A body shape index modifies the association between air pollution and cardiometabolic multimorbidity

Long-term exposure to air pollution is associated with cardiometabolic diseases, but the modifying role of body shape distribution on cardiometabolic multimorbidity (CMM) remains unknown. This study investigated whether A Body Shape Index (ABSI), a measure of abdominal adiposity, modifies the relationship between air pollution and CMM in Chinese middle-aged and older adults. We included 11,838 participants aged ≥ 45 years from the China Health and Retirement Longitudinal Study (CHARLS) Wave 3 (2015). CMM was defined as the coexistence of ≥ 2 cardiometabolic diseases (diabetes, heart disease, and stroke). ABSI was calculated as waist circumference/(BMI^(2/3) × height^(1/2)). Individual exposure to air pollutants-including particulate matter with an aerodynamic diameter ≤ 2.5 μm (PM₂.₅), ≤ 10 μm (PM₁₀), and ≤ 1 μm (PM₁); sulfur dioxide (SO₂); nitrogen dioxide (NO₂); and ozone (O₃)-was assessed using satellite-based spatiotemporal models. Generalized linear models examined associations between air pollution and CMM, with interaction terms to evaluate ABSI's modification effects. The final analysis included 10,487 participants, with 6,896 (65.8%) having cardiometabolic multimorbidity (CMM). All six air pollutants (PM2.5, PM10, SO2, NO2, O3, PM1) showed significant positive associations with CMM prevalence. In fully adjusted models, the odds ratios per interquartile range (IQR) increase ranged from 1.104 (95% CI 1.041-1.173) for O3 to 1.298 (95% CI 1.204-1.401) for PM1. ABSI was independently associated with increased CMM risk, with each IQR (0.005) increase associated with 14.2% higher odds (OR = 1.142, 95% CI 1.085-1.201). Significant interaction effects were observed between ABSI and all six examined air pollutants (P-interaction < 0.10). Stratified analyses revealed substantially stronger associations between air pollution and CMM among participants in the highest ABSI tertile compared to the lowest tertile. For example, PM1 showed an OR of 1.428 (95% CI 1.285-1.587) in the highest ABSI group versus weaker associations in lower ABSI groups. All sensitivity analyses confirmed the robustness of these findings. This study provides the first evidence that A Body Shape Index significantly modifies the association between long-term air pollution exposure and cardiometabolic multimorbidity in Chinese middle-aged and older adults. Individuals with higher ABSI values, indicating greater abdominal adiposity, experienced substantially stronger associations between air pollutant exposure and CMM risk. These findings suggest that central body fat distribution creates a metabolically vulnerable phenotype that amplifies environmental health risks. The results highlight the importance of considering body shape distribution when assessing air pollution health impacts and support targeted prevention strategies for high-risk individuals with central obesity in polluted environments. The demonstrated interaction between environmental and metabolic factors underscores the need for integrated approaches to cardiometabolic disease prevention that address both air quality improvement and obesity management.