[Association of sleep duration and risk of frailty among the elderly over 80 years old in China: a prospective cohort study].

Objective: To explore the association between sleep duration and the risk of frailty among the elderly over 80 years old in China. Methods: Using the data from five surveys of the China Elderly Health Influencing Factors Follow-up Survey (CLHLS) (2005, 2008-2009, 2011-2012, 2014, and 2017-2018), 7 024 elderly people aged 80 years and above were selected as the study subjects. Questionnaires and physical examinations were used to collect information on sleep time, general demographic characteristics, functional status, physical signs, and illness. The frailty state was evaluated based on a frailty index that included 39 variables. The Cox proportional risk regression model was used to analyze the correlation between sleep time and the risk of frailty occurrence. A restricted cubic spline function was used to analyze the dose-response relationship between sleep time and the risk of frailty occurrence. The likelihood ratio test was used to analyze the interaction between age, gender, sleep quality, cognitive impairment, and sleep duration. Results: The age M (Q₁, Q₃) of 7 024 subjects was 87 (82, 92) years old, with a total of 3 435 (48.9%) patients experiencing frailty. The results of restricted cubic spline function analysis showed that there was an approximate U-shaped relationship between sleep time and the risk of frailty. When sleep time was 6.5-8.5 hours, the elderly had the lowest risk of frailty; Multivariate Cox proportional risk regression model analysis showed that compared to 6.5-8.5 hours of sleep, long sleep duration (>8.5 hours) increased the risk of frailty by 13% (HR: 1.13; 95%CI: 1.04-1.22). Conclusion: There is a nonlinear association between sleep time and the risk of frailty in the elderly.