Excessive sleep increased the risk of incidence of cognitive impairment among older Chinese adults: a cohort study based on the Chinese Longitudinal Healthy Longevity Survey (CLHLS)

Abstract

Study objectives: Based on a cohort from the Chinese Longitudinal Healthy Longevity Survey (CLHLS), we aimed to evaluate the relationship between sleep duration and the incidence of cognitive impairment among older Chinese adults. Methods: We conducted a prospective analysis based on 3692 participants from the CLHLS at baseline (in 2011), and as a 3-year follow-up (till 2014), 531 participants (14.4%) had cognitive impairment, which was defined as a Mini-Mental State Examination score <24. Sleep duration was classified into three groups: short (≤5 hours/day), normal (>5 but <10 hours), and long (≥10 hours/day). A logistic regression model was used to examine the association between baseline sleep duration and cognitive impairment after adjusting for sociodemographic data, living habits, and health conditions. Results: Five hundred sixty-two participants (15.2%) were in the short-duration group, and 608 participants (16.5%) were in the long-duration group. After adjusting for multiple potential confounders, compared with normal sleep duration, long sleep duration was associated with the incidence of cognitive impairment (OR = 1.309, 95% CI: 1.019–1.683), especially among men (OR = 1.527, 95% CI: 1.041–2.240) and those having a primary and above education level (OR = 1.559, 95% CI: 1.029–2.361). No significant association was observed between short sleep duration and cognitive impairment (OR = 0.860, 95% CI: 0.646–1.145). Conclusions: Excessive sleep may increase the risk of cognitive impairment in older individuals. It may be a suggestive sign of early neurodegeneration and may be a useful clinical tool to identify those at a higher risk of progressing to cognitive impairment.

The importance of diversity in aging studies

“…The current study noted that among individuals with primary and above education, excessive sleep duration was linked to cognitive impairment (Zhang et al, 2021). Education may contribute to 'cognitive reserve' or the capacity of the brain to buffer against age-related decline and pathologic damagethus delaying the onset of noticeable clinical symptoms (Stern, 2012).…”

“…In conclusion, the Zhang et al (2021) study and the diverse cohort of older Chinese study participants provide an important contribution to the growing knowledge regarding sleep duration and cognitive impairment. However, further exploration of education, language, and lifespan changes are warranted to establish these causal factors and identify which individuals would be most likely to benefit from potential preventative sleep-related interventions or use of sleep as an early risk factor for future cognitive impairment.…”

“…One particular challenge of studying older adults in China is geographic and socioeconomic heterogeneity. The Zhang et al (2021) study included participants from the majority of China's province and considered the diversity of environment and education in their analyses. Zhang and colleagues found education and rural living to be associated with cognitive impairment for long sleepers in this study.…”

“…Similar to tracking cognition, future studies may benefit from tracking sleep over a longer period of time or over individual's lifespan. Like most large cohort studies, the Zhang et al (2021) study used self-report measures of sleep duration at baseline, and did not capture sleep duration across the lifespanthus it is unclear if sleep duration during childhood, young adulthood, or middle age would be linked to future cognitive decline as well. Alterations in sleep may also be linked to aging milestones such as having young children or retirement.…”

Put more attention to dementia knowledge changes among minority

“…However, as we mentioned above, the public education has shift to dementia prevention and early detection, newly identified risk factors should be taken into consideration. For example, Zhang et al found that excessive sleep ( ≥ 10 hours/day) may increase the risk of cognitive impairment in older individuals (OR = 1.309, 95% CI: 1.019-1.683) (Zhang et al, 2022). To overcome the shortcoming of the structure questionnaire, the qualitative design might be considered in future studies, which could provide a more detailed description of participants' perceptions, thoughts, and understandings of dementia.…”