The relationship between BMI and ACS in-hospital mortality: findings from the Chinese Cardiovascular Association-Chest Pain Center Registry

Background Obesity is a global epidemic associated with major cardiovascular (CV) risk factors. While previous studies have suggested an "obesity paradox" in patients with acute coronary syndrome (ACS), characterized by a protective effect of higher body mass index (BMI), its consistency across different demographics and clinical subtypes remains debated. Purpose To evaluate the association between BMI and in-hospital mortality among Chinese ACS patients and to examine whether this relationship is modified by age, sex, and disease subtype. Methods This retrospective cohort study analyzed ACS patients from the Chinese Cardiovascular Association (CCA) Database – Chest Pain Center between January 2016 and December 2023. The primary outcome was in-hospital mortality. Logistic regression and Inverse Probability of Treatment Weighting (IPTW) were used to adjust for baseline confounders. Restricted cubic splines (RCS) were employed to model potential nonlinear associations, with results stratified by age, sex, and ACS subtype. Results The study included a total of 898,798 patients diagnosed with ACS, of whom 32,357 (3.6%) were underweight, 511,779 (56.9%) were normal weight, 299,709 (33.3%) were overweight, and 54,953 (6.1%) were obese. Patients with obesity or overweight exhibited a higher prevalence of classic CV risk factors, a greater proportion of males, higher rates of PCI, shorter pre-hospital delays, and were generally younger. Conversely, underweight patients had a higher burden of other comorbidities. A U-shaped relationship between BMI and in-hospital mortality was observed across the overall population and both sexes. Notably, among ACS patients under 45 years (premature coronary artery disease), the relationship demonstrated a near-linear increase in mortality with higher BMI. In contrast, the classic U-shaped curve remained evident in patients over 60 years. Conclusions A U-shaped association between BMI and in-hospital mortality exists in Chinese ACS patients, though this relationship transitions to a linear increase in younger cohorts. These findings suggest that body weight control strategies should be more precise and tailored to patient age to improve clinical outcomes.