Association of coexposure to indoor solid fuels, outdoor air pollution, and heatwave with the risk of Cardiometabolic Multimorbidity among middle-aged and older Chinese adults.

BACKGROUND: Indoor solid fuels, outdoor air pollution (PM1, PM2.5, and PM10), and heatwave are all modifiable environmental factors. However, their mixed effects on Cardiometabolic Multimorbidity (CMM) and its core component diseases (diabetes, heart disease, and stroke) remain unclear. METHODS: In this study, four diseases analysis cohorts (CMM: n = 10,273; diabetes: n = 9,893; heart disease: n = 9,536; and stroke: n = 10,466) were constructed using data from the five waves (2011, 2013, 2015, 2018, and 2020) of the CHARLS. A time-varying Cox proportional hazards model was used to estimate the hazard ratio (HR) for environmental factor exposure. The Cumulative Risk Index (CRI) and the Quantile g-computation (Qgcomp) model were employed to assess the cumulative effect and component weights of coexposure to multiple environmental factors. RESULTS: The single-exposure analysis indicated that indoor solid fuels use significantly increased heart disease (HR = 1.118, 95% CI 1.016-1.231) and stroke (HR = 1.149, 95% CI 1.007-1.310) risks. PM1, PM2.5, and PM10 were the most consistent risk factors for CMM, diabetes, and heart disease (all HRs > 1, P < 0.001), and heatwave was sometimes associated with higher risks of CMM, diabetes, and heart disease. The CRI analysis demonstrated that coexposure to multiple environmental factors increased the CMM, diabetes, and heart disease risks. The Qgcomp model further showed that these coexposure increased the risk of four diseases, with ORs (95% CIs) (CMM:1.650, 1.375-1.979; diabetes: 1.675, 1.475-1.903; heart disease: 1.228, 1.080-1.397; stroke: 1.205, 1.011-1.437), with indoor solid fuels use as the primary contributor. CONCLUSIONS: In conclusion, long-term coexposure to indoor solid fuels, outdoor air pollution, and heatwave increased the risk of CMM and its core component diseases. Indoor solid fuels play a main role in these effects.