Self-reported napping was quite common in this group of sedentary, community-dwelling older adults with impaired physical performance. The finding that 54 percent of older adults napped at least once a week is within the range that others have reported.8,26,35,36
Currently, not all sleep studies routinely ask about nap behaviors. This study adds further supporting evidence that the prevalence of napping in older adults is high, and clearly must be accounted for in sleep studies involving older adults.
This study failed to show a clear association between age and napping, unlike others who have shown that the prevalence of napping increases with age.1,26,29,37
This difference could be explained by the fact that our population had a more narrow range of ages, focusing on the “oldest” old (70–89 years), while others have compared napping behavior between “younger” old (50–60 years) and “oldest” old (70–80 years). Men napped significantly more than women, which has been noted by others.1,26,38,39,40
While few studies have looked specifically at napping and race, our results suggest that African Americans nap more than other racial groups, a finding reported in two other studies.41,42
Reported poor sleep was not more prevalent in nappers versus non-nappers. There was no difference between nappers and non-nappers in terms of reported nighttime sleep duration, sleep-onset latency, or sleep efficiency. This finding is consistent with others,7,29
one of which used objective measures to show that daytime sleep was not related to nocturnal sleep in post-menopausal women. While self-reported napping did not have a negative effect on reported nighttime sleep as we had hypothesized, there is a speculation that napping may actually be a compensation for daytime sleepiness incurred from fragmented nighttime sleep. Sleep apnea43
or sleep fragmentation due to nocturia10,44,45
are two prevalent conditions that may not be reported as detracting from nocturnal sleep duration and quality but may still contribute to daytime sleepiness and thus increase the propensity to nap. A recent population based study suggested that napping could be regarded as a marker of sleep apnea, which could account for the incidence of cardiovascular diseases observed in nappers. Data in that study showed that nappers had a higher frequency of sleep apnea compared to controls at three different cutoff points.46
In addition, a study of female insomniacs showed that habitual nap behavior was not related to subjective or objective measures of nocturnal sleep but was rather indicative of their daytime sleepiness.47
This may be suggested by our finding that nappers spent 10 percent of 24-hour sleep occupied in napping, despite having no significant difference in nocturnal sleep parameters as compared to non-nappers.
In this cohort, napping was more prevalent in those with diabetes mellitus. The diagnosis of diabetes mellitus and higher BMI were also associated with longer nap duration. This finding provides a new piece of evidence that diabetes mellitus has an effect on daytime sleep. Others have described poor nighttime sleep in diabetics, particularly with respect to altered sleep durations48
and sleep disordered breathing,49,50
along with higher rates of insomnia, hypnotic medication use, and daytime sleepiness compared to controls. Studies correlating diabetes mellitus with increased daytime sleepiness have shown that daytime sleepiness was greatest in those with frequent nocturnal micturition episodes, somewhat explained by increased sleep apnea syndrome. Further study with objective actigraphy or polysomnography measurements of nighttime sleep and napping behavior is required to address such hypotheses.
A limitation to this study is the lack of a full sleep habits inventory or polysomnography. Given the nature of this ancillary study, within the larger framework of its parent study, we were limited by participant burden to a subset of questions from the PSQI that were previously shown to be prevalent in older adults recruited for exercise trials and responsive to a physical activity intervention.51
Therefore, we cannot address the potential importance of primary sleep disorders as potential correlates of napping. However, our finding of an association of napping with obesity and diabetes implicates sleep apnea and thus nocturnal arousals as a possible cause. Finally, a possible confounding variable not defined in our study was medication usage, especially hypnotics. Some reports do not show a correlation of hypnotics with daytime sleepiness while others have shown correlations of these medications with disturbed sleep11,52
and napping status.
Self-reported sleep disorders are poorly correlated with polysomnography. Ideally, objective measures of nighttime sleep as well as napping should be used in future research. Recent studies, using objective assessment show under-reporting of napping behavior when compared to actigraphy and polysomnography measurements.8,29
It remains unclear whether napping should be an endorsed or discouraged practice, with reports that a short nap may be beneficial to cognitive status1,23,24,25
while others reporting that napping increases mortality rate.9,11,12
Our study provides further evidence that napping is a common practice of older adults and does not appear to worsen nighttime sleep. We provide evidence that napping behavior should always be assessed in sleep studies of older adults. It is also important for clinicians to ask about napping behavior and determine its relationship to daytime sleepiness and nighttime sleep before making clinical recommendations.
In summary, this is one of the first studies to show that those with diabetes have a higher risk of napping and subsequently sleep longer when day and nighttime sleep are considered together. It may be suggested that napping is an indicator of silent co-morbid disease complications. In our study population, nappers had a higher prevalence of diabetes mellitus, while cardiovascular disease has been extensively cited in the literature to be associated both with napping and daytime sleepiness, particularly in myocardial infarction survivors.17,18,19,20,21
While it remains unclear whether illness might increases actual sleep need, older individuals who are sicker may report more sleep per day due to an increase in their subjective need for sleep. As illness often reduces nighttime sleep quality, daytime napping may be an important mechanism for addressing their desire for more sleep.