Exposure to both ozone pollution and higher ambient temperature, even when one exposure is moderate, increases the probability of an acute myocardial infarction (AMI) in younger adults, according to a large U.S. study published June 3 in Circulation.

In this time-stratified case-crossover study, Lingzhi Chu, PhD, Harlan M. Krumholz, MD, SM, FACC, et al., identified 270,123 adults (30% women) aged 18-64 years with incident AMI who were insured with a private nationwide company from 2016 to 2020. They compared each patient's local ozone concentration and temperature on the day of their AMI event with exposures on a nearby day.

Joint exposure to ozone at 35 parts per billion (ppb) and temperature at the first percentile was considered the reference. Results showed that joint exposure to ozone at 60 ppb and temperature at the 95th percentile (considered extreme exposures) at lag 0 day was associated with a 33% increase in AMI events vs. the reference. Moreover, joint exposure to ozone at 50 ppb and temperature at the median (considered moderate exposures) was associated with a 15% increase in AMI.

In other findings, exposure-response patterns differed between sexes, whereby men were more vulnerable when exposure to either ozone or heat was relatively mild. Overall, most (70%) AMI events occurred in men. Regarding AMI subtype, 56% were NSTEMI and 35% were STEMI. Notably, the younger age group (aged 18-54 years) accounted for 44% of AMI events vs. 56% for those aged 55-64 years.

Chu and colleagues write the study findings are a "call for health policies and strategies to reduce joint exposure to ozone and heat, not only extreme exposures, but also exposures at the moderate levels." Once in place, this would help to reduce "the morbidity and mortality burden of AMI among younger adults" in particular.