Associations of Solid Fuel Use and Circadian Rhythm Syndrome With Physical Function and Muscle Strength in Middle-Aged and Older Adults: Nationwide Cohort Study in China.

Abstract

Background: The relationships among circadian rhythm syndrome, physical function, and muscle strength remain unclear.

Objective: This study aimed to demonstrate the separate and combined deleterious effects of solid fuel use and circadian rhythm syndrome on physical function and muscle strength.

Methods: We used data from the China Health and Retirement Longitudinal Study cohort. The study population consisted of participants who underwent comprehensive assessments of metabolism, circadian rhythm, indoor air pollution, physical function, and muscle strength at the initial evaluation. Muscle strength was assessed using repeated grip strength measurements, and physical function was assessed using a composite score of muscle strength, physical performance, and balance. Circadian rhythm syndrome was derived from the 5 diagnostic components of metabolic syndrome combined with sleep duration and depression. Logistic regression and linear mixed models were used to assess the relationships among solid fuel use, circadian rhythm syndrome, physical function, and muscle strength. Furthermore, we analyzed the mediating role of circadian rhythm syndrome and its combined effect with solid fuel use on physical function and muscle strength.

Results: A total of 7934 participants were included in the study, most of whom used solid fuels. Solid fuel use was positively associated with circadian rhythm syndrome (odds ratio [OR] 1.078, 95% CI 1.031-1.125; P<.05). Circadian rhythm syndrome was found to be a significant risk factor for impairment of physical function (β=-0.475; P<.05) and muscle strength (β=-0.304; P<.05). Participants who used solid fuels and had circadian rhythm syndrome needed to pay more attention to changes in physical function (β=-0.698; P<.05) and muscle strength (β=-0.332; P<.05). A significant interaction was observed between solid fuel use and circadian rhythm syndrome on physical function (P_interaction=.03) and muscle strength (P_interaction=.02). Circadian rhythm syndrome partially mediated the association between solid fuel use and physical function, accounting for 2.51% of the total effect.

Conclusions: Circadian rhythm syndrome exacerbates the adverse effects of solid fuel use on physical function and muscle strength. Fuel cleanliness and regular work and rest habits are crucial for the health of middle-aged and older adults.