Association of nocturnal sleep duration and nocturnal sleep changes with instrumental activities of daily living disability among middle-aged and elderly Chinese

To investigate the association of baseline nocturnal sleep duration and sleep changes with functional disability in middle-aged and elderly Chinese.Data for this study were collected from the China Health and Retirement Longitudinal Study (CHARLS) from baseline (2011) to the Wave 3 follow-up (2018). 8361 participants free of IADL disability in 2011 and aged ≥ 45 years old were recruited and prospectively followed till 2018 to analyze the association between baseline nocturnal sleep duration and IADL disability. Of these 8361 participants, a total of 6948 participants had no IADL disability at the first three follow-up visits and completed the 2018 follow-up to analyze the association between nocturnal sleep changes and IADL disability. Nocturnal sleep duration (hours) was self-reported at baseline. The coefficient of variation (CV) of nocturnal sleep duration at baseline and three follow-up visits was used to calculate sleep changes and classified into mild, moderate, and severe degrees by the quantiles. Cox proportional hazards regression model was used to analyze the association of baseline nocturnal sleep duration with IADL disability, and the binary logistic regression model was used to analyze the association of nocturnal sleep changes with IADL disability.Among the 8361 participants of 50237.5 person-years follow-up with a median follow-up of 7 years, 2158 (25.81%) participants developed IADL disabilities. Higher risks of IADL disability were observed among participants with sleep duration <7 h [HR(95%): 1.23(1.09-1.38)], 8∼<9 h [HR(95%): 1.05(1.00-1.32)] and ≥9 h [HR(95%): 1.21(1.01-1.45)] compared to those with 7∼<8 h. Among the 6948 participants, a total of 745 (10.72%) participants finally developed IADL disabilities. Compared with mild nocturnal sleep changes, moderate [OR(95%): 1.48(1.19-1.84)] and severe [OR(95%): 2.43(1.98-3.00)] sleep changes increased the probability of IADL disability. The restricted cubic spline model showed that a higher degree of nocturnal sleep changes was associated with a greater probability of IADL disability.Both insufficient and excessive nocturnal sleep duration were associated with higher risk of IADL disability in middle-aged and elderly adults, independent of the participants' gender, age, and napping habits. Higher nocturnal sleep changes were associated with a higher probability of disability in IADL. These findings highlight the importance of appropriate and stable nocturnal sleep, and the need to pay attention to population differences in the impact of nocturnal sleep duration on health.