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Extreme heat caused by greenhouse gas emissions and air pollution from wildfires can increase your chances of having a fatal heart attack. Selcuk Acar/Anadolu Agency via Getty Images
  • New research suggests extreme heat can significantly increase your risk of a fatal heart attack.
  • Other recent studies have shown that extreme hot and cold temperatures impact cardiovascular-related deaths.
  • High levels of air pollution, such as wildfire smoke, also affect heart disease risk.
  • Health experts say there are simple steps you can take to protect your heart health, even as temperatures become more extreme.

Extreme temperatures caused by greenhouse gas emissions are raising the risk of fatal heart attacks, according to new research. Air pollution has also been linked to an increase in cardiovascular deaths.

A new study published on October 30 in Circulation, the journal of the American Heart Association, found that cardiovascular deaths from extreme heat in the United States could increase by 162% by the middle of the century.

The projected increase is based on a hypothetical scenario in which U.S. policies to lower greenhouse gas emissions have taken effect.

Another scenario with minimal efforts to reduce greenhouse gas emissions predicts that extreme heat-related cardiovascular deaths could increase by 233% anywhere from 2036 to 2065.

The increase in deaths will be greater among older adults and non-Hispanic Black adults, researchers say.

“Climate change and its many manifestations will play an increasingly important role on the health of communities around the world in the coming decades,“ said lead study author Dr. Sameed Khatana, assistant professor of medicine at the University of Pennsylvania and a staff cardiologist at the Philadelphia Veterans Affairs Medical Center, in a press release.

“Climate change is also a health equity issue as it will impact certain individuals and populations to a disproportionate degree and may exacerbate preexisting health disparities in the U.S.,” Khatana continued.

Meanwhile, in another Circulation study published in July, researchers looked at more than 202,000 heart attack deaths in the Chinese province of Jiangsu between 2015 and 2020.

They noted a “significantly associated” risk of a person dying from a heart attack if temperatures were extremely hot or cold, or if there were high levels of particulate matter pollution (PM).

Pollution caused by greenhouse gas emissions and unhealthy levels of particulate matter in the air can have dire health consequences.

Greenhouse gases emit carbon dioxide into the air and contribute to climate change. While greenhouse gases are certainly air pollutants, they are not the same as air pollution caused by particulate matter.

The Centers for Disease Control and Prevention (CDC) defines air particle pollution, or particulate matter (PM), as the particles of solids or liquids in the air, caused by:

  • smoke
  • dust
  • dirt

According to the National Oceanic and Atmospheric Administration (NOAA), July 2023 was the hottest month in 174 years. Wildfires in Canada also contributed to unsafe pollution levels in many areas throughout the U.S. earlier this year.

Greenhouse gas emissions warm the planet and exacerbate the negative health effects of unhealthy levels of fine particulate matter air pollution (PM2.5).

American Heart Association volunteer Dr. Robert Brook, who has co-authored several AHA scientific statements on air pollution noted the role of pollution with excessive heat.

“Fine particulate matter air pollution (PM2.5) causes more than 6 million deaths per year. This study adds to the evidence that the full extent of the harmful effects posed by air pollutants extends beyond PM2.5. By substantially increasing extreme heat days, greenhouse air pollutants pose yet further threats to our well-being,” Brook said in the press release. Brook was not involved in the recent Circulation study.

While air pollution risks often center around the lungs and respiratory health, healthcare providers say it can also affect the heart, largely because the body’s vital organs work together. What affects one can affect another.

“PM2.5 particles are tiny particles that float in the air, risking inhalation deep into the lungs or entrance into the bloodstream,” explained Dr. Rigved Tadwalkar, a board certified cardiologist at Providence Saint John’s Health Center in California.

“Once in the body, these particles can cause inflammation and oxidative stress, leading to damage to blood vessels and the heart.”

Tadwalkar noted that PM2.5 exposure is associated with the development and progression of atherosclerosis, the buildup of plaque in arteries, which increases the risk of heart attacks.

“High pollution days may be classified as those where PM2.5 levels, often measured in micrograms per cubic meter, exceed specific guidelines set by health organizations,” Tadwalkar explained.

AirNow.gov allows people to search air quality by zip code to determine their risk on days when PM2.5 levels are dangerous.

Certain populations are at a higher risk for a fatal heart attack during extreme temperatures or when there are high levels of air pollution. These populations include:

The October 2023 Circulation study noted that older adults and Black individuals in the U.S. face higher risks of cardiovascular-related deaths from climate change due to both medical and environmental factors and racial disparities.

“Previous studies have suggested Black residents may have less access to air conditioning; less tree cover; and a higher degree of the ‘urban heat island effect’ — built-up areas having a greater increase in temperature than surrounding less-developed areas,” Khatana stated.

“Living conditions may also have a role in terms of social isolation, which is experienced by some older adults and has previously been linked with a higher probability of death from extreme heat.”

Researchers and cardiologists agree that extreme temperatures can increase the risk of a fatal heart attack. But there’s no hard-and-fast definition of extreme heat or cold.

“Extreme weather — either hot, cold, or high air pollution — all can have deleterious effects on heart health,” said Dr. William Prabhu, an associate director of the Cardiac Catheterizations Lab with NewYork-Presbyterian Hudson Valley Hospital.

“It is important to consider these stresses and, if present, plan ahead to minimize their effects on heart health.”

“The definition of extremely hot or cold weather can vary depending on the geographical region and local conditions,” Tadwalkar noted, adding that it’s possible to establish a general baseline.

“Taking a broader approach, extremely hot weather would be characterized by temperatures significantly above the average for a given area and season, consistently greater than the 90th percentile,” Tadwalker said.

“Extremely cold weather, on the other hand, would be characterized by temperatures significantly below the average for a given area and season, consistently below the 10th percentile.”

Extreme heat triggers physiological responses to help the body adapt and survive — notably, sweat and dilation of blood vessels close to the skin’s surface.

“This causes the heart to work harder and faster to maintain adequate blood flow to vital organs,” Tadwalkar said. “This increased workload places additional stress on the heart.”

Prabhu noted this risk increases when people perform high cardiovascular output activities, such as long-distance running or a long hike. But even routine tasks can become more taxing in extreme temperatures and increase the risk of a cardiovascular event, Prabhu added.

In hotter temperatures, people can become easily dehydrated, which can increase heart attack risk, Prabhu said.

Dehydration can lead to a syndrome known as syncope, where a person loses consciousness due to lack of blood to the brain,” Prabhu said. “Extremes of heat, particularly dehydration, can exacerbate issues of syncope.”

Tadwalkar agreed that fluid status is an important factor in heart attack risk.

“Dehydration and reduced blood flow to the heart can also indirectly make blood more prone to clotting, potentially leading to blockages in coronary arteries, thus triggering a heart attack,” he said.

Cold weather is also tough on the heart, but for different reasons.

“Cold weather induces vasoconstriction, narrowing the blood vessels, and consequently raises blood pressure levels and reduces the oxygen supply to the heart,” said Dr. Raj Dasgupta, a quadruple board certified physician and Chief Medical Advisor for Sports Illustrated Showcase.

“As your body works to keep you warm, it adds increased stress on your heart.”

Prolonged cold temperatures may cause a person to stay inside and seated more frequently.

“In cold weather, a patient can be sedentary for months then suddenly perform a high output cardiovascular activity, such as shoveling snow,” said Prabhu.

“This effect is so significant that every year during the first snowfall, we know there will be a significant increase in heart attacks related to shoveling snow and typically expect and prepare for that increase in emergency status.”

Prabhu advised that everyone should to take precautions during extreme weather or if there is a high amount of air pollution.

“We will often see young and healthy people who are doing something out of the ordinary for them, such as a marathon or long hike [and] have not adequately prepared as well,” Prabhu said.

“The key is to know your limits and have a low threshold to stop when doing an activity that you don’t do on a regular basis. ‘Start low and go slow’ is a good mantra for activity during extremes of weather.”

To protect yourself in extreme heat, experts recommend:

  • Stay hydrated. “During extreme heat, it is crucial to stay hydrated by drinking plenty of water,” Tadwalker said.
  • Find a chill spot. “Seek shade or air-conditioned environments, when possible, to avoid overheating,” Tadwalker said.
  • Modify your workout. If you plan to work out outdoors, prepare to scale back as needed. “For example, if you typically run 3 miles at a 7-minute mile, maybe try 2 miles at 9-minute miles or walking,” Prabhu said. “It’s OK to curtail your speed and distance in times of extreme weather.”
  • Listen to your body. If you set out on a 5-mile run and aren’t feeling it, take stock and consider pivoting. “Listen to your body and rest in a cool place if you experience warning signs like dizziness or weakness, and seek medical help if symptoms persist or worse,” Dasgupta said.
  • Dress cool. Tadwalker noted that loose, lightweight clothing allows for better air circulation.
  • Avoid peak heat. Dasgupta said it’s usually hottest between 10 a.m. and 4 p.m., and the risk of overexertion and stress on the heart is highest during this period.

Experts share that when the weather goes in the opposite direction — extreme cold — it’s still important to protect yourself.

  • Dress warmly. Tadwalker recommended layers to protect exposed skin from frostbite while keeping the body warm. Prabhu recommended avoiding one common material: Cotton. “It quickly gets wet and heavy and limits our ability to regulate temperature, making your body work much harder just to stay warm,” Prabhu said. “Layer and wear highly breathable base layers, mid-layers, and shells.”
  • Consider moving your workout indoors. While exercising in the cold is OK, consider using an app or heading to the gym instead. Dasgupta said gentle exercises like yoga will help maintain blood circulation.
  • Use caution. “Be cautious during physical tasks, like shoveling snow, to avoid putting too much stress on the heart,“ Dasgupta said.
  • Take a breather. Tadwalker suggested listening to your body and taking breaks when engaging in high-exertion activities like shoveling snow or exercising.