Campbell SS, Stanchina MD, Schlang JR, Murphy PJ. Effects of a month-long napping regimen in older individuals. J Am Geriatr Soc. 2011;59:224-232.
Open, observational study using 3 laboratory sleep sessions and 2-week, at-home recordings in between. Comparison of 45-minute (short nap) versus 2-hour (long nap) times on nighttime sleep and waking function over 1 month. Assessment of compliance to such a napping regimen was also assessed.
22 participants (11 men, 11 women) from 50 to 83 years old (mean=70 years old). Although recruitment was open to those without sleep problems, all subjects reported age-related sleep disturbance in maintenance or duration of sleep. No subjects had overt sleep disorders (eg, apnea, restless leg syndrome, circadian rhythm sleep disorder), as this was used as exclusionary criteria. Participants did not nap regularly at the time of enrollment.
Objective and subjective measures were used to assess participants, including polysomnography (sleep EEG), actigraphy, sleep diaries, neurobehavioral performance, and sleep latency tests.
When pooled, both the short- and long-nap groups averaged more than 5 naps per week, although there was a lot of individual variability. Napping did not affect nighttime sleep. Using both groups nighttime sleep duration averaged 7:57 ± 1:22 hours on days with naps, versus 8:06 ± 1:49 hours after nap-free days. Sleep quality (ie, sleep onset latency, sleep efficiency, sleep architecture) was unchanged by napping in either group. Neurobehavioral performance improved in both groups for 3 out of 4 tasks measured. Lastly, there was an increase in total, 24-hour sleep time, and a resultant decrease in daytime sleepiness in both groups versus individual baseline levels. Compliance was more favorable for the short-nap group versus the long-nap group.
Napping in the mid-day is a custom in many cultures throughout the world. Whether such naps affect nighttime sleeping patterns by lessening the duration or quality of nighttime sleep has been debated. This study suggests that nighttime sleep duration and quality are not impaired by regular napping. This is in keeping with a 2005 publication by the same authors showing that the amount of sleep in a 24-hour period can be improved through adding a daytime nap, and that this may improve waking function.1 While napping is not a cultural norm in America, there have been numerous studies showing that napping, particularly in the elderly, may improve overall function.2,3,4
The authors postulate that the stress-relieving properties of napping may have a role, and that working men may derive more benefit due to greater stress reduction.
Other studies have shown that napping in the afternoon may have a greater impact than merely improving day-to-day functional performance. Dr. Androniki Naska studied 23,681 Greek men and women (ages 20–86) and found that over the 6-plus-year follow-up, individuals who took naps had a 34% lower risk of dying from heart disease than those who did not nap. This difference was greatest among working men who took naps, with a 64% lower risk of death from heart disease versus a 36% reduction in non-working men.5 The authors postulate that the stress-relieving properties of napping may have a role, and that working men may derive more benefit due to greater stress reduction.
While the majority of studies on daytime napping have had favorable results, a few have raised the question of whether napping is universally beneficial. In a fairly large study of 8,101 Caucasian women (<69 years old) tracked over a 7-year period, women who reported daily napping were 44% more likely to die from any cause and 58% more likely to die from cardiovascular causes than non-napping women.6 In this same study, those women reporting 9–10 hours of sleep in 24 hours had a greater risk of all-cause mortality versus those sleeping 8–9 hours. Of note, these correlations were not significant if weekly naps totaled less than 3 hours, suggesting very short naps have no correlation. There was no indication as to whether psychological factors such as depression were factored into the study.
A community-based study done in Guangzhou, China, showed a correlation between daytime napping and the development of type 2 diabetes. The participants, 19,567 Chinese men and women, completed a self-reported frequency-of-napping questionnaire. Diabetes was assessed through blood glucose or reports of physician-directed diagnosis or treatment. Those who reported napping 4–6 times per week had a 42% greater risk of developing type 2 diabetes, and those reporting daily naps had a 52% increase. This association was also found between napping and impaired glucose utilization. Adjustments for confounding factors such as demographics, lifestyle and sleep habits, health status, adiposity, and metabolic markers did not change the significance of the association.7 Whether this data can be extrapolated to other, more heterogeneous genetic populations remains unknown. However, elucidation of this association should be pursued as the prevalence of type 2 diabetes in China is rising rapidly.
Of course, association and causation are not equal, and while the observational studies showing possible detriment should be taken into consideration, there may be possible underlying factors, such as genetic predisposition or more napping in those with depression, that were not taken into account. Nonetheless, it appears that shorter duration of naps and napping in those that are otherwise healthy (ie, no overt sleep depriving diagnosis) is safe, and possibly beneficial for our patients. A cautionary note for those of Chinese descent is prudent, and perhaps maintaining “normal” total number of hours at 8 hours of total sleep per 24-hour cycle can lessen any possible risk for our post-menopausal population.
In the study, it is possible that the improved neurobehavioral performance in both groups may have been due to repeat exposure of the testing since there was little correlation with 24-hour sleep times. This study was only 1 month in duration, so it is possible that further improvements or different results may emerge over a longer time course. Of course, none of these participants had overt sleep disorders, thus no extrapolation of this data can be made for those patients with sleep disorders. This study was small—only 22 subjects—so repeating such a study on a larger scale would be necessary to substantiate these findings.