P23: Association of exercise with melatonin level in community- dwelling older adults

Abstract

Summary: Melatonin serves as an endogenous synchronizer of biological rhythms. Age-related changes are evident with a significant reduction in melatonin observed in 24-hour secretion. Melatonin exerts a significant cytoprotective action by buffering free radicals and reversing inflammation. However, few studies have explored the association between physical activity and melatonin level. In this study, we compared melatonin level and actigraphy-derived sleep and activity indicators in older adults across two levels of exercise habit (sedentary-to- light exercise and moderate -to-vigorous exercise), as well as the association of these indicators with melatonin levels. We recruited 104 participants (aged 57– 84 years) who wore a wristwatch device to monitor their activity (MotionWatch 8; CamNtech, Cambridge, UK) for 14 days. Circadian rhythms were estimated using cosinor analysis, lag 1440 mins correlation coefficient, interdaily stability, and non-parametric analysis. Saliva samples were collected every 30 mins from 18:00 pm till one hour before usual bedtime, and maximum melatonin level during this period. A 5-minute Psychomotor Vigilance Task (PVT) was used to evaluate attention. Habits of physical activities were self-reported. Melatonin level was not significantly different between participants with sedentary- to-light and moderate-to-vigorous exercise habits. Analysis showed that participants who had moderate-vigorous exercise habit were older (p = 0.04), having longer sports time (p < 0.001) and WASO (p = 0.02), more occurrence of daytime naps (intradaily variability) (p = 0.05), more fragmentated 24-h sleep-wake cycle (interdaily stability, p = 0.01), and less regular 24h rhythm (lag 1140 mins correlation, p = 0.04). They also showed shorter response time (p = 0.05), and a smaller number of lapses (p = 0.04) in PVT. Regression analysis results showed that weekly exercise time is positively associated with melatonin level. Additionally, a later start hour of M10 is associated with 5.95 pg/ml increase in melatonin level. In consistent, exercise in older adults did not promote a robust sleep- wake cycle but is related to better cognitive function and higher melatonin levels.