Co-exposure to CO2 and heatwaves and the risk for diabetes: a multi-center spatial epidemiological study in China

Climate change, closely linked to the increasing CO 2 concentrations and heatwave events, may directly and indirectly affect the risk for diabetes, which has been a leading cause of disability worldwide. Using the baseline survey of a large multi-center cohort including 134,403 participants in China, this study for the first time examined the associations of CO 2 and heatwaves with the risks for diabetes/prediabetes at an individual level. The exposure to CO 2 and heatwaves was estimated at spatial resolutions of 10 km and 27 km, respectively. Multilevel logistic regression models with random intercepts at the community level were used to estimate the associations after adjusting for individual-level covariates. Subgroup and sensitivity analyses investigated the variations and robustness of the association, respectively, while mediation analysis estimated the mediation effect of body mass index (BMI) on the association. Elevated fasting blood glucose levels were associated with higher CO 2 concentrations ( β = 0.09 [95% CI: 0.07, 0.12]) and increased heatwave frequency ( β = 0.22 [95% CI: 0.09, 0.35]), both of which were also associated with the increased risks for diabetes (CO 2 : OR = 1.14 [1.09, 1.19]; heatwaves: OR = 1.48 [1.17, 1.89]). The association between CO 2 and diabetes was stronger among individuals with less than a high school education, those residing in rural areas, and those living in non-compact built environment. The association between heatwaves and diabetes was stronger among individuals consuming ≥ 400 g/day of fruit and vegetable. Among those who experienced heatwaves, BMI mediated about 8.2% and 2.9% of the associations between CO 2 and diabetes and prediabetes, respectively; among those who did not experience heatwaves, BMI mediated about 11.5% of the association between CO 2 and prediabetes. Higher CO 2 concentrations and increased heatwave frequency were associated with a higher risk of diabetes in China, with BMI partially mediating CO 2 -diabetes association among individuals who experienced heatwave events. This study would advance our understanding of the health effects of climate change and provide scientific evidence for climate change mitigation.