Joint Exposure to Ozone and Temperature and Acute Myocardial Infarction Among Adults Aged 18 to 64 Years in the United States

BACKGROUND: Previous research suggests that exposures to air pollution and nonoptimal temperatures are associated with a higher risk of acute myocardial infarction (AMI), but few studies examined the exposures jointly. Furthermore, moderate exposures were often overlooked. We evaluated short-term exposure to ambient ozone pollution and ambient temperature jointly and over the entire range of exposures, with the occurrence of AMI among adults aged 18 to 64 years (an understudied population) in the contiguous United States. METHODS: We identified eligible individuals with incident AMI insured by a nationwide private insurance company from 2016 to 2020. We designed a time-stratified case-crossover study in which each patient's ambient exposure to ozone and temperature on the day of their AMI was compared with their exposures on a nearby day. We used a 2-stage model to investigate the associations with joint exposures: (1) fitting climate region-specific models with statistical interaction terms between ozone and temperature, and (2) using a multivariate random-effects meta-analysis to pool the region-specific estimates. RESULTS: We included 270 123 adults with incident AMI and observed a significant association between joint ozone-temperature exposures and increased AMI. Compared with the reference of ozone at 35 ppb and temperature at the first percentile, joint exposure to ozone at 60 ppb and temperature at the 95th percentile at lag 0 day was associated with a 33% (95% CI, 16%-51%) increase in incident AMI, and joint exposure to ozone at 50 ppb and temperature at the median was associated with a 15% (95% CI, 4%-28%) increase. There was heterogeneity by sex, with women showing increased odds when both ozone and temperature were high and men showing increased odds when either ozone or temperature was high. CONCLUSIONS: Joint exposure to ozone pollution and high temperature increased the probability of AMI among younger adults, even when one of the exposures was moderate. This study highlights the importance of addressing exposures to ozone and nonoptimal temperature simultaneously in AMI prevention strategies.