Nighttime sleep duration, daytime napping, and metabolic syndrome: findings from the China Health and Retirement Longitudinal Study

Purpose: This study aimed to assess the association between nighttime sleep, daytime napping, and metabolic syndrome (MetS) in an elderly Chinese population. Methods: A cross-sectional study was conducted using data from the 2011 China Health and Retirement Longitudinal Study (CHARLS) to examine the association between nighttime sleep, daytime napping, and MetS (defined according to the Chinese Diabetes Society criteria). Sleep duration was assessed by a self-reported questionnaire. Binary logistic regression models were used to estimate odds ratios and 95% confidence intervals of the associations adjusting for covariates. Results: Among 4785 elderly Chinese aged over 65 years old, there was no association between short-time sleep duration (< 7 h/day) and MetS. However, long-time sleep duration (> 8 h/day) decreased the odds of MetS by 53% (aOR= 0.47; 95% CI 0.23–0.96) compared to normal sleep duration (7–8 h/day). Compared to no daytime napping, short-time napping (≤ 30 min/day) was associated with increased odds of MetS (aOR = 1.55, 95% CI 1.02–2.36) and long-time napping (> 30 min/day) was associated with even higher odds of MetS (aOR = 1.77, 95%CI 1.24–2.53). Individuals who were over 75 years old, with elementary school education, and good health status had lower odds of MetS, while women, individuals living in rural areas, and those who reported poor health status had higher odds of MetS. Conclusion: Long-time sleep duration decreased and daytime napping increased the risk of MetS among the elderly Chinese population. We speculate that increasing nighttime sleep duration and decreasing daytime napping may help reduce the risk of MetS.