Association Between Wrist-Worn Device-Estimated Sleep Efficiency and Hand Grip Strength in Older Outpatients With Cardiometabolic Diseases: Cross-Sectional Study.

BACKGROUND: Older outpatients with chronic diseases are susceptible to muscle weakness and functional disabilities. Recently, various wearable devices have been developed to generate health lifelogs in daily life; however, data from patients with chronic diseases remain scarce. Previous studies have shown that subjective sleep efficiency assessed by self-questionnaires is associated with grip strength, but whether objective sleep efficiency detected by wearable devices is associated with physical function and body composition remains unclear.

OBJECTIVE: The aim of this study is to clarify the association between sleep duration, sleep efficiency estimated by wearable watch, grip strength, frailty, and sarcopenia in outpatients with predominantly cardiometabolic diseases and the influence of diabetes as part of the Smart Watch Innovation for Geriatrics and Gerontology (SWING-Japan) project.

METHODS: In this cross-sectional study, the wrist-worn device Silmee 22 was used in an outpatient clinic of an acute care facility for 7-90 nights for the analyses, and individual average sleep duration and efficiency (wearable-estimated sleep efficiency: total sleep duration/time spent in bed) were calculated. Low grip strength was defined as <28 kg for men and <18 kg for women. Sarcopenia was defined based on the Asian criteria and frailty based on the Japanese version of Cardiovascular Health Study and Kihon Checklist criteria. Sleep indices were compared between individuals with and without these conditions. Next, logistic regression analysis was performed, with lower grip strength as the dependent variable and wearable-estimated sleep efficiency as the independent variable, adjusted for age, sex, BMI, glycohemoglobin, cognitive function (Mini-Mental State Examination), Geriatric Depression Scale-15 score, and daily step count measured using the ankle-worn device WalkX. Subgroup analyses were performed and stratified according to the status of diabetes mellitus.

RESULTS: Data from 165 patients (median age: 77 y; duration of device use: 65 d; diabetes prevalence: 55%) were used for analyses. Wearable-estimated sleep efficiency and sleep duration were significantly lower in patients with low grip strength than in those without (58.0% vs 62.7%, P=.006, 245 vs 276 min, P=.04). Wearable-estimated sleep efficiency was not associated with frailty, low muscle mass, or slow walking speed. After adjusting for the above variables, low wearable-estimated sleep efficiency, but not low sleep duration, was associated with a risk of lower grip strength (odds ratio 1.04, 95% CI 1.01-1.08; P=.02) by 1 percentage point decrease in wearable-estimated sleep efficiency. This association was observed in patients with diabetes (odds ratio 1.05, 95% CI 1.002-1.093; P=.04). However, no significant interaction was observed.

CONCLUSIONS: In older patients with cardiometabolic diseases, objective low wearable-estimated sleep efficiency evaluated with wrist-worn wearable devices was associated with low muscle strength. No evidence was found to suggest that the strength of this association differed according to diabetes status. Longitudinal studies are needed to clarify the long-term association between low wearable-estimated sleep efficiency and muscle strength in this population.