Association between relative muscle strength and circadian syndrome among middle-aged and older Chinese adults

Circadian syndrome (CircS), an expanded construct beyond metabolic syndrome incorporating circadian disruption markers, represents an emerging cardiometabolic health concern. The relationship between relative muscle strength (RMS) and CircS remains unclear. This cohort study utilized data from the China Health and Retirement Longitudinal Study (CHARLS). Cross-sectional analysis included 9421 participants aged ≥ 45 years from the 2011 survey. Longitudinal analysis included 3135 participants without CircS at baseline who were followed up through 2015. RMS was calculated as the ratio of handgrip strength to appendicular skeletal muscle mass. Multivariate logistic regression and Cox regression models, combined with restricted cubic spline (RCS) curves, were conducted to assess the correlation between RMS and CircS incidence. Among 9421 participants, 48.2% had prevalent CircS. In the fully adjusted model, each unit increase in RMS was associated with 17.9% lower odds of prevalent CircS (OR = 0.821; 95% CI 0.731-0.920). During follow-up, 722 incident CircS cases occurred. Participants in the highest RMS quartile had 26% lower risk of developing CircS compared with those in the lowest quartile (HR = 0.74; 95% CI 0.593-0.923). RCS analyses revealed an inverse association between RMS and CircS, with no significant evidence of nonlinearity detected.Higher RMS was associated with lower prevalence and incidence of CircS among Chinese middle-aged and older Chinese adults. Generalizability to other populations requires confirmation. Maintaining muscle quality may represent a modifiable target for preventing circadian and metabolic dysregulation.