Sleep has a major impact on cognitive function in older adults, as a 6 to 7 hour night sleep is associated with optimal cognitive function in middle-aged adults and an afternoon nap of less than 30 minutes is important for older people, according to published study results is in the Journal of Affective Disorders.
While previous studies have confirmed the significant impact of sleep on cognitive function, optimal sleep patterns are not well established. The study’s researchers attempted to examine these sleep strategies as well as the underlying mechanisms.
This cross-sectional study is based on data from the China Health and Retirement Longitudinal Study (CHARLS), a nationally representative longitudinal study of residents of residential communities in China who are at least 45 years old. Of 17,708 respondents who took part in the national survey between 2011 and 2012, the study researchers included a sample of 6207 participants (mean age 57.85 years; men 51.39%) with available data on night sleep and afternoon nap. The night sleep was divided into 5 groups (≤ 5.0 h, 5.1-6 h, 6.1-7 h, 7.1-8 h,> 8 h), as was the sleep pattern in the afternoon (0 min, <30 min, 31-60 min) 61-120 min, 121 min).
Participants with a night sleep of 6.1 to 7 hours had the highest recognition scores and the difference from all other groups was statistically significant (P <0.05). In addition, participants with an afternoon nap of less than 30 minutes had the highest recognition scores (P <0.05). The synergistic effect of night and afternoon nap was not significant.
When the mediating role of inflammation in sleep and in cognitive association was examined, the results indicated a significant association between night sleep with white blood cells (P = 0.01) but not with the highly sensitive C-reactive protein. There was a significant association between afternoon nap with white blood cells (P = 0.00) and the highly sensitive C-reactive protein (P = 0.02).
The white blood cell count was lower in the 6.1-7 hour group compared to all other groups. The data suggest that sleep plays a key role in the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis, both of which can have a significant impact on inflammatory gene expression.
The study had several limitations, including cross-sectional design, use of self-reported data, lack of data from sleep questionnaires or objective measurements, and limited data on inflammation.
“We found that sleeping six to seven hours at night and less than 30 minutes in the afternoon were optimal for cognitive function in middle-aged and elderly people. The association between sleep and cognition is also partly influenced by white blood cells. However, we could not find a significant synergistic effect of night sleep and afternoon nap on cognitive function, ”concluded the researchers of the study.
Hu M, Shu X, Feng H, Xiao LD. Sleep, Inflammation, and Cognitive Function in Middle-Aged Adults and Older Adults: A Population-Based Study. J Afford influence. 2021; 284: 120-120 125. doi: 10.1016 / j.jad.2021.02.013