Data from a cohort of more than 8000 participants suggest that older adults with less optimal sleep duration might benefit from moderate napping for their cognitive functions.
Using middle-aged and older adults from the China Health and Retirement Longitudinal Study, findings from a recently published paper showed that moderate amounts of napping, between 1-30 minutes, can protect against the negative effects of short or long sleep duration on episodic memory.
All told, over a 7-year follow-up, for participants with shorter sleep duration, both non-napping (ß = –0.03; P = .017) and longer napping (ß = –0.04; P = .018) were associated with a significantly faster decline of episodic memory. Additionally, those with both non-napping and longer sleep duration also had a significantly greater decline (ß = –0.07; P = .003) in episodic memory scores.
In the conclusion of the study, senior investigator Bin Yu, PhD, associate professor, Tianjin University, and colleagues noted that, "Our results implied that those older adults who have a less optimal sleep duration might benefit from moderate napping for their cognitive functions. These findings may provide new insight into the prevention of dementia through better sleep management."
The analysis included 8107 participants aged 45 and older who had complete baseline data and at least 1 reassessment of cognitive function over the follow-up period. In terms of measures, cognition was assessed through CHARLS, a 2-part tool that evaluates episodic memory and mental status. Visuospatial ability was assessed by accurately redrawing a previously shown picture, and numeric ability was assessed by serial 7 subtraction from 100.
Sleep variables, such as nap time and nighttime sleep duration, were obtained through a self-administered questionnaire. Afternoon napping duration was assessed by asking, “During the past month, how long did you take a nap after lunch in general?” Patients were categorized as either non-nappers (0 min; n = 3626), moderate nappers (1-30 min; n = 1403), and long nappers (>30 min; n = 3078). Patients were then categorized on sleep duration, split into groups of either short sleep (<7 hrs; n = 3990), normal sleep (7-8 hrs; n = 3522), and long sleep duration (>8 hrs; n = 595).
Demographically, participants with moderate napping were more likely to be employed, lived in an urban area and participate in social activities, had a higher education level, were more likely to have chronic diseases, and were less likely to be current smokers. Moderate nappers, which made up 17.3% of the cohort, were more likely to have higher episodic memory and mental status than the other 2 groups. Notably, those with normal nighttime sleep were more likely to have higher episodic memory and mental status scores than the other 2 groups.
In the cross-sectional analysis, findings showed that participants who did not nap had lower mental status scores (ß = –0.17; P = .003) and lower episodic memory scores (ß = –0.09; P = .042) than the reference group. Additionally, participants with shower (ß = –0.09; P = .044) and longer sleep duration (ß = –0.42; P <.001) had lower mental status scores as compared with the reference group. Longitudinally, investigators identified a significant interaction between sleep duration and time for the shorter sleep group, which indicated that those with shorter sleep duration have greater decline in episodic memory scores over time relative to those with normal sleep duration.
Yu et al wrote, "Among the strengths of this study are its relatively large sample size, prospective design and investigation of a dynamic trajectory of cognition over 7 years using a series of objective tests." Despite this, there were several limitations to the study, including the fact that other sleep or napping-related characteristics that might be associated with cognitive function, were not available in CHARLS. Additionally, the study did not capture information on the timing or frequency of napping, and assumed that afternoon napping was taken routinely.
Over the 7-year period, individuals with both non-napping and shorter sleep duration had significantly lower episodic memory scores (ß = –0.12; P = .046). Both longer napping and longer sleep duration had lower episodic memory scores (ß = –0.23; P = .020); however, regardless of the napping duration, those who sleep longer had lower mental status scores (>8 hrs, 0 min nap: ß = –0.55; P <.001; >8 hrs, 1-30 min nap: ß = –0.57; P = .008; >8 hrs, >30 min nap: ß = –0.36; P = .009).