Association of joint exposure to PM2.5 and extreme heat with cardiovascular disease: A population-based cohort study in Northwest China

Extreme heat and fine particulate matter (PM 2.5 ) may increase cardiovascular disease (CVD) mortality, but their combined impact on overall CVD incidence is unclear. We aimed to evaluate their independent effects, identify vulnerable populations, and explore interactions, using a 2019 cohort of 5,070,689 adults. This year's average PM 2.5 and extreme heat (annual ratio of extreme heat days (AREHDs), annual ratio of extreme heat hours (AREHHs)) exposures were analyzed via accelerated failure time (AFT) models. Each 1 μg/m 3 PM 2.5 increase shortened CVD onset time by 0.083% (95% confidence interval [CI]: −0.009–0.175), most affecting the elderly, males, smokers, drinkers, and those with hypertension or diabetes. Each 1% of AREHD and AREHH increase reduced onset time by 0.446% (95% CI: 0.304–0.587) and 1.379% (95% CI: 1.043–1.714), stronger in the elderly, males, and sedentary individuals. PM 2.5 and extreme heat exerted synergistic detrimental effects, with the greatest risk observed at medium levels of co-exposure.