The temporal relationship between long sleep duration and poor hand grip strength in older adults: The Yilan study.

Objectives: Muscle strength is an important subdomain of intrinsic capacity in older adults. Although poor muscle strength is closely correlated with long sleep duration, a causal relationship has not yet been established. This study aimed to examine whether long sleep duration predicted a decrease in hand grip strength or vice versa.

Methods: In this follow-up study involving a community-based fixed cohort, participants included community-dwelling older adults aged ≥65years residing in Yilan City, Taiwan. Self-reported sleep duration at night was categorized as short (<6 hours), mid-range (6 to <8 hours), and long (≥8hours). Hand grip strength was measured using a dynamometer, and poor hand grip strength was defined by age- and sex-specific cutoffs based on one standard deviation below the age- and sex-specific means of the data. Two temporal directions of analyses were performed between sleep duration and hand grip strength. First, baseline participants with good hand grip strength were followed-up to examine whether baseline long sleep predicted poor hand grip strength. In contrast, baseline mid-range sleepers were followed-up to examine whether baseline poor hand grip strength predicted long sleep.

Results: A total of 539 individuals, with an average age of 74.5±5.5years, participated in the study. The average follow-up period was 5.8±1.8years. Regarding factors predicting a decrease in hand grip strength, after controlling for various confounders, long sleep duration at baseline predicted incident poor hand grip strength at follow-up visits (odds ratio, 2.63; 95% confidence interval, 1.27-5.43). Conversely, poor hand grip strength failed to predict lengthening of sleep duration.

Conclusion: In older adults, long sleep duration preceded a decrease in hand grip strength.