Dual exposure to extreme temperatures, air pollution raises risk for mortality
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Exposure to both extreme heat and air pollution were linked to an increased risk for all-cause mortality, according to a study published in American Journal of Respiratory and Critical Care Medicine.
“Understanding the risks associated with these exposures is really important, because we know that they will increase with climate change in many different parts of the United States and the world,” Erika Garcia, PhD, MPH, senior author of the study and assistant professor of population and public health sciences at the Keck School of Medicine of USC, said in a press release.
In a time-stratified case-crossover study using conditional logistic regression, Garcia and colleagues analyzed more than 1.5 million individuals (mean age, 74 years; 51.6% male) who died in California between Jan. 1, 2014, and Dec. 21, 2019, to determine if exposure to both extreme temperatures and fine particulate matter (PM2.5) is linked to all-cause, cardiovascular and respiratory death.
Researchers calculated each individual’s daily average PM2.5, based on their address, as well as the maximum and minimum temperatures of their date of death. They then categorized each recorded day according to one of four levels of exposure: no extreme exposure to either variable, extreme heat exposure only, extreme air pollution exposure only or both extreme heat and air pollution exposure.
Researchers compared these days with 5.1 million control days, which they classified as the same weekdays from the same month and year as the date of death.
When evaluating individual risks for all-cause mortality against control days, researchers found a 6.1% (95% CI, 4.1%-8.1%) increased risk on maximum temperature days and a 5% (95% CI, 3%-8%) increased risk on extreme PM2.5 days. However, once exposure to extreme maximum heat and air pollution were combined, risk for all-cause mortality increased to 21% (95% CI, 6.6%-37.3%).
This increased all-cause mortality risk persisted on days with the most extreme minimum temperatures alone (8.7%; 95% CI, 6.6%-10.8%) and in combination with PM2.5 (23.9%; 95% CI, 11.6%-37.5%) compared with control days.
For cardiovascular mortality, researchers studied 492,513 deaths (mean age, 79 years; 51.4% male) and 1.7 million control days, showing a 29.9% (95% CI, 3.3%-63.3%) increased risk for cardiovascular death when exposures reached extreme maximum heat and extreme PM2.5 and a 33.3% (95% CI, 10.5%-60.7%) increased risk on days with extreme minimum temperatures and extreme PM2.5.
Researchers also analyzed 139,116 respiratory deaths (mean age, 78.8 years; 51% female) and 472,234 control days. The risk for respiratory death also increased on extreme coexposure days with maximum temperatures (38%; 95% CI, –12.5% to 117.7%) and minimum temperature (44.4%; 95% CI, –0.4% to 109.4%).
Additionally, when stratified for age, researchers found that those aged older than 75 years were more likely to face a greater mortality risk.
“Assessment of the health impacts of combined exposure to extreme air pollution and heat events is urgent, given projected increases in the frequency of heatwaves and high pollution days with the progression of climate change,” Garcia and colleagues wrote. “These extremes will likely increasingly co-occur as a result of the shared underlying effects of climate change, so the cumulative burden of climate change-driven extreme air pollution and temperature cannot be estimated from the extreme of each acting alone but from their co-occurrences.”
With the threat of climate change, protective measures and interventions should be put in place, Garcia said in the release.
“If certain communities face an increased risk when these exposures occur, that will highlight an important target for interventions,” Garcia said.
This study by Garcia and colleagues adds to the literature indicating that more research is needed on how extreme temperature and air pollution exposure together impact an individual’s health, according to an accompanying editorial by Patrick L. Kinney, ScD, professor of environmental health in the Boston University School of Public Health, and Kent E. Pinkerton, PhD, professor of pediatrics in the School of Medicine and professor of anatomy, physiology and cell biology in the UC Davis School of Veterinary Medicine.
“With accelerating climate change and the emergence of wildfires as a significant source of high air pollution episodes, it will be increasingly important to understand and mitigate the human health effects of exposure to degrees of air pollution and temperature,” Kinney and Pinkerton wrote. “Future research should explore further whether, how, and to what extent wildfire PM2.5 has a distinct toxicity profile as compared with non-wildfire PM2.5 and how those factors are influenced by temperature.
“More information will also be needed on effective measures to protect individuals from exposure to extreme climate events, including building air cleaning and conditioning systems,” Kinney and Pinkerton added. “The urgency for further research on these topics will continue to intensify together with further changes in our climate.”
References:
Kinney PL, et al. Am J Respir Crit Care Med. 2022;doi:10.1164/rccm.202207-1372ED.
Risk of death surges when extreme heat and pollution coincide. https://keck.usc.edu/risk-of-death-surges-when-extreme-heat-and-air-pollution-coincide/. Published June 29, 2022. Accessed Nov. 28, 2022.