Independent and joint associations of circadian syndrome and estimated body fat mass with incident heart disease in older Chinese adults

Although the individual associations of circadian syndrome (CircS) and estimated body fat mass (BFM) with heart disease (HD) have been documented, their joint impact remains poorly understood. This study aimed to investigate the independent and joint associations of CircS and estimated BFM with self-reported incident HD. This study analyzed longitudinal data from the China Health and Retirement Longitudinal Study (CHARLS), collected between 2011 and 2020, which included 2,030 participants aged ≥ 60 years. CircS was defined as the presence of at least four out of its seven components. BFM was estimated using sex-specific equations that incorporated body mass index (BMI) and age, and this metric conceptually reflects adiposity. We used Cox proportional hazards regression models to examine the associations of CircS and estimated BFM with self-reported incident HD. Kaplan–Meier survival curves were generated for the CircS–BFM joint groups and were compared by the log-rank test (with statistical significance set at P < 0.05). Additionally, subgroup analyses and time-dependent receiver operating characteristic (ROC) curve analyses were performed. In the fully adjusted model, both CircS (hazard ratio [HR] = 1.27, 95% confidence interval [CI]: 1.01–1.60) and estimated BFM (HR = 1.47, 95% CI: 1.06–2.05) were independently associated with self-reported incident HD. In the joint analysis, participants who had both CircS and BFM levels at or above the sample median were associated with a higher risk of self-reported incident HD (HR = 1.67, 95% CI: 1.15–2.43). Kaplan–Meier analysis further demonstrated that the group with both risk factors had a significantly higher cumulative self-reported incidence of HD than the other groups (log-rank P < 0.05). However, the combined CircS–BFM assessment showed poor discriminative ability, with only a marginal numerical increase over CircS or BFM alone. Subgroup analyses identified significant interactions of sex and smoking status with the association between CircS and self-reported incident HD, as well as of residence with the association between estimated BFM and self-reported incident HD. However, these interactions did not remain statistically significant after Bonferroni correction. Among older Chinese adults, CircS and estimated BFM were independently and jointly associated with self-reported incident HD. However, the joint model demonstrated relatively poor predictive performance and, therefore, cannot currently be recommended as a standalone clinical prediction tool. Further validation in larger and more diverse populations is warranted.