Extended waves of extreme heat and elevated levels of particulate matter, a dangerous pollutant, may combine to significantly raise the risk of a fatal heart attack, a study found.

Research published Monday in the American Heart Association’s flagship journal, Circulation, analyzed more than 202,000 heart attack deaths in China between 2015 and 2020 and discovered a strong connection between extreme temperatures, heavy pollution and deadly heart attacks, especially among women and older adults.

The findings bolster a growing body of research tying hazards worsened by human-induced greenhouse gas emissions to adverse health impacts.

“Extreme temperature events are becoming more frequent, longer and more intense, and their adverse health effects have drawn growing concern,” Dr. Yuewei Liu, a senior author of the study and an associate professor of epidemiology in the School of Public Health at Sun Yat-sen University in Guangzhou, China, said in a release. “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.”

To quantify the impact of high heat with and without heightened pollution levels, the researchers focused on Jiangsu province in China, which typically has distinct seasons and a wide range of temperatures and particulate matter presence.

Temperatures were assessed using heat index, which combines base temperatures and humidity, and levels of particulate matter, known as PM2.5, were considered high if they surpassed the threshold of 37.5 micrograms per cubic meter. Particulate matter can come from a range of sources, from factories and cars to construction sites and trucks.

Heart attack deaths were then compared on the same day of the week in the same month across the span of the study. If, for example, a death occurred on the second Monday of August in 2015, the second Monday in Augusts that followed would be used as a control.

Deaths were mostly among older adults, with 52% occurring in individuals older than the age of 80, according to the study.

However, the researchers found an escalating risk of heart attacks as temperatures remained high and pollutant levels lingered at dangerous measures.

There was an 18% higher risk of fatal heart attacks when heat indexes were at or above the 90th percentile, which, for the study, ranged between 82.6 degrees Fahrenheit and 97.9 degrees.

That threat ballooned to 74% higher when heat indexes ranged between 94.8 degrees and 109.4 degrees during four-day heat waves. More than 6,400 of the 202,678 deaths observed in the research happened when heat stood above this threshold for three or more days.

People were twice as likely to die during four-day heat waves when particulate pollution was above 37.5 micrograms per cubic meter, the researchers said.

While there was a slight increase of heart attack deaths during cold snaps — a 4% rise — particulate matter did not appear to interact with colder weather in the same way as hotter temperatures.

Overall, the researchers estimated up to 2.8% of heart attack deaths could be attributed to extreme temperatures meshing with particulate matter pollution.

“Our findings provide evidence that reducing exposure to both extreme temperatures and fine particulate pollution may be useful to prevent premature deaths from heart attack, especially for women and older adults,” said Liu.

Heat is the deadliest climate change impact and worsens pollution from ozone and particle pollution, which is about 1/20th the width of a human hair and can become embedded in the lungs.

A growing body of research has found PM2.5 disproportionately affects communities of color and low-income populations in the U.S., despite overall levels of the pollutant falling in recent years.

The study authors said individuals should avoid going outside when temperatures are high, and strategies like using fans and air conditioners during hot weather could lower the risk of negative health impacts.

“Using an air purifier in the house, wearing a mask outdoors, staying clear of busy highways when walking and choosing less-strenuous outdoor activities may also help to reduce exposure to air pollution on days with high levels of fine particulate pollution,” said Liu. “To improve public health, it is important to take fine particulate pollution into consideration when providing extreme temperature warnings to the public.”


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