements in sleep over the past decade, Black Americans continue to sleep significantly less than other groups. This trend has been examined both by researchers and the popular press. 21,22 Researchers have found that Black Americans, in addition to getting shorter sleep, are also more likely to get poor quality sleep – spending less time in the most restorative stages of sleep 23,24 – and to develop obstructive sleep apnea. 25 Black Americans are also disproportionately affected by diseases that have been associated with poor sleep, such as obesity, diabetes, 26 and cardiovascular disease. 25

The exact reason(s) for Black Americans’ poor sleep is still unclear, though researchers have proposed potential contributing factors, largely related to the social inequality Black Americans face in the U.S.:

Experiences of discrimination : the stress of racial discrimination has been associated with spending lesstime in deep sleep and more time in light sleep among Black Americans. 24

Living environment : neighborhood quality has been linked to sleep quality, 27 and Stanford researchersfound that racial and income disparities persist in neighborhoods. 28 They found that while middle-income white families are more likely to live in resource-rich neighborhoods with other middle-income families, middle-income black families tend to live in markedly lower-income, resource-poorneighborhoods.

Work and income inequality : for example, shift work can cause irregular working hours. This leadspeople to suffer “social jetlag,”; a discrepancy in sleep hours between work and free days, 29 leading tosymptoms of sleep deprivation.

Lack of access to resources : particularly sleep-related healthcare and education.

Some of these factors are being addressed directly. Professor Girardin Jean-Louis from New York University and his team have devoted themselves to addressing the access to healthcare and education issue among local black communities in New York by tailoring online materials about obstructive sleep apnea to the culture, language, and barriers of specific communities. 30 Professor Jamie Zeitzer and his team at Stanford recently completed an initial clinical trial of a drug (suvorexant), which was found to help people who work at night get three more hours of sleep during the day. 31 Professor Zeitzer’s ultrashort light flash therapy (discussed above) may also help with shift work. These interventions could help to improve sleep for Black Americans, but they may not make up the whole picture; it could be that the underlying social inequality needs to be addressed in order to fully close the sleep gap.

Thanks to Jamie Zeitzer and Ken Smith for their insights and edits on this report.

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• Pardi, D., Buman, M., Black, J., Lammers, G. J., & Zeitzer, J. M. (2017). Eating decisions based on alertness levels after a single night of sleep manipulation: A randomized clinical trial. Sleep , 40 (2). https://doi.org/10.1093/sleep/zsw039
• Chennaoui, M., Arnal, P. J., Sauvet, F., & Léger, D. (2015). Sleep and exercise: A reciprocal issue? Sleep Medicine Reviews , 20 , 59–72. https://doi.org/10.1016/j.smrv.2014.06.008
• Cappuccio, F. P., Taggart, F. M., Kandala, N. B., Currie, A., Peile, E., Stranges, S., & Miller, M. A. (2008). Meta-analysis of short sleep duration and obesity in children and adults.  Sleep ,  31 (5), 619-626.
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• Qaseem, A., Kansagara, D., Forciea, M. A., Cooke, M., & Denberg, T. D. (2016). Management of chronic insomnia disorder in adults: A clinical practice guideline from the American College of Physicians. Annals of Internal Medicine , 165 (2), 125–133. https://doi.org/10.7326/M15-2175
• Jacobs, G. D., Pace-Schott, E. F., Stickgold, R., & Otto, M. W. (2004). Cognitive behavior therapy and pharmacotherapy for insomnia: A randomized controlled trial and direct comparison. Archives of Internal Medicine , 164 (17), 1888–1896. https://doi.org/10.1001/archinte.164.17.1888
• Manber, R., Bei, B., Simpson, N., Asarnow, L., Rangel, E., Sit, A., & Lyell, D. (2019). Cognitive behavioral therapy for prenatal insomnia: A randomized controlled trial. Obstetrics & Gynecology , 133 (5), 911–919. https://doi.org/10.1097/AOG.0000000000003216
• Ong, J. C., Crawford, M. R., Dawson, S. C., Fogg, L. F., Turner, A. D., Wyatt, J. K., Crisostomo, M. I., Chhangani, B. S., Kushida, C. A., Edinger, J. D., Abbott, S. M., Malkani, R. G., Attarian, H. P., & Zee, P. C. (2020). A randomized controlled trial of CBT-I and PAP for obstructive sleep apnea and comorbid insomnia: Main outcomes from the MATRICS study. Sleep . https://doi.org/10.1093/sleep/zsaa041
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• Kaplan, K. A., Mashash, M., Williams, R., Batchelder, H., Starr-Glass, L., & Zeitzer, J. M. (2019). Effect of light flashes vs sham therapy during sleep with adjunct cognitive behavioral therapy on sleep quality among adolescents: A randomized clinical trial. JAMA Network Open , 2 (9), e1911944. https://doi.org/10.1001/jamanetworkopen.2019.11944
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• Published: 01 October 2019

Sleep quality, duration, and consistency are associated with better academic performance in college students

• Kana Okano 1 ,
• Jakub R. Kaczmarzyk 1 ,
• Neha Dave 2 ,
• John D. E. Gabrieli 1 &
• Jeffrey C. Grossman   ORCID: orcid.org/0000-0003-1281-2359 3  

npj Science of Learning volume  4 , Article number:  16 ( 2019 ) Cite this article

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Although numerous survey studies have reported connections between sleep and cognitive function, there remains a lack of quantitative data using objective measures to directly assess the association between sleep and academic performance. In this study, wearable activity trackers were distributed to 100 students in an introductory college chemistry class (88 of whom completed the study), allowing for multiple sleep measures to be correlated with in-class performance on quizzes and midterm examinations. Overall, better quality, longer duration, and greater consistency of sleep correlated with better grades. However, there was no relation between sleep measures on the single night before a test and test performance; instead, sleep duration and quality for the month and the week before a test correlated with better grades. Sleep measures accounted for nearly 25% of the variance in academic performance. These findings provide quantitative, objective evidence that better quality, longer duration, and greater consistency of sleep are strongly associated with better academic performance in college. Gender differences are discussed.

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Introduction.

The relationship between sleep and cognitive function has been a topic of interest for over a century. Well-controlled sleep studies conducted with healthy adults have shown that better sleep is associated with a myriad of superior cognitive functions, 1 , 2 , 3 , 4 , 5 , 6 including better learning and memory. 7 , 8 These effects have been found to extend beyond the laboratory setting such that self-reported sleep measures from students in the comfort of their own homes have also been found to be associated with academic performance. 9 , 10 , 11 , 12 , 13

Sleep is thought to play a crucial and specific role in memory consolidation. Although the exact mechanisms behind the relationship between sleep, memory, and neuro-plasticity are yet unknown, the general understanding is that specific synaptic connections that were active during awake-periods are strengthened during sleep, allowing for the consolidation of memory, and synaptic connections that were inactive are weakened. 5 , 14 , 15 Thus, sleep provides an essential function for memory consolidation (allowing us to remember what has been studied), which in turn is critical for successful academic performance.

Beyond the effects of sleep on memory consolidation, lack of sleep has been linked to poor attention and cognition. Well-controlled sleep deprivation studies have shown that lack of sleep not only increases fatigue and sleepiness but also worsens cognitive performance. 2 , 3 , 16 , 17 In fact, the cognitive performance of an individual who has been awake for 17 h is equivalent to that exhibited by one who has a blood alcohol concentration of 0.05%. 1 Outside of a laboratory setting, studies examining sleep in the comfort of peoples’ own homes via self-report surveys have found that persistently poor sleepers experience significantly more daytime difficulties in regards to fatigue, sleepiness, and poor cognition compared with persistently good sleepers. 18

Generally, sleep is associated with academic performance in school. Sleep deficit has been associated with lack of concentration and attention during class. 19 While a few studies report null effects, 20 , 21 most studies looking at the effects of sleep quality and duration on academic performance have linked longer and better-quality sleep with better academic performance such as school grades and study effort. 4 , 6 , 9 , 10 , 11 , 12 , 13 , 22 , 23 , 24 , 25 , 26 , 27 Similarly, sleep inconsistency plays a part in academic performance. Sleep inconsistency (sometimes called “social jet lag”) is defined by inconsistency in sleep schedule and/or duration from day to day. It is typically seen in the form of sleep debt during weekdays followed by oversleep on weekends. Sleep inconsistency tends to be greatest in adolescents and young adults who stay up late but are constrained by strict morning schedules. Adolescents who experience greater sleep inconsistency perform worse in school. 28 , 29 , 30 , 31

Although numerous studies have investigated the relationship between sleep and students’ academic performance, these studies utilized subjective measures of sleep duration and/or quality, typically in the form of self-report surveys; very few to date have used objective measures to quantify sleep duration and quality in students. One exception is a pair of linked studies that examined short-term benefits of sleep on academic performance in college. Students were incentivized with offers of extra credit if they averaged eight or more hours of sleep during final exams week in a psychology class 32 or five days leading up to the completion of a graphics studio final assignment. 33 Students who averaged eight or more hours of sleep, as measured by a wearable activity tracker, performed significantly better on their final psychology exams than students who chose not to participate or who slept less than eight hours. In contrast, for the graphics studio final assignments no difference was found in performance between students who averaged eight or more hours of sleep and those who did not get as much sleep, although sleep consistency in that case was found to be a factor.

Our aim in this study was to explore how sleep affects university students’ academic performance by objectively and ecologically tracking their sleep throughout an entire semester using Fitbit—a wearable activity tracker. Fitbit uses a combination of the wearer’s movement and heart-rate patterns to estimate the duration and quality of sleep. For instance, to determine sleep duration, the device measures the time in which the wearer has not moved, in combination with signature sleep movements such as rolling over. To determine sleep quality, the Fitbit device measures the wearer’s heart-rate variability which fluctuates during transitions between different stages of sleep. Although the specific algorithms that calculate these values are proprietary to Fitbit, they have been found to accurately estimate sleep duration and quality in normal adult sleepers without the use of research-grade sleep staging equipment. 34 By collecting quantitative sleep data over the course of the semester on nearly 100 students, we aimed to relate objective measures of sleep duration, quality, and consistency to academic performance from test to test and overall in the context of a real, large university college course.

A secondary aim was to understand gender differences in sleep and academic performance. Women outperform men in collegiate academic performance in most subjects 35 , 36 , 37 , 38 and even in online college courses. 39 Most of the research conducted to understand this female advantage in school grades has examined gender differences in self-discipline, 40 , 41 , 42 and none to date have considered gender differences in sleep as a mediating factor on school grades. There are inconsistencies in the literature on gender differences in sleep in young adults. While some studies report that females get more quantity 43 but worse quality sleep compared with males, 43 , 44 other studies report that females get better quality sleep. 45 , 46 In the current study, we aim to see whether we would observe a female advantage in grades and clarify how sleep contributes to gender differences.

Bedtime and wake-up times

On average, students went to bed at 1:54 a.m. (Median = 1:47 a.m., Standard Deviation (SD) of all bedtime samples = 2 h 11 min, SD of mean bedtime per participant = 1 h) and woke up at 9:17 a.m. (Median = 9:12 a.m., SD of all wake-up time samples = 2 h 2 min; SD of mean wake-up time per participant = 54 min). The data were confirmed to have Gaussian distribution using the Shapiro–Wilks normality test. We conducted an ANOVA with the overall score (sum of all grade-relevant quizzes and exams—see “Procedure”) as the dependent variable and bedtime (before or after median) and wake-up time (before or after median) as the independent variables. We found a main effect of bedtime ( F (1, 82) = 6.45, p  = 0.01), such that participants who went to bed before median bedtime had significantly higher overall score ( X  = 77.25%, SD = 13.71%) compared with participants who went to bed after median bedtime ( X  = 70.68%, SD = 11.01%). We also found a main effect of wake-up time ( F (1, 82) = 6.43, p  = 0.01), such that participants who woke up before median wake-up time had significantly higher overall score ( X  = 78.28%, SD = 9.33%) compared with participants who woke up after median wake-up time ( X  = 69.63%, SD = 14.38%), but found no interaction between bedtime and wake-up time ( F (1, 82) = 0.66, p  = 0.42).

A Pearson’s product-moment correlation between average bedtime and overall score revealed a significant and negative correlation ( r (86) = −0.45, p  < 0.0001), such that earlier average bedtime was associated with a higher overall score. There was a significant and negative correlation between average wake-up time and overall score ( r (86) = −0.35, p  < 0.001), such that earlier average wake-up time was associated with a higher overall score. There was also a significant and positive correlation between average bedtime and average wake-up time (r (86) = 0.68, p  < 0.0001), such that students who went to bed earlier tended to also wake up earlier.

Sleep duration, quality, and consistency in relation to academic performance

Overall, the mean duration of sleep for participants throughout the entire semester was 7 h 8 min (SD of all sleep samples = 1 h 48 min, SD of mean sleep duration per participant = 41 min). There was a significant positive correlation between mean sleep duration throughout the semester (sleep duration) and overall score ( r (86) = 0.38, p  < 0.0005), indicating that a greater amount of sleep was associated with a higher overall score (Fig. 1a ). Similarly, there was a significant positive correlation between mean sleep quality throughout the semester (Sleep Quality) and Overall Score ( r (86) = 0.44, p  < 0.00005). Sleep inconsistency was defined for each participant as the standard deviation of the participant’s daily sleep duration in minutes so that a larger standard deviation indicated greater sleep inconsistency. There was a significant negative correlation between sleep inconsistency and overall score ( r (86) = −0.36, p   <  0.001), indicating that the greater inconsistency in sleep duration was associated with a lower overall score (Fig. 1b ).

Correlations between sleep measures and overall score. a Average daily hours slept (sleep duration) vs. overall score for the semester. b Standard deviation of average daily hours of sleep (sleep inconsistency) vs. overall score in class

Timing of sleep and its relation to academic performance

To understand sleep and its potential role in memory consolidation, we examined the timing of sleep as it related to specific assessments. All Pearson correlations with three or more comparisons were corrected for multiple comparisons using false discovery rate. 47

Night before assessments

We conducted a correlation between sleep quality the night before a midterm and respective midterm scores as well as sleep duration the night before a midterm and respective scores. There were no significant correlations with sleep duration or sleep quality for all three midterms (all r s < 0.20, all p s > 0.05). Similar analyses for sleep duration and sleep quality the night before respective quizzes revealed no correlations ( r s from 0.01 to 0.26, all p s > 0.05).

Week and month leading up to assessments

To understand the effect of sleep across the time period while course content was learned for an assessment, we examined average sleep measures during the 1 month leading up to the midterms. We found a significant positive correlation between average sleep duration over the month leading up to scores on each midterm ( r s from 0.25 to 0.34, all p s < 0.02). Similar analyses for average sleep duration over one week leading up to respective quizzes were largely consistent with those of midterms, with significant correlations on 3 of 8 quizzes (rs from 0.3 to 0.4, all p s < 0.05) and marginal correlations on an additional 3 quizzes (rs from 0.25 to 0.27, all p s < 0.08).

There was a significant and positive correlation between sleep quality scores averaged over the month leading up to each midterm for all three midterms ( r s from 0.21 to 0.38, all p s < 0.05). Similar analyses for average Sleep Quality over one week leading up to respective quizzes revealed a significant correlation on 1 of 8 quizzes ( r (86) = 0.42, p  < 0.005) and marginal correlations on 3 quizzes ( r s from 0.25 to 0.27, all p s < 0.08).

Variance of assessment performance accounted for by sleep measures

In order to calculate how much of the variance on assessment performance was accounted for by the sleep measures, we conducted a stepwise regression on overall score using three regressors: sleep duration, sleep quality, and sleep inconsistency. The relative importance of each variable was calculated using the relaimpo package in R 48 to understand individual regressor’s contribution to the model, which is not always clear from the breakdown of model R 2 when regressors are correlated. We found a significant regression ( F (3,84) = 8.95, p  = .00003), with an R 2 of 0.24. Students’ predicted overall score was equal to 77.48 + 0.21 (sleep duration) + 19.59 (Sleep Quality) – 0.45 (sleep inconsistency). While sleep inconsistency was the only significant individual predictor of overall score ( p  = 0.03) in this analysis, we found that 24.44% of variance was explained by the three regressors. The relative importance of these metrics were 7.16% sleep duration, 9.68% sleep quality, and 7.6% sleep inconsistency.

Gender differences

Females had better Sleep Quality ( t (88) = 2.63, p  = 0.01), and less sleep inconsistency ( t (88) = 2.18, p  = 0.03) throughout the semester compared with males, but the two groups experienced no significant difference in sleep duration ( t (88) = 1.03, p  = 0.3). Sleep duration and sleep quality were significantly correlated in both males ( r (41) = 0.85, p  < 0.00001) and females ( r (43) = 0.64, p  < 0.00001), but this correlation was stronger in males ( Z  = −2.25, p  = 0.02) suggesting that it may be more important for males to get a long-duration sleep in order to get good quality sleep. In addition, sleep inconsistency and sleep quality were significantly negatively correlated in males ( r (41) = −0.51, p  = 0.0005) but not in females ( r (43) = 0.29, p  > 0.05), suggesting that it may be more important for males to stick to a regular daily sleep schedule in order to get good quality sleep.

Females scored higher on overall score compared with males ( t (88) = −2.48, p  = 0.01), but a one-way analysis of covariance (ANCOVA) revealed that females and males did not perform significantly different on overall score when controlling for Sleep Quality, F (1, 85) = 2.22, p  = 0.14. Sleep inconsistency and overall score were negatively correlated in males ( r (41) = −0.44, p  = 0.003) but not in females ( r (43) = −0.13, p  = 0.39), suggesting that it is important for males to stick to a regular sleep schedule in order to perform well in academic performance but less so for females. No other gender differences were detected between other sleep measures and overall score.

This study found that longer sleep duration, better sleep quality, and greater sleep consistency were associated with better academic performance. A multiple linear regression revealed that these three sleep measures accounted for 24.44% of the variance in overall grade performance. Thus, there was a substantial association between sleep and academic performance. The present results correlating overall sleep quality and duration with academic performance are well aligned with previous studies 6 , 11 , 12 , 24 , 25 on the role of sleep on cognitive performance. Similarly, this study compliments the two linked studies that found longer sleep duration during the week before final exams 47 and consistent sleep duration five days prior to a final assignment 48 enhanced students’ performance. The present study, however, significantly extends our understanding of the relation between sleep and academic performance by use of multiple objective measures of sleep throughout an entire semester and academic assessments completed along the way.

The present study also provides new insights about the timing of the relation between sleep and academic performance. Unlike a prior study, 23 we did not find that sleep duration the night before an exam was associated with better test performance. Instead we found that both longer sleep duration and better sleep quality over the full month before a midterm were more associated with better test performance. Rather than the night before a quiz or exam, it may be more important to sleep well for the duration of the time when the topics tested were taught. The implications of these findings are that, at least in the context of an academic assessment, the role of sleep is crucial during the time the content itself is learned, and simply getting good sleep the night before may not be as helpful. The outcome that better “content-relevant sleep” leads to improved performance is supported by previous controlled studies on the role of sleep in memory consolidation. 14 , 15

Consistent with some previous research 45 , 46 female students tended to experience better quality sleep and with more consistency than male students. In addition, we found that males required a longer and more regular daily sleep schedule in order to get good quality sleep. This female advantage in academic performance was eliminated once sleep patterns were statistically equated, suggesting that it may be especially important to encourage better sleep habits in male students (although such habits may be helpful for all students).

Several limitations of the present study may be noted. First, the sleep quality measures were made with proprietary algorithms. There is an evidence that the use of cardiac, respiratory, and movement information from Fitbit devices can accurately estimate sleep stages, 32 but there is no published evidence that Fitbit’s 1~10 sleep quality scores represent a valid assessment of sleep quality. Second, the relation between sleep and academic performance may be moderated by factors that can affect sleep, such as stress, anxiety, motivation, personality traits, and gender roles. Establishing a causal relation between sleep and academic performance will require experimental manipulations in randomized controlled trials, but these will be challenging to conduct in the context of real education in which students care about their grades. Third, these findings occurred for a particular student population at MIT enrolled in a particular course, and future studies will need to examine the generalizability of these findings to other types of student populations and other kinds of classes.

In sum, this study provides evidence for a strong relation between sleep and academic performance using a quantifiable and objective measures of sleep quality, duration, and consistency in the ecological context of a live classroom. Sleep quality, duration, and consistency together accounted for a substantial amount (about a quarter) of the overall variance in academic performance.

Participants

One hundred volunteers (47 females) were selected from a subset of students who volunteered among 370 students enrolled in Introduction to Solid State Chemistry at the Massachusetts Institute of Technology to participate in the study. Participants were informed of the study and gave written consent obtained in accordance with the guidelines of and approved by the MIT Committee on the Use of Humans as Experimental Subjects. Due to limitations in funding, we only had access to 100 Fitbit devices and could not enroll all students who volunteered; consequently, the first 100 participants to volunteer were selected. All participants were gifted a wearable activity tracker at the completion of the study in exchange for their participation. Seven participants were excluded from analysis because they failed to wear their activity tracker for more than 80% of the semester, three participants were excluded because they lost their wearable activity tracker, and another two participants were excluded because they completed less than 75% of the assessments in the class. Of the 88 participants who completed the study (45 females), 85 were freshmen, one was a junior and two were seniors (mean age = 18.19 years).

The Solid State Chemistry class is a single-semester class offered in the fall semester and geared toward freshmen students to satisfy MIT’s general chemistry requirement. The class consisted of weekly lectures by the professor and two weekly recitations led by 12 different teaching assistants (TAs). Each student was assigned to a specific recitation section that fit their schedule and was not allowed to attend other sections; therefore, each student had the same TA throughout the semester. Students took (1) weekly quizzes that tested knowledge on the content covered the week leading up to the quiz date, (2) three midterms that tested knowledge on the content covered in the 3–4 weeks leading up to the exam date, and (3) a final exam that tested content covered throughout the semester. Based on a one-way between subjects’ analysis of variance (ANOVA) to compare the effect of teaching assistants (TAs) on overall grade, we found no significant differences in overall grade across the TAs (F (10, 77) = 1.82, p  = 0.07. (One TA was removed from the analysis because he only had one student who was participating in this study).

Participants were asked to wear an activity tracker for the entire duration of the semester without going below 80% usage each week. If 80% or more usage was not maintained, warning emails were sent at the end of that respective week. Participants were asked to return the device if they dipped below 80% usage more than three out of the 14 weeks of the semester. The average usage rate at the end of the semester for the 88 participants who completed the study was 89.4% (SD = 5.5%). The missing data appeared to be at random and were deleted prior to data analysis. As part of a separate research question, 22 of the 88 participants joined an intense cardiovascular exercise class for which they received separate physical education credit. These students performed similarly to the other 67 participants in terms of final class grade ( t (88) = 1.57, p  = 0.12), exercise amount (total amount of moderately and very active minutes on the wearable device) (t (88) = 0.59, p  = 0.56), sleep amount ( t (88) = 0.3, p  = 0.77), and sleep quality ( t (88) = 0.14, p  = 0.9), so they were included in all of the analyses.

Participants’ activities were tracked using a Fitbit Charge HR. Data from the device were recorded as follows: heart rate every 5 min; steps taken, distance traveled, floors climbed, calories burned and activity level measurements every 15 min; resting heart rate daily; and sleep duration and quality for every instance of sleep throughout the day. Sleep quality was determined using Fitbit’s proprietary algorithm that produces a value from 0 (poor quality) to 10 (good quality).

Assessments

Nine quizzes, three midterm examinations, and one final examination were administered throughout the 14-week class to assess the students’ academic achievement. The students’ cumulative class grade was made up of 25% for all nine quizzes (lowest quiz grade was dropped from the average), 15% for each midterm exam, and 30% for the final exam for a total of 100%.

At MIT, freshmen are graded on a Pass or No Record basis in all classes taken during their first semester. Therefore, all freshmen in this class needed a C- level or better (≥50%, no grading on a curve) to pass the class. A failing grade (a D or F grade) did not go on their academic record. All upperclassmen were given letter grades; A (≥85%), B (70–84%), C (50–69%), D (45–49%), F (≤44%). Because a large portion of the class had already effectively “passed” the class before taking Quiz 9 and the final exam, we excluded these two assessments from our analyses due to concerns about students’ motivation to perform their best. We calculated for each student an overall score defined as the sum of the eight quizzes and three midterms to summarize academic performance in the course.

Reporting summary

Further information on research design is available in the Nature Research Reporting Summary linked to this article.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Code availability

No custom codes were used in the analysis of this study

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Acknowledgements

This research was supported by a grant from the Horace A. Lubin Fund in the MIT Department of Materials Science and Engineering to J.C.G. and funding from MIT Integrated Learning Initiative to K.O. and J.R.K. The authors are grateful for many useful discussions with Carrie Moore and Matthew Breen at the Department of Athletics, Physical Education, and Recreation at MIT.

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Okano, K., Kaczmarzyk, J.R., Dave, N. et al. Sleep quality, duration, and consistency are associated with better academic performance in college students. npj Sci. Learn. 4 , 16 (2019). https://doi.org/10.1038/s41539-019-0055-z

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Brain Basics: Understanding Sleep

Sleep is an important part of your daily routine—you spend about one-third of your time doing it. Quality sleep—and getting enough of it at the right times—is as essential to survival as food and water. Without sleep, you can’t form or maintain the pathways in your brain that let you learn and create new memories. Lack of sleep makes it harder to concentrate and respond quickly.

Sleep is important to a number of brain functions, including how nerve cells (neurons) communicate with each other. In fact, your brain and body stay remarkably active while you sleep. Recent findings suggest that sleep plays a housekeeping role that removes toxins in your brain that build up while you are awake.

Everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every type of tissue and system in the body—from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of health problems like high blood pressure, cardiovascular disease, diabetes, depression, and obesity.

Sleep is a complex and dynamic process that affects how you function in ways scientists are now beginning to understand. This webpage describes how your need for sleep is regulated and what happens in the brain during sleep.

Anatomy of Sleep

Several structures within the brain are involved with sleep.

The hypothalamus , a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and wakefulness.  Within the hypothalamus is the suprachiasmatic nucleus (SCN)—clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm. Some people with damage to the SCN sleep erratically throughout the day because they are not able to match their sleep/wake cycle (circadian rhythms) with the light-dark cycle. Most blind people maintain some ability to sense light to help them regulate their sleep/wake cycle.

The brainstem , which is made up of structures called the pons, medulla, and midbrain, controls the transitions between wake and sleep. Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA , reduces activity in the hypothalamus and the brainstem. The brainstem (especially the pons and medulla) also plays a special role in REM sleep. It sends signals to relax muscles essential for body posture and limb movements, so that we don’t act out our dreams.

The thalamus sends and receives information from the senses to the cerebral cortex . The cerebral cortex is the covering of the brain that has many functions, including interpreting and processing short- and long-term memory. During most stages of sleep, the thalamus becomes quiet, letting you tune out the external world. But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams. 

The pineal gland , located within the brain’s two hemispheres, receives signals from the SCN and increases production of the hormone melatonin , which helps put you to sleep once the lights go down. Scientists believe that peaks and valleys of melatonin over time are important for matching the body’s circadian rhythm to the external cycle of light and darkness.

The basal forebrain , near the front and bottom of the brain, also promotes sleep and wakefulness, while part of the midbrain acts as a system to help us stay alert during the day.  Release of a chemical called adenosine from cells helps make you feel sleepy. Caffeine counteracts sleepiness by blocking the actions of adenosine.

The amygdala , an almond-shaped structure involved in processing emotions, becomes increasingly active during REM sleep. 

Sleep Stages and Mechanisms

Sleep stages.

There are two basic types of sleep: rapid eye movement (REM) sleep and non-REM sleep. Within non-REM sleep, scientists have identified three different stages. Each is linked to specific brain waves and neuronal activity. You cycle through non-REM and REM sleep several times during a typical night, with increasingly longer, deeper REM periods occurring later in the sleep session. 

Stage 1 non-REM sleep is the changeover from wakefulness to sleep. During this short period of relatively light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches. Your brain waves begin to slow from their daytime wakefulness patterns. This stage usually lasts several minutes.   

Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep. Your heartbeat and breathing slow, and muscles relax even further. Your body temperature drops and eye movements stop. Brain wave activity slows but is marked by brief bursts of electrical activity. You spend more of your repeated sleep cycles in stage 2 sleep than in other sleep stages.

Stage 3 non-REM sleep is the period of deep sleep that you need to feel refreshed in the morning. It occurs in longer periods during the first half of the night. Your heartbeat and breathing slow to their lowest levels during sleep. Your muscles are relaxed and it may be difficult to awaken you. Brain waves become even slower.  

REM sleep first occurs about 90 minutes after falling asleep.  Your eyes move rapidly from side to side behind closed eyelids.  Mixed frequency brain wave activity becomes closer to that seen in wakefulness.  Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels. Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep. Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams.  As you age, you spend less of your time in REM sleep.  Memory consolidation most likely requires both non-REM and REM sleep.

Sleep Mechanisms

Two internal biological mechanisms —circadian rhythm and homeostasis—work together to regulate when you are awake and when you are asleep.  

Circadian rhythms direct a wide variety of functions from daily changes in wakefulness to body temperature, metabolism, and the release of hormones. They cause you to be sleepy at night and can help you wake up in the morning without an alarm. Your body’s biological clock, which is based on a 24-hour day, controls most circadian rhythms. 

Sleep-wake homeostasis keeps track of your need for sleep. Homeostasis refers to a balance between systems in the body. The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity. This sleep drive gets stronger every hour you are awake and causes you to sleep longer and more deeply after a period without sleep.

Factors that influence your sleep-wake needs include medical conditions, medications, stress, sleep environment, age, and what you eat and drink. Perhaps the greatest influence is the exposure to light.  Specialized cells in the retinas of your eyes process light and tell the brain whether it is day or night and can advance or delay our sleep-wake cycle.  Exposure to light can make it difficult to fall asleep and get back to sleep if you wake up during the night.

Night shift workers often have trouble falling asleep when they go to bed, and also have trouble staying awake at work because their natural circadian rhythm and sleep-wake cycle is disrupted. Jet lag also interferes with a person's circadian rhythms, creating a mismatch between their internal clock and the actual clock.

How Much Sleep Do You Need?

Your need for sleep and your sleep patterns change as you age, but this varies significantly across individuals of the same age. There is no magic amount of sleep that works for everybody of the same age. Babies initially sleep as much as 16 to 18 hours per day, which may boost growth and development (especially of the brain). School-age children and teens on average need about 9.5 hours of sleep per night. Most adults need 7-9 hours of sleep a night, even older people. However, older people may have more trouble getting enough sleep and are more likely to take medications that can interfere with sleep.

In general, people are getting less sleep than they need due to longer work hours and the availability of round-the-clock entertainment and other activities. 

Many people feel they can "catch up" on missed sleep during the weekend, but depending on how sleep-deprived they are, sleeping longer on the weekends may not be enough to replace the sleep they've missed.

Dreaming and Sleep Tracking

Everyone dreams.  You spend about two hours each night dreaming but may not remember most of your dreams. Its exact purpose isn’t known, but dreaming may help you process your emotions. Events from the day often invade your thoughts during sleep, and people suffering from stress or anxiety are more likely to have frightening dreams. Dreams can be experienced in all stages of sleep but usually are most vivid in REM sleep. Some people dream in color, while others only recall dreams in black and white.

Tracking Sleep Through Smart Technology

Millions of people are using smartphone apps, bedside monitors, and wearable items (including bracelets, smart watches, and headbands) to informally collect and analyze data about their sleep.  Smart technology can record sounds and movement during sleep, hours slept, and monitor heartbeat and breathing.  Using apps, data from some devices can be synced to a smartphone or tablet, or uploaded to a computer. Other apps and devices make white noise, produce light that stimulates melatonin production, and use gentle vibrations to help us sleep and wake.

The Role of Genes and Neurotransmitters

Chemical signals to sleep      .

Clusters of sleep-promoting neurons in many parts of the brain become more active as we get ready for bed. Chemicals called neurotransmitters can “switch off” or dampen the activity of cells that signal wakefulness. GABA is associated with sleep, muscle relaxation, and sedation. Norepinephrine and orexin (also called hypocretin) keep some parts of the brain active while we are awake. Other neurotransmitters that shape sleep and wakefulness include acetylcholine, histamine, adrenaline, cortisol, and serotonin.

Genes and sleep

Genes may play a significant role in how much sleep we need. Scientists have identified several genes involved with sleep and sleep disorders, including genes that control the activity of neurons, and "clock" genes such as Per , tim , and Cry, that influence our circadian rhythms and the timing of sleep. Scientists have found that different genes are linked to sleep disorders, such as sleep disorders as familial advanced sleep-phase disorder, narcolepsy, and restless legs syndrome.  Some of the genes expressed in the cerebral cortex and other brain areas change their level of expression between sleep and wake.  Several genetic models—including the worm, fruit fly, and zebrafish—are helping scientists to identify molecular mechanisms and genetic variants involved in normal sleep and sleep disorders.  Additional research will provide a better understanding of inherited sleep patterns and risks of circadian and sleep disorders. 

Sleep studies

Your healthcare provider may recommend a polysomnogram (sleep study) or other test to diagnose a sleep disorder.  A polysomnogram typically involves spending the night at a sleep lab or sleep center.  It records your breathing, oxygen levels, eye and limb movements, heart rate, and brain waves throughout the night.  Your sleep is also captured on video.  The data can help a sleep specialist determine if you are reaching and proceeding properly through the various sleep stages.  Results may be used to develop a treatment plan or determine if further tests are needed.

Tips for Getting a Good Night's Sleep

Getting enough sleep is important for your health.  Here are a few tips to improve your sleep:

• Set a schedule—go to bed and wake up at the same time each day.
• Exercise for at least 30 minutes most days of the week, but not within a few hours of bedtime.
• Avoid caffeine and nicotine late in the day and alcoholic drinks before bed.
• Relax before bed—try a warm bath, reading, or another relaxing routine.
• Create a room for sleep—avoid bright lights and loud sounds, keep the room at a comfortable temperature, and don’t watch TV or use a smartphone or computer  in your bedroom.
• Don’t lie in bed awake. If you can’t get to sleep, do something else, like reading or listening to calming music, until you feel tired. 
• See a doctor if you have problems sleeping or if you feel unusually tired during the day. Most sleep disorders can be treated effectively.

Hope Through Research

Scientists continue to learn about the function and regulation of sleep. A key focus of research is to understand the risks involved with being chronically sleep deprived and the relationship between sleep and disease. People who are chronically sleep deprived are more likely to be overweight, have strokes and cardiovascular disease, infections, and certain types of cancer than those who get enough sleep. Sleep disturbances are common among people with age-related neurological disorders such as Alzheimer’s disease and Parkinson’s disease. Many mysteries remain about the association between sleep and these health problems. Does the lack of sleep lead to certain disorders, or do certain diseases cause a lack of sleep? These, and many other questions about sleep, represent the frontier of sleep research.

Why Do We Need Sleep?

Contributing Writer

Lucy Bryan is a writer and editor with more than a decade of experience in higher education. She holds a B. A. in journalism from the University of North Carolina at Chapel Hill and an M.F.A. in creative writing from Penn State University.

Want to read more about all our experts in the field?

Dr. Brandon Peters

Sleep Physician, Sleep Psychiatry Expert

Brandon R. Peters, M.D., FAASM, is a double board-certified neurologist and sleep medicine specialist and fellow of the American Academy of Sleep Medicine who currently practices at Virginia Mason Franciscan Health in Seattle. He is a leading voice in sleep medicine who works at the cutting edge of medicine and technology to advance the field.

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Table of Contents

Why Getting Enough Sleep Is Important

The science behind why we sleep, how much sleep do i need, the effects of a lack of sleep, how to always get a good night’s sleep.

If you’ve stayed awake all night—by choice, out of necessity, or in spite of your efforts to sleep—you know just how critical sleep is to your wellbeing. Everyone needs sleep, but about one in three American adults don’t get enough of it.

The consequences of sleep deprivation are serious, so it’s worth learning why sleep matters, how it works, and how to give yourself the best chances of getting a good night’s sleep.

Sleep is an essential function that allows your body and mind to recharge, leaving you refreshed and alert when you wake up. Healthy sleep also helps the body remain healthy and stave off diseases. Without enough sleep, the brain cannot function properly, impairing your abilities to concentrate, think clearly, and process memories.

Is Your Troubled Sleep a Health Risk?

A variety of issues can cause problems sleeping. Answer three questions to understand if it’s a concern you should worry about.

Sleep serves a variety of important physical and psychological functions, including:  

• Learning and memory consolidation: Sleep helps with focus and concentration—and it allows the brain to register and organize memories —all of which are vital to learning.
• Emotional regulation: Sleep helps people regulate their emotions Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source and better manage the physical and psychological effects of stress.
• Judgment and decision making: Sleep influences a person’s ability to recognize danger and threats. Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source Healthy sleep supports sound judgment, good decision making, and other executive functions.
• Problem solving: Research shows that “sleeping on” a complex problem improves a person’s chance of solving it. Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source
• Energy conservation: Sleep allows people to conserve energy through an extended period of reduced activity.
• Growth and healing: Sleep provides the release of growth hormone necessary for the body’s tissues to grow and repair damage.
• Immunity: Sleep supports immune function , allowing the body to fight off diseases and infections.

Human beings, like all species on Earth, evolved to survive and thrive on a planet with a 24-hour cycle of day and night. According to some theories of sleep, Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source sleeping in one consolidated block at night allowed early humans to simultaneously avoid predators, conserve energy, and meet their need for rest. It also kept them from having to adapt to life in two very different conditions—daylight and darkness.

The biological patterns that help humans live according to the 24-hour day-night cycle are called circadian rhythms . These rhythms work alongside the sleep drive —a desire to sleep that grows in intensity the longer a person has been awake—to cause people to feel sleepy at night and alert in the morning. 

Circadian rhythms, including the sleep-wake cycle, operate according to environmental cues. Every evening, as darkness sets in, the body begins releasing the sleep hormone melatonin—and every morning, with the arrival of light , the body’s melatonin levels become undetectable. An evening drop and morning rise in body temperature accompanies this cycle, enhancing sleepiness and alertness at the right times.

Stages of Sleep

Our sleep architecture—that is, the way the body cycles through specific stages of sleep —enables the beneficial processes that occur during sleep, such as healing and learning. There are three non-rapid eye movement (non-REM) stages of sleep followed by rapid eye movement (REM), the final stage of sleep. Experiencing all four usually takes anywhere from 1.5 to 2 hours. Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source

• Stage N1: This is the lightest stage of sleep, and it usually only lasts a few minutes.
• Stage N2: Healthy adults usually spend about half of the night in N2 sleep. While brain activity slows, there are bursts of activity that may help with memory retention and learning.
• Stage N3: N3 sleep, also called “slow wave sleep” or “deep sleep,” helps a person wake up feeling refreshed. During this stage, blood pressure lowers, heart rate and breathing rate slow, and the body secretes growth hormone. People generally spend about 10% to 20% of the night in this stage. 
• REM Sleep: As its name suggests, people’s eyes intermittently move rapidly during this sleep stage. Most vivid dreaming takes place during REM sleep, and skeletal muscles become temporarily paralyzed to prevent a person from acting out their dreams. Memory consolidation occurs in this stage. It accounts for 20% to 25% of a typical night of sleep, with more of it occurring towards morning.

Healthy individuals cycle through all four stages of sleep multiple times a night. Regular sleep disruptions, as well as sleep disorders that affect sleep architecture like sleep apnea, can have serious consequences for physical health and mental health .

Experts generally recommend that adults get at least seven hours of sleep per night. Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source However, sleep needs can vary dramatically from person to person. Your activity level, your health status, and many other factors influence how much sleep you need , but the optimal number of hours typically falls within a specific range depending on your age and stage in life.

Not getting the amount of sleep your body needs can have serious consequences. Just one sleepless night can make it harder for you to focus and think clearly, and you might feel tired or sluggish during the day. You’re more likely to feel irritable and to exercise poor judgment when you haven’t had enough sleep. And sleep deprivation significantly elevates your risk Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source of making a mistake at work or having a car accident.

Long-term sleep deprivation carries all these risks and more. Chronic insufficient sleep may:

• Suppress your immune system, increasing your susceptibility to sickness and infection 
• Increase your risk of developing heart problems, type 2 diabetes, and high blood pressure 
• Interfere with your metabolism and elevate your risk for obesity 
• Cause your relationships to suffer at work and at home 
• Lead to depression and anxiety 

The effects of sleep debt compound quickly, so the sooner you can address sleep difficulties, the better.

The good news is that many sleep problems improve and even disappear when you take the right steps to treat them. Start by implementing healthy sleep hygiene practices at home.

• Get at least 20 minutes of exposure to natural light in the morning. 
• Commit to a regular sleep schedule.
• Adopt a relaxing bedtime routine.
• Make sure your bedroom environment is cool, dark, quiet, and comfortable.
• Avoid electronics with screens in the hour before bed.
• Exercise regularly and early in the day. 
• Avoid alcohol, nicotine, and caffeine in the hours before bed. 

If you have trouble sleeping even after taking these steps, contact your doctor. With the right treatments, you can get the sleep your body needs.

• New Research Evaluates Accuracy of Sleep Trackers
• Listening to Calming Words While Asleep Boosts Deep Sleep
• Distinct Sleep Patterns Linked to Health Outcomes
• Association Between Sleep Duration and Disturbance with Age Acceleration

About Our Editorial Team

Lucy Bryan, Contributing Writer

Medically Reviewed by

Dr. Brandon Peters, Sleep Physician, Sleep Psychiatry Expert

References 7 sources.

Vandekerckhove, M., & Wang, Y. L. (2017). Emotion, emotion regulation and sleep: An intimate relationship. AIMS neuroscience, 5(1), 1–17.

Khan, M. A., & Al-Jahdali, H. (2023). The consequences of sleep deprivation on cognitive performance. Neurosciences (Riyadh, Saudi Arabia), 28(2), 91–99.

Sio, U. N., Monaghan, P., & Ormerod, T. (2013). Sleep on it, but only if it is difficult: effects of sleep on problem solving. Memory & cognition, 41(2), 159–166.

Freiberg A. S. (2020). Why We Sleep: A Hypothesis for an Ultimate or Evolutionary Origin for Sleep and Other Physiological Rhythms. Journal of circadian rhythms, 18, 2.

Kirsch, D. (2024, March). Stages and architecture of normal sleep. In S. Harding & A.Eichler (Ed.). UpToDate.

Consensus Conference Panel, Watson, N. F., Badr, M. S., Belenky, G., Bliwise, D. L., Buxton, O. M., Buysse, D., Dinges, D. F., Gangwisch, J., Grandner, M. A., Kushida, C., Malhotra, R. K., Martin, J. L., Patel, S. R., Quan, S. F., Tasali, E., Non-Participating Observers, Twery, M., Croft, J. B., Maher, E., … Heald, J. L. (2015). Recommended amount of sleep for a healthy adult: A joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine, 11(6), 591–592.

Maski, K. (2024, March). Insufficient sleep: Evaluation and management. In T. Scammell & A. Eichler (Ed.). UpToDate.

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How Age Affects Your Circadian Rhythm

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Chronotypes: Definition, Types, & Effect on Sleep

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Daylight Saving Time: Everything You Need to Know

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Does Napping Impact Your Sleep at Night?

Does Daytime Tiredness Mean You Need More Sleep?

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Sleep Debt: The Hidden Cost of Insufficient Rest

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How Sleep Works: Understanding the Science of Sleep

What Makes a Good Night's Sleep

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Sleep and Social Media

Adenosine and Sleep: Understanding Your Sleep Drive

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Microsleep: What Is It, What Causes It, and Is It Safe?

Light Sleeper: What It Means and What To Do About It

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Good Sleep for Good Health

Get the Rest You Need

Sometimes, the pace of modern life barely gives you time to stop and rest. It can make getting a good night’s sleep on a regular basis seem like a dream.

But sleep is as important for good health as diet and exercise. Good sleep improves your brain performance, mood, and health.

Not getting enough quality sleep regularly raises the risk of many diseases and disorders. These range from heart disease and stroke to obesity and dementia.

There’s more to good sleep than just the hours spent in bed, says Dr. Marishka Brown, a sleep expert at NIH. “Healthy sleep encompasses three major things,” she explains. “One is how much sleep you get. Another is sleep quality—that you get uninterrupted and refreshing sleep. The last is a consistent sleep schedule.”

People who work the night shift or irregular schedules may find getting quality sleep extra challenging. And times of great stress—like the current pandemic—can disrupt our normal sleep routines. But there are many things you can do to improve your sleep.

Sleep for Repair

Why do we need to sleep? People often think that sleep is just “down time,” when a tired brain gets to rest, says Dr. Maiken Nedergaard, who studies sleep at the University of Rochester.

“But that’s wrong,” she says. While you sleep, your brain is working. For example, sleep helps prepare your brain to learn, remember, and create.

Nedergaard and her colleagues discovered that the brain has a drainage system that removes toxins during sleep.

“When we sleep, the brain totally changes function,” she explains. “It becomes almost like a kidney, removing waste from the system.”

Her team found in mice that the drainage system removes some of the proteins linked with Alzheimer’s disease. These toxins were removed twice as fast from the brain during sleep.

Everything from blood vessels to the The system that protects your body from invading viruses, bacteria, and other microscopic threats. immune system uses sleep as a time for repair, says Dr. Kenneth Wright, Jr., a sleep researcher at the University of Colorado.

“There are certain repair processes that occur in the body mostly, or most effectively, during sleep,” he explains. “If you don’t get enough sleep, those processes are going to be disturbed.”

Sleep Myths and Truths

How much sleep you need changes with age. Experts recommend school-age children get at least nine hours a night and teens get between eight and 10. Most adults need at least seven hours or more of sleep each night.

There are many misunderstandings about sleep. One is that adults need less sleep as they get older. This isn’t true. Older adults still need the same amount. But sleep quality can get worse as you age. Older adults are also more likely to take medications that interfere with sleep.

Another sleep myth is that you can “catch up” on your days off. Researchers are finding that this largely isn’t the case.

“If you have one bad night’s sleep and take a nap, or sleep longer the next night, that can benefit you,” says Wright. “But if you have a week’s worth of getting too little sleep, the weekend isn’t sufficient for you to catch up. That’s not a healthy behavior.”

In a recent study, Wright and his team looked at people with consistently deficient sleep. They compared them to sleep-deprived people who got to sleep in on the weekend.

Both groups of people gained weight with lack of sleep. Their bodies’ ability to control blood sugar levels also got worse. The weekend catch-up sleep didn’t help.

On the flip side, more sleep isn’t always better, says Brown. For adults, “if you’re sleeping more than nine hours a night and you still don’t feel refreshed, there may be some underlying medical issue,” she explains.

Sleep Disorders

Some people have conditions that prevent them from getting enough quality sleep, no matter how hard they try. These problems are called sleep disorders.

The most common sleep disorder is insomnia. “Insomnia is when you have repeated difficulty getting to sleep and/or staying asleep,” says Brown. This happens despite having the time to sleep and a proper sleep environment. It can make you feel tired or unrested during the day.

Insomnia can be short-term, where people struggle to sleep for a few weeks or months. “Quite a few more people have been experiencing this during the pandemic,” Brown says. Long-term insomnia lasts for three months or longer.

Sleep apnea is another common sleep disorder. In sleep apnea, the upper airway becomes blocked during sleep. This reduces or stops airflow, which wakes people up during the night. The condition can be dangerous. If untreated, it may lead to other health problems.

If you regularly have problems sleeping, talk with your health care provider. They may have you keep a sleep diary to track your sleep for several weeks. They can also run tests, including sleep studies. These look for sleep disorders.

Getting Better Sleep

If you’re having trouble sleeping, hearing how important it is may be frustrating. But simple things can improve your odds of a good night’s sleep. See the Wise Choices box for tips to sleep better every day.

Treatments are available for many common sleep disorders. Cognitive behavioral therapy can help many people with insomnia get better sleep. Medications can also help some people.

Many people with sleep apnea benefit from using a device called a CPAP machine. These machines keep the airway open so that you can breathe. Other treatments can include special mouthguards and lifestyle changes.

For everyone, “as best you can, try to make sleep a priority,” Brown says. “Sleep is not a throwaway thing—it’s a biological necessity.”

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The Future of Sleep Studies

Most people have a general idea of what happens during a sleep study . You spend the night sleeping in a laboratory “all wired up” while doctors run tests. 

However, the future of sleep research looks much different, according  Charlene Gamaldo, M.D.  , medical director of  Johns Hopkins Center for Sleep  at Howard County General Hospital.  “Sleep clinical care and research is in a revolutionary place because of technology,” says Gamaldo. “The brick-and-mortar model of conducting sleep studies in a medical care center is really going to be fading into the sunset or will be minimal at best.”

New approaches to testing are likely to take place in the comfort of your own home.

At-Home Sleep Testing Devices

Conducting sleep tests at home is going to become a lot more common, says Gamaldo. “Many of the portable devices currently available show a lot of promise with producing information that is in line with what we see in the lab,” she says. “These technologies can monitor people’s sleep or what’s going on with their breathing during sleep,” she says. Johns Hopkins uses several FDA-approved at-home devices for:

• Measuring sleep brain wave activity,  which can show doctors how quickly you fall asleep, how deeply you sleep and whether rest quality is good
• Assessing leg movements  to detect restless legs syndrome
• Monitoring breathing  to help diagnose sleep apnea. In addition, home monitoring captures how well you rest in the comfort of your own home. Sleeping in a lab does not give doctors or researchers an idea of what a typical night’s sleep is like for you in your bedroom or sleep environment.

While these portable devices are becoming increasingly more accurate, some people may still need to come to the lab for a more comprehensive or sophisticated look at their biorhythms during sleep, says Gamaldo.

A lab has the advantage of being a controlled environment where you’re under constant observation by a researcher in the case of more technically involved sleep monitoring. “If a wire falls off while you’re sleeping, there’s someone there to put it back on,” she says.

Wearable Technology and Phone Apps

Smartphone apps and wearable tracking devices will become more common in the sleep research field,” says Gamaldo. “There are apps now that record a person snoring at home. We hope to eventually correlate the information with actual features of sleep disorders, which could indicate the presence of conditions like sleep apnea. Not too long ago, this was a disorder we could only diagnose in the sleep lab.”  Scientists need to compare the information that the tracking devices and apps gather to the data that researchers and doctors gather in a lab setting, she says. These devices are convenient and can significantly increase access to care. However, researchers need to make sure that apps and trackers undergo rigorous and reportable validation studies. The public needs to be sure that that these devices actually do what they claim, she adds.

Researchers and doctors are increasingly able to use telehealth, or communication technologies, to provide care for their patients. For example, video web conferences can help doctors and researchers consult with patients about sleep health. Clinicians and scientists can also share data and information with each other for research purposes.  Providing care through telehealth allows doctors to reach people who live in rural areas, away from large medical centers. Doctors can also use this technology to serve those living in countries with fewer health resources, says Gamaldo.

What Researchers Will Be Studying

While sleep disorders have always existed, they have been underdiagnosed, says Gamaldo. Researchers want to explore better ways to diagnose and treat conditions such as sleep apnea, restless legs syndrome and insomnia.  Scientists will also continue to study the effects of not getting enough sleep. Chronic sleep loss is now recognized as an epidemic in the United States growing in prevalence and severity. “Each year Americans are shaving more and more time off of the sleep they get per night,” says Gamaldo.  “More individuals are doing shift work, and people are distracted in the evening hours by cable TV with 1,000s of channels, computer streaming, binge watching, not to mention our growing dependence on mobile phones and social media.” Each generation of these devices brings a better and brighter screen that causes greater exposure to blue light that can interfere with your body clock, creating problems with sleep.  Researchers also want to study how lack of sleep and poor quality sleep impacts other conditions such as diabetes and heart disease, she says.

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Sleep Deprivation and Deficiency How Sleep Affects Your Health

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Getting enough quality sleep at the right times can help protect your mental health, physical health, quality of life, and safety.

How do I know if I’m not getting enough sleep?

Sleep deficiency can cause you to feel very tired during the day. You may not feel refreshed and alert when you wake up. Sleep deficiency also can interfere with work, school, driving, and social functioning.

How sleepy you feel during the day can help you figure out whether you're having symptoms of problem sleepiness.

You might be sleep deficient if you often feel like you could doze off while:

• Sitting and reading or watching TV
• Sitting still in a public place, such as a movie theater, meeting, or classroom
• Riding in a car for an hour without stopping
• Sitting and talking to someone
• Sitting quietly after lunch
• Sitting in traffic for a few minutes

Sleep deficiency can cause problems with learning, focusing, and reacting. You may have trouble making decisions, solving problems, remembering things, managing your emotions and behavior, and coping with change. You may take longer to finish tasks, have a slower reaction time, and make more mistakes.

Symptoms in children

The symptoms of sleep deficiency may differ between children and adults. Children who are sleep deficient might be overly active and have problems paying attention. They also might misbehave, and their school performance can suffer.

Sleep-deficient children may feel angry and impulsive, have mood swings, feel sad or depressed, or lack motivation.

Sleep and your health

The way you feel while you're awake depends in part on what happens while you're sleeping. During sleep, your body is working to support healthy brain function and support your physical health. In children and teens, sleep also helps support growth and development.

The damage from sleep deficiency can happen in an instant (such as a car crash), or it can harm you over time. For example, ongoing sleep deficiency can raise your risk of some chronic health problems. It also can affect how well you think, react, work, learn, and get along with others.

Mental health benefits

Sleep helps your brain work properly. While you're sleeping, your brain is getting ready for the next day. It's forming new pathways to help you learn and remember information.

Studies show that a good night's sleep improves learning and problem-solving skills. Sleep also helps you pay attention, make decisions, and be creative.

Studies also show that sleep deficiency changes activity in some parts of the brain. If you're sleep deficient, you may have trouble making decisions, solving problems, controlling your emotions and behavior, and coping with change. Sleep deficiency has also been linked to depression, suicide, and risk-taking behavior.

Children and teens who are sleep deficient may have problems getting along with others. They may feel angry and impulsive, have mood swings, feel sad or depressed, or lack motivation. They also may have problems paying attention, and they may get lower grades and feel stressed.

Physical health benefits

Sleep plays an important role in your physical health.

Good-quality sleep:

• Heals and repairs your heart and blood vessels.
• Helps support a healthy balance of the hormones that make you feel hungry (ghrelin) or full (leptin): When you don't get enough sleep, your level of ghrelin goes up and your level of leptin goes down. This makes you feel hungrier than when you're well-rested.
• Affects how your body reacts to insulin: Insulin is the hormone that controls your blood glucose (sugar) level. Sleep deficiency results in a higher-than-normal blood sugar level, which may raise your risk of diabetes.
• Supports healthy growth and development: Deep sleep triggers the body to release the hormone that promotes normal growth in children and teens. This hormone also boosts muscle mass and helps repair cells and tissues in children, teens, and adults. Sleep also plays a role in puberty and fertility.
• Affects your body’s ability to fight germs and sickness: Ongoing sleep deficiency can change the way your body’s natural defense against germs and sickness responds. For example, if you're sleep deficient, you may have trouble fighting common infections.
• Decreases   your risk of health problems, including heart disease, high blood pressure, obesity, and stroke.

Research for Your Health

NHLBI-funded research found that adults who regularly get 7-8 hours of sleep a night have a lower risk of obesity and high blood pressure. Other NHLBI-funded research found that untreated sleep disorders rase the risk for heart problems and problems during pregnancy, including high blood pressure and diabetes.

Daytime performance and safety

Getting enough quality sleep at the right times helps you function well throughout the day. People who are sleep deficient are less productive at work and school. They take longer to finish tasks, have a slower reaction time, and make more mistakes.

After several nights of losing sleep — even a loss of just 1 to 2 hours per night — your ability to function suffers as if you haven't slept at all for a day or two.

Lack of sleep also may lead to microsleep. Microsleep refers to brief moments of sleep that happen when you're normally awake.

You can't control microsleep, and you might not be aware of it. For example, have you ever driven somewhere and then not remembered part of the trip? If so, you may have experienced microsleep.

Even if you're not driving, microsleep can affect how you function. If you're listening to a lecture, for example, you might miss some of the information or feel like you don't understand the point. You may have slept through part of the lecture and not realized it.

Some people aren't aware of the risks of sleep deficiency. In fact, they may not even realize that they're sleep deficient. Even with limited or poor-quality sleep, they may still think they can function well.

For example, sleepy drivers may feel able to drive. Yet studies show that sleep deficiency harms your driving ability as much or more than being drunk. It's estimated that driver sleepiness is a factor in about 100,000 car accidents each year, resulting in about 1,500 deaths.

Drivers aren't the only ones affected by sleep deficiency. It can affect people in all lines of work, including healthcare workers, pilots, students, lawyers, mechanics, and assembly line workers.

Lung Health Basics: Sleep

People with lung disease often have  trouble sleeping. Sleep is critical to overall health, so take the first step to sleeping better: learn these sleep terms, and find out about treatments that can help with sleep apnea.

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Article Contents

Extending weeknight sleep duration in late-sleeping adolescents using morning bright light on weekends: a 3-week maintenance study.

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Stephanie J Crowley, Elaine Poole, John Adams, Charmane I Eastman, Extending weeknight sleep duration in late-sleeping adolescents using morning bright light on weekends: a 3-week maintenance study, SLEEP Advances , 2024;, zpae065, https://doi.org/10.1093/sleepadvances/zpae065

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Our sleep extension intervention in adolescents showed that gradually shifting weekday bedtime earlier plus one weekend of morning bright light advanced circadian phase and increased weeknight sleep duration. Here, we examine at-home maintenance of these changes.

Fourteen adolescents (15.3-17.9 years; 7 female) completed a 7-week study. After usual sleep at home (2-week baseline), intervention participants (n=8) gradually advanced weekday bedtime (1h earlier than baseline during week 3; 2h earlier in week 4) and received bright light (~6000lux; 2.5h) on both mornings of the intervening weekend. During 3 maintenance weeks, intervention participants were instructed to maintain their school-day wake-up time on all days, keep their early week 4 bedtimes, except on weekends when they could go to bed up to 1h later, and get a 2.5-h light box exposure within 5 min of waking on one morning (Saturday/Sunday) of both weekends at home. Control participants (n=6) slept as usual at home and did not receive weekend bright light. DLMO was measured after the 2-week baseline, 2-week intervention, and 3-week maintenance in all participants. Actigraphic sleep/wake was collected throughout.

After the 2-week intervention, DLMOs advanced more compared to control (37.0±40.0 mins vs. -14.7±16.6 mins), weekday sleep duration increased by 69.7±27.8 min and sleep onset was 103.7±14.2 mins earlier compared to baseline. After 3 maintenance weeks, intervention participants showed negligible DLMO delays (-4.9±22.9 mins); weekday fall asleep times and sleep durations also remained stable.

Early circadian phase and extended sleep can be maintained with at-home weekend bright light.

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Screen Use at Bedtime and Sleep Duration and Quality Among Youths

• 1 Department of Medicine, University of Otago, Dunedin, New Zealand
• 2 Biostatistics Centre, University of Otago, Dunedin, New Zealand
• 3 Department of Women’s and Children’s Health, University of Otago, Dunedin, New Zealand

Question   Is there an association between screen time before bed and sleep duration and quality in youths?

Findings   In this repeated-measures cohort study of 79 participants aged 11 to 14 years, objectively measured screen time in the 2 hours before bed had no association with most measures of sleep health. Screen time once in bed, particularly interactive screen activities, such as gaming and multitasking, was associated with less sleep.

Meaning   The findings showed that not all screen time before bed was associated with impaired sleep, suggesting that presleep recommendations require modification.

Importance   Although questionnaire-based cross-sectional research suggests that screen time before bed correlates with poor sleep, self-reported data seem unlikely to capture the complexity of modern screen use, requiring objective night-by-night measures to advance this field.

Objective   To examine whether evening screen time is associated with sleep duration and quality that night in youths.

Design, Setting, and Participants   This repeated-measures cohort study was performed from March to December 2021 in participant homes in Dunedin, New Zealand. Participants included healthy youths aged 11 to 14.9 years. Data were analyzed from October to November 2023.

Exposure   Objectively measured screen time, captured using wearable or stationary video cameras from 2 hours before bedtime until the first time the youth attempted sleep (shut-eye time) over 4 nonconsecutive nights. Video data were coded using a reliable protocol (κ = 0.92) to quantify device (8 options [eg, smartphone]) and activity (10 options [eg, social media]) type.

Main Outcomes and Measures   Sleep duration and quality were measured objectively via wrist-worn accelerometers. The association of screen use with sleep measures was analyzed on a night-by-night basis using mixed-effects regression models including participant as a random effect and adjusted for weekends.

Results   Of the 79 participants (47 [59.5%] male; mean [SD] age, 12.9 [1.1] years), all but 1 had screen time before bed. Screen use in the 2 hours before bed had no association with most measures of sleep health that night (eg, mean difference in total sleep time, 0 minutes [95% CI, –3 to 20 minutes] for every 10 minutes more total screen time). All types of screen time were associated with delayed sleep onset but particularly interactive screen use (mean difference, 10 minutes; 95% CI, 4 to 16 minutes for every additional 10 minutes of interactive screen time). Every 10 minutes of additional screen time in bed was associated with shorter total sleep time (mean difference, –3 minutes; 95% CI, –6 to –1 minute). The mean difference in total sleep time was −9 minutes (95% CI, −16 to −2 minutes) for every 10 minutes of interactive screen use and −4 minutes (95% CI, −7 to 0 minutes) for passive screen use. In particular, gaming (mean difference, –17 minutes; 95% CI, –28 to –7 minutes for every 10 minutes of gaming) and multitasking (mean difference, −35 minutes; 95% CI, –67 to –4 minutes on nights with vs without multitasking) were associated with less total sleep time.

Conclusions and Relevance   In this repeated-measures cohort study, use of an objective method showed that screen time once in bed was associated with impairment of sleep, especially when screen time was interactive or involved multitasking. These findings suggest that current sleep hygiene recommendations to restrict all screen time before bed seem neither achievable nor appropriate.

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Brosnan B , Haszard JJ , Meredith-Jones KA , Wickham S , Galland BC , Taylor RW. Screen Use at Bedtime and Sleep Duration and Quality Among Youths. JAMA Pediatr. Published online September 03, 2024. doi:10.1001/jamapediatrics.2024.2914

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Study shows potential 20% reduction in heart disease based on weekend sleep

by Liz Bonis, WKRC

CINCINNATI (WKRC) - A new study is showing that there may be a link between your weekend sleep and your heart.

The study showed that the perfect prescription for good health may be sleeping in on the weekends.

It was recently presented at the European Society of Cardiology's annual congress. The researchers found that catching up on sleep over the weekend could reduce your risk of developing heart disease by nearly 20% and that it may be even more beneficial if you have a hard time getting enough sleep during the week.

Local 12 asked sleep specialists at Ohio's Christ Hospital why this may be true, especially when it contradicts previous research that always said you should keep a similar sleep schedule all throughout the week.

"My take on this study is, first of all, focus on preventing the sleep deprivation if you can. Aim for seven-hour nights every night. If you feel like you're deprived, then use a little bit of moderate sleep on the weekend. Sleeping in is okay," said sleep medicine specialist Dr. Karthikeyan Kanagarajan.

As part of the study, researchers followed the health outcomes of more than half a million people. All of those people were between the ages of 40 and 69.

When the researchers compared those who got more sleep on the weekends to those who got less, after 14 years, the group that got more weekend sleep not only had a lower risk of developing heart disease, but they were also less likely to develop heart failure, atrial fibrillation, and stroke.

"Consistent bedtime; no gadgets close to bedtime; no TV; that's the hardest part. Keep the gadgets away; avoid caffeine, nicotine, and stimulants so you can avoid those things that can affect your sleep," said Dr. Kanagarajan.

While it's still not clear from this study as to why this weekend sleep prescription works, researchers said that a lack of sleep is now linked with everything from high blood pressure to weight gain, all of which can influence the heart.

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It’s Almost Impossible to Keep Teens off Their Phones in Bed – But New Research Shows It Really Does Affect Their Sleep

Sep 4, 2024 | Quality | 0 |

By Rachael Taylor , University of Otago

Parents of children and teenagers have long been warned about the dangers of screen time and digital devices before bed – the worry being that screens could harm the sleep patterns of young people.

But do screens really hurt the length and quality of sleep?

Our new research found that using screens in bed was worse for sleep than using screens for hours before going to bed.

Sleep guidelines recommend no screen use in the hour or two before bed. But we found screen time in the two hours before bed had little impact on young people’s sleep. Instead, it was screen time once in bed that caused problems.

Using cameras to track device usage and sleep, we found using a device in bed could cause more harm than screen time right up to bedtime.

These findings challenge long-held assumptions about screen time at night and could help parents improve the quality of their children’s sleep.

Connecting Sleep and Screens

A number of global organisations recommend adolescents stop using devices in the hour or two before bed, and instead undertake activities like reading a book or quiet time with the family.

But these recommendations are based on research with a number of limitations. The studies were designed in such a way that researchers could link sleep and screens. But they don’t tell us if changes in how young people used screens had an affect on the length or quality of sleep.

Most of the existing research also used questionnaires to assess both screen time and sleep. Questionnaires are unlikely to capture true screen time accurately, particularly if you are interested in knowing more than just how long an adolescent has spent on their device.

To address some of these weaknesses in the previous research, we asked 85 adolescents aged between 11 and 14 to wear a body camera on their chest for the three hours before bed, for four nights.

These cameras faced outwards and accurately captured when, what and how adolescents used their screens. Because we were interested in overnight screen time as well, a second infrared camera was placed on a tripod in the teenagers bedroom and captured their screen time while in bed. The research participants also wore an actigraph – a watch-sized device that objectively measured screen time.

Teen Nighttime Activity

It quickly became obvious the adolescents spent a lot of their screen time while in bed.

Our analysis looked at two time periods – from the two hours before they got into bed, and from once they were in bed (clearly under the covers) until they put their devices down and were clearly trying to go to sleep.

Our data showed 99% of the adolescents used screens in the two hours before bed, more than half once they were in bed, and a third even after first trying to go to sleep for the night. Just one teenager did not use screens before bed on any of the four nights.

The screen time before they got into bed had little impact on their sleep that night. However, screen time once in bed did impair their sleep. It stopped them from going to sleep for about half an hour, and reduced the amount of sleep they got that night.

This was particularly true for more interactive screen activities like gaming and multitasking – when they use more than one device at the same time (like watching a movie on Netflix on a laptop while playing Xbox on a gaming device).

In fact, every additional ten minutes of this type of screen time reduced the amount of sleep they got that night by almost the same amount – nine minutes.

Revisiting Guidelines

Our research was an observational study looking at the established screen habits of young people.

The next step to better understanding this will be to conduct experiments that can actually prove different types and timings of screen time affect sleep.

That said, what we have already found challenges existing guidelines. Screens at night may not be the bogey man they have been made out to be. But allowing young people to have screens in bed can be detrimental to their quality of sleep.

Rachael Taylor , Professor, Department of Medicine, University of Otago

This article is republished from The Conversation under a Creative Commons license. Read the original article .

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Sleeping hours: what is the ideal number and how does age impact this?

Jean-philippe chaput.

1 Healthy Active Living and Obesity Research Group, Children’s Hospital of Eastern Ontario Research Institute, Ottawa, ON, Canada, ac.no.oehc@tupahcpj

2 Department of Pediatrics, University of Ottawa, Ottawa, ON, Canada, ac.no.oehc@tupahcpj

3 School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada, ac.no.oehc@tupahcpj

4 School of Epidemiology and Public Health, University of Ottawa, Ottawa, ON, Canada, ac.no.oehc@tupahcpj

Caroline Dutil

Hugues sampasa-kanyinga.

The objective of this narrative review paper is to discuss about sleep duration needed across the lifespan. Sleep duration varies widely across the lifespan and shows an inverse relationship with age. Sleep duration recommendations issued by public health authorities are important for surveillance and help to inform the population of interventions, policies, and healthy sleep behaviors. However, the ideal amount of sleep required each night can vary between different individuals due to genetic factors and other reasons, and it is important to adapt our recommendations on a case-by-case basis. Sleep duration recommendations (public health approach) are well suited to provide guidance at the population-level standpoint, while advice at the individual level (eg, in clinic) should be individualized to the reality of each person. A generally valid assumption is that individuals obtain the right amount of sleep if they wake up feeling well rested and perform well during the day. Beyond sleep quantity, other important sleep characteristics should be considered such as sleep quality and sleep timing (bedtime and wake-up time). In conclusion, the important inter-individual variability in sleep needs across the life cycle implies that there is no “magic number” for the ideal duration of sleep. However, it is important to continue to promote sleep health for all. Sleep is not a waste of time and should receive the same level of attention as nutrition and exercise in the package for good health.

Introduction

Sleep is increasingly recognized as a critical component of healthy development and overall health. 1 – 3 Healthy sleep comprises many dimensions, including adequate duration, good quality, appropriate timing, and the absence of sleep disorders. 4 , 5 Not getting enough sleep at night is generally associated with daytime sleepiness, daytime fatigue, depressed mood, poor daytime functioning, and other health and safety problems. 6 – 9 Chronic insufficient sleep has become a concern in many countries, given its association with morbidity and mortality. 10 , 11 For example, habitual short sleep duration has been associated with adverse health outcomes including obesity, 12 type 2 diabetes, 13 hypertension, 14 cardiovascular disease, 15 depression, 16 and all-cause mortality. 17 Interest in finding ways to improve sleep patterns of individuals at the population-level standpoint is growing, and experts recommend that sleep should be considered more seriously by public health bodies, ie, given as much attention and resources as nutrition and physical activity. 18 – 20

Guidelines on the recommended amount of sleep needed for optimal health exist; they are a vital tool for surveillance, they help inform policies, they can provide a starting point for intervention strategies, and they educate the general public about healthy sleep behaviors. However, sleep needs may vary from one person to another at any given age across the lifespan. Additionally, some age groups and populations are more likely to report insufficient sleep duration and may be at greater risk for detrimental health outcomes. 5 , 6 , 11 The objective of this narrative review article is to discuss whether or not an ideal amount of sleep exists for optimal health and how it is impacted by age.

Insufficient sleep across the lifespan

Insufficient sleep has become widespread over the last decades, especially among adolescents. 11 , 21 Both physiological factors and exogenous exposures come into play in explaining insufficient sleep in this age group. Sleep curtailment is often attributed to extrinsic factors, such as artificial light, caffeine use, lack of physical activity, no bedtime rules in the household, and the increased availability of information and communication technologies. 22 – 25 In adolescence, insufficient sleep has also been attributed to intrinsic factors such as pubertal hormonal changes, which is associated with a shift toward an evening chronotype 26 that may also lead to an asynchrony between the biological clock, characterized by a phase delay, and the social clock. 27 In adolescents, this biological phase delay combined with the social clock, for which the main synchronizer is the fixed and early school start time, contributes to the observed sleep deficits in this population. 27 The conflict between intrinsic and extrinsic factors, biological time and social time, has been indicated to be greater during adolescence than at any other point in our lives. 28

Despite some overlap between factors that could explain insufficient sleep among adolescents and adults, such as exposure to artificial light at night, lack of physical activity, caffeine consumption, and poor sleep hygiene, other factors that could specifically be related to insufficient sleep among adults may include but not be limited to work demands, social commitments, health and/or affective problems, and family dynamics (eg, working mothers and children with full agendas). 10

In the elderly, sleep patterns and distribution undergoes significant quantitative and qualitative changes. Older adults tend to have a harder time falling asleep and more trouble staying asleep. This period of life is often accompanied by a circadian shift to a morning chronotype, as opposed to the evening chronotype change during adolescence, that results in early bedtime and risetime. 29 Research suggests that the need for sleep may not change with age, but it is the ability to get the needed sleep that decreases with age. 10 This decreased ability to sleep in older adults is often secondary to their comorbidities and related medications (polypharmacy) rather than normal aging processes per se. 30 – 32 Furthermore, the increased frequency of sleep-related disorders in the elderly population contribute to much of the sleep deficiencies observed in this population. 33 – 36 Inadequate sleep in the elderly could also be related to other factors, such as life changes (eg, retirement, physical inactivity, decreased social interactions), age-related changes in metabolism, and environmental changes (eg, placement in a nursing home). 37

A systematic review and meta-analysis reported that in the elderly population both short and long sleep are independently associated with increased risk of cardiovascular-related and cancer-related mortality. 38 Additionally, adjustments for health conditions in the studies examining the association between sleep duration and mortality risks did not attenuate the strength of the association between long sleep and increased risk of mortality, which suggests that the mechanisms in these associations may differ between long sleep and short sleep duration. 38 One possible explanation for this association, between long sleep duration and increased risk of non-communicable diseases related mortality, may be related to the increased prevalence of sleep fragmentation in this population. 38 , 39 While older adults may report long sleep duration, other sleep characteristics, namely sleep architecture and quality, are altered by sleep fragmentation. As the relationship between long sleep duration and increased risk of cardiovascular-related and cancer-related mortality is unique to the elderly population, the causality should be further investigated.

Normative sleep duration values across the lifespan

Sleep–wake regulation and sleep states evolve very rapidly during the first year of life. 40 For example, newborns (0–3 months) do not have an established circadian rhythm and therefore their sleep is distributed across the full 24-hour day. 41 At 10–12 weeks, the circadian rhythm emerges and sleep becomes more nocturnal between ages 4 and 12 months. 42 Children continue to take daytime naps between 1 and 4 years of age, and night wakings are common. 43 Daytime naps typically stop by the age of 5 years and overnight sleep duration gradually declines throughout childhood, in part due to a shift to later bedtimes and unchanged wake times. 43

Sleep patterns are explained by a complex interplay between genetic, behavioral, environmental, and social factors. Examples of factors that can determine sleep duration include daycare/school schedules, parenting practices, cultural preferences, family routines, and individual differences in genetic makeup. Despite inter-individual differences in sleep duration, international normative data exist to show the normal distribution of sleep duration for different age groups. However, it is important to keep in mind that normative reference values by no means indicate anything about what the ideal or optimal sleep duration should be, ie, the amount of sleep associated with health benefits. Nevertheless, they tell us about what is normal (or not) in the population and provide a valuable yardstick for practitioners and educators when dealing with sleep-related issues.

A meta-analysis by Galland et al 44 examined the scientific literature with regards to normal sleep patterns in infants and children aged 0–12 years. The review included 69,542 participants from 18 countries and subjective measures were used to determine sleep duration (sleep diary or questionnaire). They calculated mean reference values and ranges (±1.96 SD) for sleep duration of 12.7 h/day (9.0–13.3) for infants (<2 years), 11.9 h/day (9.9–13.8) for toddlers/preschoolers (ages 2–5 years), and 9.2 h/day (7.6–10.8) for children (6–12 years). Normative sleep duration data across age categories are shown in Figure 1 . A strong inverse relationship with age was evident from these data, with the fastest rate of decline observed over the first 6 months of life (10.5 min/month decline in sleep duration). The review also highlighted that Asians had significantly shorter sleep (1 hour less over the 0–12-year range) compared to Caucasians or other ethnic groups. Overall, these reference values should be considered as global norms because the authors combined different countries and cultures.

Normal self-reported sleep durations in children aged 0–12 years.

Note: The mean reference values are from a meta-analysis of 34 studies from 18 countries. 44

Abbreviations: m, months; y, years.

Galland et al 45 also reported in 2018 normative sleep duration values for children aged 3–18 years as measured with actigraphy (objective assessment of sleep duration). Their meta-analysis included 79 articles and involved children from 17 countries. As shown in Figure 2 , pooled mean estimates for overnight sleep duration declined from 9.68 hours (3–5 years age band) to 8.98 hours (6–8 years age band), 8.85 hours (9–11 years age band), 8.05 hours (12–14 years age band), and 7.4 hours (15–18 years age band). These normative sleep duration values may aid in the interpretation of actigraphy measures from nighttime recordings in the pediatric population for any given age.

Normal actigraphy-determined sleep duration values in children aged 3–18 years.

Note: The mean reference values are from a meta-analysis of 79 studies from 17 countries. 45

A meta-analysis of objectively assessed sleep from childhood to adulthood was also published by Ohayon et al 46 in 2004 to determine normative sleep values across the lifespan. A total of 65 studies representing 3,577 healthy individuals aged 5–102 years were included. Polysomnography or actigraphy was used to assess sleep duration in the included studies. They observed that total sleep time significantly decreased with age in adults, while it was the case in children and adolescents only in studies performed on school days. This pattern suggests that, in children and adolescents, the decrease in total sleep time is not related to maturation but to other factors such as earlier school start times.

In summary, normative sleep duration values are helpful in providing information on what constitutes the norm for a given age and what is considered outside the norm. These reference values are impacted by the method used to determine sleep duration (objective vs subjective assessment) and provide norms at the population-level standpoint. Many factors can determine sleep duration at the individual level. Although international normative data provide information about the normal distribution of sleep duration in the population, they do not identify the duration associated with health benefits. For example, having a sleep duration that fits with the average of the population is by no means indicative of either a good or a bad sleep amount. Optimal sleep duration, or the amount of sleep associated with favorable outcomes, is what is used for public health recommendations and is discussed in the next section.

Recommended amount of sleep across the lifespan

In 2015, the National Sleep Foundation in the US released their updated sleep duration recommendations to make scientifically sound and practical recommendations for daily sleep duration across the lifespan. 47 The same year, the American Academy of Sleep Medicine and the Sleep Research Society released a consensus recommendation for the amount of sleep needed to promote optimal health in adults. 48 The year after, they released their recommended amount of sleep for pediatric populations. 49 Both sleep guidelines issued by the US used a similar developmental approach to deliver their sleep duration recommendations, which included a consensus and a voting process with a multidisciplinary expert panel. The sleep duration recommendations can be found in Table 1 .

Sleep duration recommendations in the US and Canada

Note: Papers describing the sleep duration recommendations can be found elsewhere. 47 – 51

Abbreviations: AASM, American Academy of Sleep Medicine; SRS, Sleep Research Society.

Many organizations around the world have their own sleep duration recommendations, and the aim of this article is not to review the different sleep duration guidelines. Overall, they are all very similar, and often reference the recommendations from the US. In Canada, robust and evidence-informed sleep guidelines became available in 2016. 50 , 51 The sleep recommendations in Canada for children of all ages, also known as the 24-hour guidelines, are integrated with physical activity and sedentary behavior recommendations to cover the entire 24-hour period (sleep/wake period). This allows to put more emphasis on the overall “cocktail” of behaviors for a healthier 24-hour day, rather than isolating individual behaviors. This integrated approach to health, with a focus on the interrelationships among sleep, sedentary behavior, and physical activity, is an important advancement in public health messaging. It emphasizes that all of these behaviors matter equally, and balancing all three is required for favorable health outcomes.

The Canadian 24-hour guidelines were the impetus for the development of similar guidelines in Australia, 52 New Zealand, 53 and the initiation of similar global guidelines by the World Health Organization. Similar integrated 24-hour guidelines for adults and older adults are currently being developed in Canada to cover the entire lifespan. The sleep duration recommendations contained within the 24-hour movement guidelines can be found in Table 1 .

Although sleep duration recommendations are based on the best available evidence and expert consensus, they are still largely reliant on observational studies using self-reported sleep duration. More longitudinal studies and sleep restriction/extension experiments are needed to better quantify the upper and lower limits of healthy sleep duration, and the shape of the dose–response curve with a wide range of health outcomes. Current sleep duration recommendations also suggest that a generalized optimum exists for the entire population; however, it is unlikely to be the case and this optimum can vary depending on the health outcome examined. 54 There is also inter-individual variability in sleep needs in that sleeping shorter or longer than the recommended amount may not necessarily result in adverse effects on health. For example, genetic differences between individuals can explain some of the variability in sleep needs. However, intentionally restricting sleep over a prolonged period of time (ie, chronic sleep deprivation) is not a good idea and can impact health and safety. 47 Thus, although sleep recommendations are a good tool for public health surveillance, they need to be adapted on a case-by-case basis in clinic (not a one-size-fits-all recommendation).

Sleep duration recommendations have ranges, or zones of optimal sleep, suggesting that the relationship between sleep duration and adverse health outcomes is U-shaped, with both extremities, sleep durations that are too short or too long, associated with negative effects on health. 47 – 51 There is a large body of evidence providing biological plausibility for short sleep as causally related to a wide range of adverse health outcomes; however, the role of long sleep is less clear. Aside from the elderly population, long sleep is generally associated with other health problems (eg, depression, chronic pain, low socioeconomic status) that can confound the associations. 55 , 56 Reverse causation and residual confounding are thus better mechanisms to explain the associations between long sleep and adverse health outcomes. 55 , 56 This may explain why the American Academy of Sleep Medicine and the Sleep Research Society recommends a threshold value for adults (≥7 hours per night) rather than a range (eg, 7–9 hours per night) ( Table 1 ). However, excessive long sleep duration may be informative as it can be indicative of poor sleep efficiency (ie, spending a lot of time in bed but of low quality).

Self-reported sleep duration is typically used in population health surveillance studies, because it provides several advantages (eg, inexpensive, not invasive, and logistically easy to administer to a large sample of individuals). However, the concession is that sleep duration recommendations are then largely based on self-reported data. It is well-known that self-reported sleep duration overestimates actual sleep duration. 57 Thus, it would be misleading to use an objective measure of sleep duration to report the prevalence of short sleepers in a given sample; this would result in an overestimation of true short sleepers. The growing popularity of actigraphy and wearable technologies for health behavior tracking in epidemiology is nevertheless desirable for providing better sleep estimates and more precise associations with health outcomes. 58 , 59 Sleep duration recommendations are also likely to evolve over time, as more objective measures of sleep are used in future studies. For example, an individual self-reporting 7 hours of sleep per night may actually get 6 hours if assessed objectively with actigraphy, as it can better account for total sleep by accurately measuring sleep onset and episodes of night wakings. 60 Thus, using reliable tools for tracking sleep duration over time is important, and one must keep in mind that the overall sleep duration pattern is more critical to long-term health than one snapshot in time (ie, chronic effect vs acute effect of insufficient sleep on health).

Consumers have also become increasingly interested in using fitness trackers and smartphone applications to assess their sleep. These devices provide information on sleep duration and even sleep quality from in-built accelerometry but the mechanisms and algorithms are propriotery. 61 – 64 The growing body of evidence on consumer sleep tracking devices against polysomnography/actigraphy shows that they tend to underestimate sleep disruptions and overestimate sleep duration and sleep efficiency in healthy individuals. 61 – 64 Although consumer sleep tracking devices are changing the landscape of sleep health and have important advantages, more research is needed to better determine their utility and reduce current shortcomings. 61 – 64

Population statistics in Canada indicate that 16% of preschoolers sleep less than recommended, while 20% of children and one-third of teenagers, adults, and older adults report less-than-recommended sleep durations for optimal health. 65 – 67 These nationally representative surveys use subjective data and are thus comparable to the sleep duration guidelines. As shown in Figure 3 , the average sleep duration of Canadians by age group is situated at the lower border of the sleep duration recommendations. On average, a large proportion of Canadians meet the sleep duration recommendations (eg, two-third of teenagers and adults); however, a large number of individuals fail to meet the guidelines (eg, one-third of teenagers and adults). If we dig deeper, we realize that the teenage group has shown the greatest rate of decline in sleep duration in past decades, especially on school days. 11 Knowing the age groups more likely to experience insufficient sleep is critical to help inform the development of interventions aimed at improving sleep (eg, having school start times not earlier than 8:30 am for high-school students). 68 – 70

Sleep duration estimates of Canadians (dashed line) compared with the sleep duration recommendation ranges (solid lines).

Notes: Sleep duration estimates for the Canadian population have been recently published. 65 – 67 However, they are not available for newborns, infants, or toddlers. Canadians sleeping less than recommended for optimal health is estimated at 16% for preschoolers, 20% for school-aged children, 30% for teenagers, 32% for adults, and 31% for older adults.

Ideal amount of sleep: fact or fiction?

As discussed in this article, there is no magic number for all in terms of the ideal sleep amount to obtain each night. Sleep duration recommendations are meant for public health guidance, but need to be individualized to each patient in the clinic. Sleep needs are determined by a complex set of factors, including our genetic makeup, environmental and behavioral factors. For example, high-performance athletes need more sleep to perform at high level and recover from their intense physical training. Sleep needs in children and adolescents can also be driven by their maturation stage, independent of their chronological age. 46 This means that changes in sleep patterns may happen earlier (at a younger age) for some or at an older age for others. Objectively, our current evidence of sleep need is based on circadian, homeostatic, and ultradian processes of sleep regulation and sleep need.

The notion of “optimal sleep” is complex and poorly understood. 71 The definitions of optimal sleep also vary in the literature. It is very often defined as the amount recommended by public health authorities. It has also been defined as the daily amount of sleep that allows an individual to be fully awake (ie, not sleepy), and able to sustain normal levels of performance during the day. 72 Others have also defined it as the amount of sleep required to feel refreshed in the morning. 73 The notion of a new definition to optimal sleep based on performance is of growing interest in the literature. For example, sleep extension interventions have been shown to improve athletic performance. 74 , 75

However, as discussed in this article and by other sleep experts, 76 there is no magic number for optimal sleep, and sleep is influenced by inter- and intra-individual factors. Similarly, in a context of sleep deprivation, individual differences in sleep homeostatic and circadian rhythm contributions to neurobehavioral impairments have been elegantly documented by Van Dongen. 77 – 79

Optimal sleep should be conceptualized as the amount of sleep needed to optimize outcomes (eg, performance, cognitive function, mental health, physical health, quality of life, etc). This implies that there might be many dose–response curves that may differ in shape between outcomes. 54 Typically, the peaks of each health outcome should fall somewhere within the recommended sleep duration range. However, the exact amount of sleep to get each night for optimizing all relevant health outcomes is not straightforward or ubiquitous as the optimal amount for one outcome may not be the same for another outcome (eg, 9 hours of sleep per night could be the ideal for athletic performance, while 7 hours could be the best for academic achievement). Also, determining the causal effects of sleep need on health is not an easy task and requires experiments (eg, interventional study designs with improved vs reduced sleep, both acutely and chronically applied, and then assessing outcomes on physiology, well-being, health, and behavior).

Although the present article focused on sleep duration, many other dimensions of sleep are important beyond getting a sufficient amount each night. These include aspects of sleep quality such as sleep efficiency (ie, proportion of the time in bed actually asleep), sleep timing (ie, bedtime/wake-up times), sleep architecture (ie, sleep stages), sleep consistency (ie, day-to-day variability in sleep duration), sleep consolidation (ie, organization of sleep across the night), and sleep satisfaction. For example, the National Sleep Foundation recently released evidence-informed sleep quality recommendations for individuals across the lifespan. 80 These included sleep continuity variables such as sleep latency, number of awakenings >5 minutes, wake after sleep onset, and sleep efficiency. Along the same lines, monophasic sleep (ie, sleeping once per day, typically at night) is considered the norm in our society but other sleep patterns (eg, biphasic or polyphasic) are also observed depending on the preference of each person or culture. Napping is increasingly seen as a public health tool and countermeasure for sleep deprivation in terms of reducing accidents and cardiovascular events and improving working performance. 81

In summary, there is no magic number or ideal amount of sleep to get each night that could apply broadly to all. The optimal amount of sleep should be individualized, as it depends on many factors. However, it is a fair assumption to say that the optimal amount of sleep, for most people, should be within the age-appropriate sleep duration recommended ranges. Future studies should try to better inform contemporary sleep duration recommendations by examining dose–response curves with a wide range of health outcomes. In the meantime, promoting the importance of a good night’s sleep should be a priority given its influence on other behaviors and the well-known adverse consequences of insufficient sleep. 82 Important sleep hygiene tips include removing screens from the bedroom, exercising regularly during the day, and having a consistent and relaxing bedtime routine.

Acknowledgments

Jean-Philippe Chaput is a Research Scientist funded by the Children’s Hospital of Eastern Ontario Research Institute (ON, Canada).

The authors report no conflicts of interest in this work.

Center for BrainHealth Investigates the Relationship Between Cannabis Use, Sleep and Memory

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Thursday, September 5, 2024

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Francesca Filbey, PhD

Bert Moore Endowed Chair and Professor, School of Behavioral and Brain Sciences Director, Cognitive Neuroscience Laboratory of Addictive Disorders

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The Friends of BrainHealth, a circle of donors supporting the Center for BrainHealth at UT Dallas, awarded four $25,000 Distinguished New Scientists Awards at the annual Friends of BrainHealth Scientist Selection Luncheon recently at the Dallas Country Club. The four scientists will use the funding to lead independently designed research studies.

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What are dreams and why do we have them? New research sheds light on the science behind sleep

Recent breakthroughs are reshaping our understanding of dreams. from lucid dreaming to dream recall, these discoveries are offering fresh insights..

People have pondered whether dreams have a purpose throughout human history. Modern scientists are fascinated with this question too. For a long time the science of dreams has oscillated between fringe research and the mainstream. But creative study designs and new technology are transforming it into an exciting and serious research niche. Here are four recent breakthroughs that may pave the way for a greater understanding of dreaming.

Lucid dreams

In 2021 an international study showed that two-way communication between a lucid dreamer and a researcher in the lab was possible. In 2024, another study built on this by training lucid dreamers to control a virtual car from within their dreams.

The 12 dreamers in the experiment made slight muscle twitches, which sent a signal to a computer to make the virtual vehicle move forwards or turn. Signals were sent back to the dreamer to inform them of obstacles to try and avoid. Some could move the car well, but others, no matter how hard they tried, could not.

While fascinating, it is still unknown how such technology could be used in everyday life. And the small sample of this study, in part owing to the rarity of skilled lucid dreamers, limit the conclusions we can take from it. But the findings suggest that it may be possible (at least with practice) for some people to make decisions from inside a dream and communicate them to the outside world.

Why do we dream?

Sleep and dreams researcher Mark Blagrove from Swansea University thinks dreams were meant to be shared socially and evolved in humans to enhance emotional intelligence and empathy. Since 2016, Blagrove has collaborated with artist Julia Lockheart in a dream discussion and illustration group. An audience member is invited to share a recent dream. Blagrove leads the discussion, while Lockheart sketches an interpretation of the dream onto the pages of Sigmund Freud’s book The Interpretation of Dreams.

His 2019 research paper showed that discussing a dream in this way can lead to increased empathy between dream sharer and listeners. Blagrove argues this could have been valuable to ancestral survival in forming significant connections with others.

Other theories about why we dream have begun to emerge in recent years too, and some were discussed at a panel in June 2024 at the International Association for the Study of Dreams (IASD) annual conference. For example, the embodied cognition theory of dreaming, which proposes that dreams prepare us for the cognitive actions of ordinary waking life. It hasn’t been tested yet but shows a growing scientific interest in the adaptive purpose of dreams.

Insights from long dream series

Michael Schredl of the University of Mannheim in Germany is arguably the most prolific dream researcher today, having published hundreds of articles and books since his career began in the 1990s. He has been keeping a dream journal since the early 1980s. At the IASD conference, he gave a keynote talk analysing over 12,000 of his dreams. Overall, the patterns seemed to support the continuity hypothesis of dreaming - that our dreams are influenced by events and concerns that are happening in our waking lives.

Schredl believes he is one of the first people to look at weather patterns in dreams. He noticed a steady decline over the years of ice, snow and hail in his dreams. Interestingly, this was similar to the documented declining number of “ice days” (days when the temperature was below 0°C for 24 hours) in Germany since he has been keeping a dream journal. He joked that perhaps the global warming effects are showing up in dreams too, but this could also be influenced by waking concerns about such things.

Another interesting pattern was references to money in dreams. When the Deutsche Mark was the prevailing currency, it occasionally showed up in his dreams over the years, but when the German currency changed to the Euro in 2002, the number of Deutsche Mark references were replaced by references to the Euro. Long dream series such as this are rare, but they can show how us how intertwined dream content is with our waking lives.

Dream recall

Some people are better at remembering their dreams than others, recalling dreams more frequently and in more detail. For a long time, researchers have tried to determine the reasons and mechanisms for this difference. They’ve looked into factors including personality and attitude towards dreams, general memory ability, and the small physiological signals that happen during certain sleep stages. So far, one of the most consistent predictors of more frequent dream recall has been a positive attitude towards dreaming; if you think dreams are important, you’re probably more motivated to try and remember them more often.

In 2022 French researcher Salomé Blain and their colleagues investigated the role of attention in dream recall, a cognitive skill which is closely connected to memory. While their participants’ ability to recall dreams did not seem linked to working memory - which temporarily holds information for immediate use - participants with low dream recall were better at ignoring distracting stimuli, and vice versa.

They compared low and high dream recallers in their ability to distinguish whether two melodies (which were both played in the same ear) were different, while a distracting melody was played in the opposite ear. This suggests that people who are good at remembering dreams may be worse at filtering out irrelevant and distracting information, hence they may notice more of what’s happening in their mind while sleeping. However, dream recall is a learnable skill. For example, keeping a dream journal can significantly improve dream recall, especially for people who already have quite low dream recollection.

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