• Posted July 25, 2023

Hot, Polluted Days May Double Heart Attack Risk

The extreme heat and choking wildfire smoke blanketing wide swaths of the United States this summer are actively dangerous to heart health, a new study reports.

Days where soaring heat combines with fine particulate air pollution can double a person's risk of a fatal heart attack, researchers have found.

“Heat wave exposure interacts synergistically with fine particulate pollution to trigger more heart attack deaths,” said senior researcher Yuewei Liu, an associate professor of epidemiology at Sun Yat-sen University's School of Public Health in Guangzhou, China.

These results show the direct danger to human health posed by climate change, said Dr. Sanjay Rajagopalan, chief of cardiovascular medicine at University Hospitals Harrington Heart and Vascular Institute in Cleveland.

“The interaction of these two factors -- wildfire smoke and high temperatures -- when you have both these things happening together, it elevates the risk for heart attacks even further,” said Rajagopalan, who was not involved in the study. “With climate change, this is becoming an everyday reality.”

For the new study, researchers analyzed more than 202,000 heart attack deaths that occurred between 2015 and 2020 in the Chinese province of Jiangsu.

They also gathered local heat index and air pollution measurements for both the day of and the day before each heart attack, to assess the increased risk posed by the combination of heat and smog. Heat index takes into account both temperature and humidity.

It's not news that air pollution increases heart attack risk, Rajagopalan said.

“The association between air pollution and heart attacks has been shown over and over again," he said. "This is a well-known risk.”

Fine particulates are less than 2.5 microns in size -- about 30 times smaller than the diameter of an average human hair strand, according to the U.S. Environmental Protection Agency.

When inhaled deep into the lungs, this particle pollution can irritate the lungs and the blood vessels around the heart, researchers said in background notes.

But researchers have only recently started to grasp how heat might harm heart health, and how it might combine with air pollution to raise risks even higher, Rajagopalan said.

“The linkages between how temperature and air pollution can interact together to amplify the risk for individuals are becoming much clearer,” he said.

Liu and his colleagues discovered that heat on its own is a heart hazard:

• Two-day heat waves with a heat index between 82 and 98 degrees Fahrenheit increased the risk of a fatal heart attack by 18%.
• Four-day heat waves of 95 to 109 degrees F increased heart attack death risk by 74%.

But that was just considering extreme heat.

The risk of dying from a heart attack actually doubled on days with both extreme heat and unhealthy air quality. These days posed the greatest increase in risk of all weather conditions studied.

The researchers also looked into the risk posed by cold snaps.

While extreme cold could increase the risk of heart attack death by 4% to 12%, it didn't combine with air pollution to significantly amplify risk further, they found.

Previous studies have shown that either high heat or air pollution can increase inflammation and stress in the body, Liu said.

In addition, high temperatures can actually increase a person's intake of air pollutants, by elevating blood flow and altering breathing patterns, he said.

Women were more likely than men to have a fatal heart attack on days of extreme heat, and seniors 80 and older were at higher risk than younger adults, the results showed.

However, everyone is at some level of risk when high heat and air pollution combine. The interactive effects of extreme heat and smog did not vary across gender, age or economic status, researchers concluded.

Rajagopalan said people should start paying frequent attention to air pollution levels reported on weather sites. On days where air quality takes a nose dive, they should stay indoors and use either an HVAC system with good filters or a portable air cleaner to keep the air fresh.

Those who must venture outside should use an N95 filter mask to protect themselves from airborne particles, he added.

People also can beat the heat by using fans and air conditioners, dressing appropriately, staying hydrated, and installing window blinds to reduce indoor temperatures, Liu said.

Rajagopalan said certain groups should be especially cautious: people with diabetes, children with respiratory conditions, people with COPD, organ transplant recipients, those with chronic kidney disease, and survivors of previous heart attacks or strokes.

“These are the individuals that need to be really worried and take protective measures,” he said.

The study was published July 24 in the journal Circulation.

More information

The U.S. Environmental Protection Agency has more about particle pollution.

SOURCES: Yuewei Liu, PhD, associate professor, epidemiology, Sun Yat-sen University School of Public Health, Guangzhou, China; Sanjay Rajagopalan, MD, chief, cardiovascular medicine, University Hospitals Harrington Heart and Vascular Institute, Cleveland; Circulation, July 25, 2023