Associations Between Physical Activity Trajectories and Circadian Syndrome Among Middle-Aged and Older Adults in China

Objective: Circadian rhythm syndrome (CircS) is associated with multiple adverse health outcomes. Physical activity (PA) is a key modifiable behavior in middle-aged and older adults, yet evidence linking it to CircS remains limited. This study aimed to examine the relationship between physical activity trajectories and CircS. Methods: Using data from the China Health and Retirement Longitudinal Study (CHARLS), 2011–2015, PA was assessed using the IPAQ, and trajectories were identified using Group-Based Trajectory Model (GBTM). Logistic regression models examined associations between PA trajectories and CircS, with stratified analyses performed. Associations between PA levels and CircS were further examined using 2015 data. Restricted cubic spline (RCS) models assessed dose–response relationships, with sensitivity and subgroup analyses conducted. Results: Among 1,488 participants, four PA trajectories were identified: Stable low (12.4%), Stable middle (40.0%), Stable high (40.7%), and Initial decline–subsequent increase (6.9%).. Using the Stable Low trajectory as reference in logistic regression, after adjusting for all covariates, the Stable Middle, Stable High, and Initial Decrease-Subsequent Increase trajectories were significantly associated with reduced risk of CircS: (OR = 0.40, 95% CI: 0.27–0.57), and (OR = 0.46, 95% CI: 0.27–0.77), respectively. Subgroup analysis indicated that, with the low-to-moderate activity group as the reference, the high-activity group demonstrated consistent protective associations across all subgroups. After controlling for relevant covariates, engaging in vigorous physical activity (VPA), moderate physical activity (MPA), or light physical activity (LPA) at least 3 days per week, as well as at least 10–29 minutes of VPA/MPA or ≥30 minutes of LPA daily, were associated with a lower risk of CircS. The adjusted OR (95% CI) ranged from 0.38 (0.14, 0.93) to 0.74 (0.56, 0.97). RCS curves demonstrated a linear dose-response relationship between total physical activity (TPA) and CircS risk, consistent across populations. Conclusions: This study identified four PA trajectories and found that Initial decline-subsequent increase ，Stable-high and Stable middle trajectories, as well as higher PA levels, were associated with lower CircS incidence risk among middle-aged and older adults in China. Public health strategies should incorporate PA into primary CircS prevention for middle-aged and older adults.