When people—especially women and older adults—are exposed to both extreme temperature events (ETEs) and ambient fine particulate matter (PM25), they are at greater risk for myocardial infarction (MI) mortality, according to new study results. Additionally, the study finds, fatal MIs can be triggered by heat waves synergistically interacting with PM25, but cold spells do not show the same interaction. These data were reported by Ruijun Xu, MD, and Suli Huang, MD, PhD, of Sun Yat-sen University, Guangzhou, China, and colleagues, in a manuscript published Monday online and in the July 25 issue of Circulation. Global climate change is predicted to drastically increase the number of ETEs worldwide, including more frequent and intense temperature extremes. ETE exposure is known to increase risk of cardiovascular events, especially MI0-related emergency department visits and hospitalizations. MI morbidity due to extreme temperatures has been studied broadly, but the literature is lacking on the influence of heat and cold spells on MI mortality alongside PM25 in causing MI deaths. The investigators of this time-stratified, case-crossover study examined 202,678 MI deaths (mean age=77.6±13.3 years, 48.0% female) over five years, from 2015 to 2020, in Jiangsu province, China. They investigated the interactive effects of patient exposure to ETEs and PM25 with MI mortality. ETE definitions—12 total—were created using various temperature thresholds and durations. Validated grid datasets were used to assess daily ETEs and exposures to PM25. Exposure-response analysis and estimation of relative excess odds were performed using conditional logistic regression models. Heat odds ratio of associated MI mortality 1.18 (95% confidence interval [CI]=1.14-1.21) to 1.74 (95% CI=1.66-1.83), and the range was 1.04 (95% CI=1.02-1.06) to 1.12 (95% CI=1.07-1.18) for cold spell association with MI mortality. Odds of MI mortality significantly increased at lag 01-day exposure (the day before) to PM25. There was also a significant synergistic interaction between heat waves and PM25 with MI mortality (relative excess odds due to interaction >0, proportion attributable to interaction >0, synergy index >1), and this interaction was stronger as heat waves intensified or lasted for longer periods of time. The investigators estimated that roughly 2.8% of the examined MI deaths were attributable to ETEs and PM25 exposure, when the levels exceeded the World Health Organization’s interim target 3 value (37.5 μg/m3) in the air quality guidelines. Older adults and women were more likely to experience negative effects from ETEs and PM25 exposure. Socioeconomic status, age and sex were not significantly influenced by the interactive effects of ETEs or PM25. Overall, women and older adults were more likely to experience MI mortality related to ETEs and PM25 interactions. Heat waves, cold spells and PM25 exposure significantly increase the chances of MI mortality, and longer durations of heat or cold, or more intense temperatures, also increase the risk of MI mortality. Explaining the more pronounced effect of ETE and PM25 interactions on older adults and women, the authors wrote that physiologically, women have less sweat capacity, less ability to self-regulate their body temperatures, and greater airway sensitivity to particulate matter as compared with men. Concerning older adults, the authors wrote that temperature regulation is known to break down with age and that other conditions that develop as people age can also decrease the body’s ability to thermoregulate and increase sensitivity to fine particulate matter. “Strategies for individuals to avoid negative health effects from extreme temperatures include following weather forecasts, staying inside when temperatures are extreme, using fans and air conditioners during hot weather, dressing appropriately for the weather, proper hydration and installing window blinds to reduce indoor temperatures,” said Yuewei Liu, MD, PhD, an associate professor at Sun Yat-sen University and the paper’s senior author, in an American Heart Association news release announcing the new study results. The authors of the study concluded that mitigating PM25 exposure will continue to be important, especially during heat waves. Physiological responses to extreme temperatures and pollution exposure can lead to a cascade of harmful side effects on the body. “Extreme temperature events are becoming more frequent, longer and more intense, and their adverse health effects have drawn growing concern. Another environmental issue worldwide is the presence of fine particulate matter in the air, which may interact synergistically with extreme temperatures to adversely affect cardiovascular health,” Liu said. Source: Xu R, Huang S, Shi C, et al. Extreme Temperature Events, Fine Particulate Matter, and Myocardial Infarction Mortality. Circulation. 2023;148:312-323. Image Credit: Günter Albers – stock.adoe.com