Heart Attack Risk Rises Significantly on Extremely Hot, Polluted Days

Extreme heat and air pollution can be dangerous for the heart. Enduring both at the same time can be especially deadly, new research shows.


The risk of having a fatal heart attack doubles during heat waves that last several days and overlap with periods of poor air quality, according to an analysis of heart attack deaths published Monday in the journal Circulation.


“The two things together are more than a double whammy,” said Dr. Joel Kaufman, an epidemiologist at the University of Washington who wasn’t involved in the study.


On their own, higher-than-normal temperatures or air pollution increased the risk of deadly heart attacks, showed the analysis of more than 200,000 heart attack fatalities between 2015 and 2020 in the Chinese province of Jiangsu. But when both occurred simultaneously, they were found to amplify each other’s effects, the study found.

Extreme heat has stifled parts of North America, Europe, Asia and Africa this summer, with blistering temperatures setting records worldwide. Meanwhile, poor air quality has also hit swaths of the U.S. due to forest fires originating in Canada. In the past week, wildfires have forced people to flee their homes in states including Washington, Oregon and Arizona.


When temperatures are extreme, the heart has to work harder and air pollutants put additional stress on the heart and other organs, Kaufman said. These stressors could trigger a heart attack in someone already at risk of having one, he said.


High temperatures and polluted air have been linked in studies to both short-term and chronic health problems, including heart and kidney disease, and cognitive issues. Older people, smokers and people with heart disease, high blood pressure, diabetes or other underlying health conditions are especially vulnerable to these stressors.


“Days with both extreme temperatures and air pollution are special times of concern when people, especially those at risk, are going to need to curb their activities,” Kaufman said.

A meta-analysis published last year in the Lancet Planetary Health found that heat waves increased the risk of heart-disease-related death by about 12%. Prolonged exposure to air pollution can contribute to a more rapid buildup of plaque in the heart’s arteries, a 2016 analysis published in The Lancet showed.


For the recent analysis, researchers in China and the U.S. used a statistical technique to uncover possible links between the incidence of fatal heart attacks in Jiangsu and hotter- or colder-than-average temperatures, as well as poor air quality. Air quality was considered poor when concentrations of fine particulate matter, a type of pollutant, exceeded a 24-hour average of 37.5 micrograms per cubic meter of air. Fine particulate matter, also known as PM2.5, is defined as particles that are 2.5 micrometers or less in diameter. They are so tiny they can penetrate deeply into the lungs and be absorbed into the blood.


Fossil fuel emissions from industrial facilities, power plants and cars, as well as wildfires, are significant sources of PM2.5 pollution.

World Health Organization air-quality guidelines state that 24-hour average concentrations of PM2.5 shouldn’t exceed 15 micrograms per cubic meter of air. But the WHO has set 37.5 micrograms as an interim target for highly polluted areas.

Risk of a deadly heart attack increased the higher the heat and the more prolonged it was, the study found. Two consecutive days of temperatures at around 100 degrees Fahrenheit increased the risk of fatal heart attack by 30%, researchers said. Four days in a row of similar heat increased the risk by 50%.


Exposure to high levels of PM2.5 on its own was associated with a 2% increased risk of deadly heart attacks, the study said. When high-heat days coincided with poor air quality, the risk shot up significantly. Two days in a row of 100-degree heat, plus polluted air, was associated with an 84% increased risk. Four consecutive days of similar heat and pollution doubled the risk, the paper showed.


Very cold temperatures also enhanced the risk of fatal heart attacks, the analysis said, though slightly less than very warm days.


“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,” said Dr. Yuewei Liu, an epidemiologist at Sun Yat-sen University in Guangzhou, China, and a study co-author.

People who are elderly, suffer from heart disease or are otherwise more vulnerable should take steps to protect themselves during hot and polluted days, said Dr. Andrea Baccarelli, chair of Columbia University’s environmental health sciences department, who wasn’t involved in the study.

“If a heart already doesn’t have good blood supply, it can be a perfect storm,” he said.


Public-health experts recommend staying indoors and using air-conditioning, as well as an air purifier, during very hot and polluted days. To beat the heat, people should plan outdoor activities during the cooler hours of the morning or evening, and should stay hydrated, experts said. They also recommend that people regularly check air-quality monitoring websites like AirNow.gov, and should limit outdoor activities and wear a well-fitted N95, or better, mask if air quality is poor.

Heart Attack Risk Rises Significantly on Extremely Hot, Polluted Days - WSJ