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Extreme temperatures combined with high levels of air pollution dramatically increase the risk of older adults having a fatal heart attack, new research from China suggests.

The study, published this week in the ÃÛÑ¿´«Ã½ journal , found the risk of dying from a heart attack may double on days with both extremely high temperatures and excessive levels of pollution from fine particulate matter. Extreme cold also may raise fatal heart attack risks, the results showed.

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

Fine particulate matter in the air may "interact synergistically" with extreme temperatures to adversely affect cardiovascular health, Liu said. "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."

Fine particulate matter pollution comes from burning fuels and includes vehicle exhaust, factory emissions and wildfire smoke. Particles less than 2.5 microns can be easily inhaled deep into the lungs, where they can cause irritation to the lungs and blood vessels around the heart. Prior research has linked exposure to fine particulate matter pollution to heart disease, stroke and other health issues.

The researchers analyzed data for 202,678 heart attack deaths from 2015 to 2020 in Jiangsu province, a coastal region in eastern China with a wide range of temperatures and fine particulate matter levels. The people who died were nearly 78 years old on average.

Fine particulate matter pollution levels were measured on the day of and day before each death. Particulate matter levels were considered high on any day the average exceeded 37.5 micrograms per cubic meter.

Extreme temperatures were measured using the daily heat index, which reflects the combined impact of heat and humidity. A heat wave was defined as temperatures at or above 82.6 degrees Fahrenheit for two or more days. The days a heart attack death occurred were compared with control days defined as the same day of the week within the same month. That is, if a heart attack occurred on a Wednesday, every other Wednesday in the same month would be considered a control day.

Compared to control days, researchers found the risk of a fatal heart attack was twice as high during four-day heat waves with fine particulate pollution above 37.5 micrograms per cubic meter. It was 18% higher during two-day heat waves when temperatures ranged from 82.6 to 97.9 degrees Fahrenheit, and 74% higher during four-day heat waves when heat indexes reached 94.8 to 109.4 degrees Fahrenheit.

Extreme cold also affected the risk of having a fatal heart attack. Compared to control days, the risks were 4% higher during two-day cold snaps when temperatures ranged from 33.3 to 40.5 degrees, and 12% higher during three-day cold snaps when temperatures were 27 to 37.2 degrees. But unlike with extreme heat, there was no added risk of a fatal heart attack when extreme cold was combined with pollution exposure.

During heat waves, cold snaps and days with high levels of pollution, the risk of heart attack death was generally higher among women than men, and among adults 80 and older compared to younger adults.

The researchers estimated that up to 2.8% of fatal heart attacks in the study could be attributable to the combination of extreme temperatures and elevated levels of fine particulate pollution.

To prevent negative effects on health, Liu recommended monitoring weather forecasts and staying inside when temperatures reach extremes, using fans and air conditioners to cool down, dressing appropriately for the weather, staying hydrated and installing window blinds to reduce indoor temperatures.

Liu also said the added risk associated with high levels of pollution can be avoided by using an indoor air purifier, wearing a mask outdoors, staying clear of busy highways when walking and choosing less strenuous outdoor activities.

"To improve public health, it is important to take fine particulate pollution into consideration when providing extreme temperature warnings to the public," Liu said.