Associations of Sleep Quality with Gait Speed and Falls in Older Adults: The Mediating Effect of Muscle Strength and the Gender Difference.

Introduction Although previous studies have reported the significant associations of sleep quality with gait speed and falls, the mechanisms underlying these associations are unclear. We aimed to examine the gender-specific associations of sleep quality with gait speed and falls among older adults and to explore the possible mediating effect of muscle strength on these relationships. Methods Data were taken from wave 6 (2012-2013) of the English Longitudinal Study of Aging (ELSA), including 7,664 participants aged 60 years and older. Sleep quality and falls were assessed by self-report. Gait speed was measured by the "timed walking test" and then adjusted by height. As an indicator of overall muscle strength, grip strength was measured by using the Smedley dynamometer. Baron and Kenny's causal steps and the Karlson/Holm/Breen method were used to examine the mediating effect. Results Higher sleep quality was associated with the higher level of gait speed (β = 0.008, p = 0.031 in men; β = 0.008, p = 0.017 in women) and with lower prevalence of falls (OR = 0.878, 95% CI: 0.773, 0.998 in men; OR = 0.874, 95% CI: 0.792, 0.965 in women). Grip strength mediated these associations in men but not in women, and the mediating effects of grip strength can explain 23.74 and 11.01% of the total effect of sleep quality on gait speed and falls, respectively. Conclusion Our findings help explain the mechanism underlying the associations of sleep quality with gait speed and falls. Effort to maintain the mobility of the older men should focus on improving both sleep quality and muscle strength.