Sleep has a major impact on cognitive function in older adults, as nighttime sleep of 6 to 7 hours is associated with optimal cognitive function in middle-aged adults and afternoon napping of less than 30 minutes is important for older people, according to study results published in Journal of Affective Disorders.
While previous studies have supported the significant impact of sleep on cognitive function, the optimal sleep patterns are not well-established. Study researchers sought to investigate these sleep strategies as well as the underlying mechanisms thereof.
This cross-sectional study was based on data from China Health and Retirement Longitudinal Study (CHARLS), a nationally representative longitudinal study of Chinese community-dwelling residents of at least 45 years old. Of 17,708 respondents who participated in the national survey during 2011-2012, study researchers included a sample of 6207 (mean age, 57.85 years; men, 51.39%) participants with available data on nighttime sleep and afternoon napping their analysis. Nighttime sleep was categorized into 5 groups (≤5.0 h, 5.1-6 h, 6.1-7 h, 7.1-8 h, >8 h), as were the afternoon sleep patterns (0 min, <30 min, 31-60 min, 61-120 min, 121- min).
Participants with nighttime sleep of 6.1 to 7 hours had the highest cognition scores and the difference compared with all other groups was statistically significant (P <.05). Furthermore, participants with afternoon napping of less than 30 min had the highest cognition scores (P <.05). The synergistic effect of nighttime sleep and afternoon napping was not significant.
When the mediating role of inflammation in sleep and cognition association was investigated, the results suggested a significant association between nighttime sleep with the white blood cell (P =.01), but not with high-sensitivity C-reactive protein. There was a significant association between afternoon napping with the white blood cell (P =.00) and high-sensitivity C-reactive protein (P =.02).
White blood cell count was lower in the 6.1-7 h group, compared with all other groups. The data suggest that sleep has a key role in the sympathetic nervous system and the hypothalamus-pituitary-adrenal axis, both of which can have a significant impact on inflammatory gene expression.
The study had several limitations, including the 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 nighttime sleep of six to seven hours and afternoon napping of lower than 30 minutes were optimal for cognitive function in middle-aged and older people. Also, the sleep-cognition association is partly affected by the white blood cell. However, we did not find the significant synergistic effect of nighttime sleep and afternoon napping on cognitive function,” concluded the study researchers.
Hu M, Shu X, Feng H, Xiao LD. Sleep, inflammation and cognitive function in middle-aged and older adults: A population-based study. J Affect Disord. 2021;284:120-125. doi:10.1016/j.jad.2021.02.013