Sulfur dioxide exposure is associated with kidney dysfunction and creatinine abnormalities in Chinese patients with cardiovascular disease or hypertension

This observational study examined the association between long-term ambient air pollution exposure and renal dysfunction among middle-aged and elderly Chinese individuals with hypertension or heart disease. Although previous studies have mainly focused on particulate matter and nitrogen dioxide, the epidemiological relevance of SO₂-related exposure patterns to creatinine abnormality and clinically identified cardiovascular disease or hypertension complicated by kidney dysfunction in cardiovascular populations remains insufficiently clarified. A total of 10,048 participants aged ≥ 45 years from the China Health and Retirement Longitudinal Study (CHARLS) were included. Long-term exposure was estimated using residentially matched annual average Air Quality Index (AQI) and seven major air pollutants from 2015 to 2020. Abnormal creatinine was defined according to age- and sex-specific serum creatinine reference ranges, and cardiovascular disease or hypertension complicated by kidney dysfunction was operationally defined as cardiovascular disease complicated by clinically identified renal disease in the CHARLS setting. Multivariable logistic regression, restricted cubic spline analysis, and six machine-learning models with SHAP interpretation were applied. AQI exposure was positively associated with abnormal creatinine and clinically identified cardiovascular disease or hypertension complicated by kidney dysfunction. In the fully adjusted model, each 1-unit increase in AQI was associated with higher odds of abnormal creatinine (OR = 1.0129, 95% CI: 1.0102–1.0157, P < 0.0001) and cardiovascular disease or hypertension complicated by kidney dysfunction (OR = 1.0084, 95% CI: 1.0055–1.0113, P < 0.0001). Restricted cubic spline analysis suggested a non-linear exposure–response relationship, with increased odds particularly when AQI exceeded approximately 80. XGBoost and LightGBM showed the best discrimination for abnormal creatinine and cardiovascular disease or hypertension complicated by kidney dysfunction, respectively. SHAP analysis suggested that SO₂ was an important contributor to model prediction; however, this finding reflects predictive importance rather than causal evidence. Long-term air pollution exposure, particularly SO₂-related exposure patterns, was associated with renal dysfunction among Chinese patients with cardiovascular disease. These findings support the need for environmental risk assessment in cardiorenal prevention, while further longitudinal studies with repeated renal measurements, albuminuria, eGFR, personal exposure assessment, and mechanistic biomarkers are needed to validate causality and biological pathways.