I was invited to a cardiology conference to talk about sleep, specifically the benefits of napping for health and cognition. After the talk, along with the usual questions related to my research, the cardiac surgeons in the room shifted the conversation to better resemble a group therapy session, sharing their harrowing personal tales of coping with sleep loss on the job. The most dramatic story involved a resident in a military hospital who, unable to avoid the effects of her mounting sleep loss, did a face plant into the open chest of the patient on the surgery table.
Yet humans generally do not get sufficient sleep, and a growing body of research indicates that this deficit is taking a toll on day-to-day functioning, as well as long-term health outcomes. Epidemiology studies have associated insufficient sleep with increased disease risk, including cardiovascular and metabolic disease, diabetes, cancer, Alzheimer’s disease and related dementias, as well as early mortality. Laboratory studies that experimentally restrict sleep show deficits across many cognitive domains, including executive functions, long-term memory, as well as emotional processing and regulation. Insufficient sleep in adolescents can longitudinally predict depression, thought problems, and lower crystallized intelligence, as well as structural brain properties. In older adults, it can predict the onset of chronic disease, including Alzheimer’s disease. Repeated nights of insufficient sleep (eg, three to four nights of four to six hours of sleep) have been shown to dysregulate hormone release, elevate body temperature and heart rate, stimulate appetite, and create an imbalance between the two branches of the autonomic nervous system by prolonging sympathetic activity and reducing parasympathetic restorative activity.
Given this ever-increasing list of ill effects of poor sleep, the quest for an effective, inexpensive, and manageable intervention for sleep loss often leads to the question: What about naps? A nap is typically defined as a period of sleep between five minutes to three hours, although naps can occur at any hour, they are usually daytime sleep behaviors. Between 40% and 60% of adults nap regularly, at least once a week, and, excluding novelty nap boutiques, they are free of charge and require little management or oversight. Yet, for all their apparent positive aspects, the jury is still out on whether naps should be recommended as a sleep loss countermeasure due to the lack of agreement across studies as to their effects on health.
Naps are studied in primarily two scientific contexts: laboratory experimental studies and epidemiological studies. Laboratory experimental studies measure the effect of short bouts of sleep as a fatigue countermeasure or cognitive enhancer under total sleep deprivation, sleep restriction (four to six hours of nighttime sleep), or well-rested conditions. These experiments are usually conducted in small (20 to 30 participants) convenience samples of young adults without medical and mental health problems. Performance on computer-based cognitive tasks is tested before and after naps of varying durations. By varying nap durations, researchers can test the impact of specific sleep stages on performance improvement. For example, in well-rested, intermediate chronotype individuals, a 30-minute nap between 13:00 and 15:00 will contain mostly stage 2 sleep, whereas a nap of up to 60 minutes will include slow wave sleep, and a 90-minute nap will end on a bout of rapid eye movement sleep. Studies that vary nap duration and therefore sleep quality have demonstrated an important principle of sleep’s effect on the brain and cognitive processing, namely that each sleep stage uniquely contributes to different aspects of cognitive and emotional processing. And that when naps are inserted into a person’s day, even in well-rested conditions, they tend to perform better after the nap than if they had stayed awake. Napping leads to greater vigilance, attention, memory, motor performance, and creativity, among others, compared with equivalent wake periods.1,2 Compared with the common fatigue countermeasure—caffeine—naps enhance explicit memory performance to a greater extent.
Sara C. Mednick, PhD
In the second context, epidemiological studies examining the impact of napping on health outcomes are typically conducted in older, less healthy, less active populations who tend to have poorer eating habits, multiple comorbidities, psychological problems, and a wide range of socioeconomic status. The strength of this approach is the sample size, which allows for correlations between factors on a large scale while providing enough data to hopefully control for possible confounds (eg, demographics, SES, exercise and eating habits, comorbidities). However, as the data were usually collected by a different group with different goals than the current epidemiologist exploring the data, there can be a disconnect between the current study goals and the variables that were initially collected by the original research team. As such, the current researcher is left with a patchwork of dissimilar variables that they must find a way to organize to answer the current question.3
When applied to the question of health effects of napping, epidemiology researchers typically divide the population into two groups, either based on a yes or no response to a napping question, or a frequency score where those who indicate napping more than one, two, or three times a week are distinguished as nappers compared to non-nappers who don’t meet these criteria. As the field lacks standard definitions for categorizing nap behavior, it is left to the discretion of the researcher to make these decisions. Furthermore, there is usually little other information collected about napping habits that could be used to better characterize napping behavior, such as lifetime nap habits, intentional vs accidental napping, and specific motivations for napping. These secondary factors have been shown to significantly moderate the effects of napping in experimental studies.
Considering the challenges, it is not surprising that there is wide disagreement across studies as to the health effects of napping.4 On the negative side, some studies have demonstrated that napping leads to increased risk of cardiovascular disease, dementia, and mortality.5-7 On the positive side, large cohort studies that control for some of these limitations report that habitual napping can predict better health outcomes, including lower mortality risk, reduced cardiovascular disease, and increased brain volume.8,9 Furthermore, age complicates matters as recent studies in older adults report that more frequent napping may be associated with reduced propensity for sleep during morning hours, and late afternoon naps were associated with earlier melatonin onset and increased evening activity, suggesting greater circadian misalignment in nappers and strategic use of napping as an evening fatigue countermeasure. More frequent napping in older adults was also correlated with lower cognitive performance in one of three cognitive domains. These results implicate more frequent and later-in-the-day napping habits in older adults may indicate altered circadian rhythms and reduced early morning sleep, with a potential functional impact on memory function. However, the same cautionary note applies to these studies, as few nap characteristics were reported that would help interpret the study outcomes and guide recommendations.10 Thus, the important and timely question of whether napping should be recommended does not, as of yet, have an answer. For clinicians weighing the multidimensional factors associated with napping in efforts to give a considered response to their patients, I can offer a set of questions that may help with tailoring responses to each individual. A lifetime history of napping can be an indicator of a health-promoting behavior, whereas a relatively recent desire to nap may reflect an underlying comorbidity that increases fatigue, sleepiness, and unintentional daytime sleep. Motivation for napping can also be revealing, as the desire to nap may be masking symptoms of depression and anxiety.11 Nighttime sleep disturbance may promote napping or, in some cases, arise from too much napping and should always be considered as a primary health measurement. In conclusion, it’s important to recognize the significance of addressing nighttime sleep disturbance and the potential impact of napping on overall health. For many, napping can be an essential and potent habit that can be encouraged throughout the lifespan for its salutary influences.
References
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2. Jones BJ, Spencer RMC. Role of Napping for Learning across the Lifespan. Curr Sleep Med Rep. 2020 Dec;6(4):290-297. Doi: 10.1007/s40675-020-00193-9. Epub 2020 Nov 12. PMID: 33816064; PMCID: PMC8011550.
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6. Stang A, Dragano N., Moebus S, et al. Midday naps and the risk of coronary artery disease: results of the Heinz Nixdorf Recall Study Sleep, 35 (12) (2012), pp. 1705-1712
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9. Paz V, Dashti HS, Garfield V. Is there an association between daytime napping, cognitive function, and brain volume? A Mendelian randomization study in the UK Biobank. Sleep Health. 2023 Oct;9(5):786-793. Doi: 10.1016/j.sleh.2023.05.002. Epub 2023 Jun 20. PMID: 37344293.
10. Mednick SC. Is napping in older adults problematic or productive? The answer may lie in the reason they nap. Sleep. 2024 May 10;47(5):zsae056. doi: 10.1093/sleep/zsae056. PMID: 38421680; PMCID: PMC11082470.
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