This study aimed to investigate the association between bedtime and cardiac autonomic function in older adults. This cross-sectional study included community-dwelling older adults aged ≥ 65 years. Self-reported bedtime was categorized as early (< 21:30), intermediate (21:30-22:30), and late (> 22:30). Cardiac autonomic function was evaluated by HRV. The lowest tertiles for each HRV parameter were defined as unhealthy indicators. A total of 3,729 individuals participated, with mean age of 76.3 ± 6.6 years. After controlling for various covariates, late bedtime was associated with a lower risk for unhealthy total power [Odds ratio (OR) = 0.74; 95% confidence interval (CI) = 0.59-0.93] and low frequency power (OR = 0.69, 95% CI = 0.55-0.87) than intermediate bedtime. In contrast, early bedtime was correlated with a higher risk of poor total power (OR = 1.23, 95% CI: 1.05-1.45) and high frequency power (OR = 1.18, 95% CI = 1.00-1.39). When further specifying sleep duration and physical disability into the regression models, the inverse association between late bedtime and unhealthy HRV remained; however, the association between early bedtime and HRV disappeared. Accordingly, we concluded that in terms of cardiac autonomic function, early bedtime in older adults is not necessarily beneficial for their health outcomes, whereas late bedtime may not be detrimental.Abbreviations: ADL: activity of daily living; BMI: body mass index; CI: confidence interval; GARS: the Groningen Activity Restriction Scale; HADS: The Hospital Anxiety and Depression Scale; HF: high frequency power; HRV: heart rate variability; LF: low frequency power; LF/HF: low frequency to high frequency ratio; OR: odds ratios; TP: total power.
Keywords: Bedtime; cardiac autonomic function; community-based study; sleep-wake pattern.