Why Your Risk of Having a Fatal Heart Attack Is Higher During Extreme Heat

A city with smog in the air.
Extreme temperatures 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 temperatures can significantly increase your risk of a fatal heart attack.
  • High levels of air pollution, such as smoke from wildfires, can also increase your likelihood of having a fatal heart attack.
  • However, health experts say there are simple steps you can take to reduce your risks.  

According to the National Oceanic and Atmospheric Administration (NOAA), the Earth’s average global temperature was 1.89 degrees F (1.05 degrees C) above average in June, making it the hottest on record.

Wildfires in Canada also contributed to unsafe pollution levels in many areas throughout the US earlier this year.

While this combination has put a damper on outdoor summer plans for many people, it can also significantly increase health risks.

Specifically, new research suggests that extremely hot or cold temperatures may increase the risk of fatal heart attack. Pollution levels can, too.

For the study, published on July 24, 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 that a person would die from a heart attack if temperatures were extremely hot or cold or there were high levels of particulate matter pollution (PM). According to The Centers for Disease Control and Prevention (CDC), PM refers to particles of solids or liquids in the air, such as smoke, dust, or dirt.

The news may not be welcome to people, as the summer of 2023 has seen a return to pre-pandemic travel and big-ticket events like concerns after three years of wrestling with the health and economic fallouts stemming from COVID-19. But doctors say the new research is critical.

“Extreme weather — either hot, cold, or high air pollution — all can have deleterious effects on heart health,” says Dr. William Prabhu, MD, 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.”

Why extreme temperatures affect heart attack risk

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.

“The definition of extremely hot or cold weather can vary depending on the geographical region and local conditions,” says Dr. Rigved Tadwalkar, MD, California-based board-certified cardiologist at Providence Saint John’s Health Center. 

But Tadwalker says 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 says. “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.:

What happens to the body in extreme heat

Ever feel like you’re moving a little slower and breathing heavier in the heat, even if you’re just taking a leisurely stroll from a lounge chair to the diving board? You’re not imagining it.

“Routine tasks, such as lifting, carrying moderately heavy items such as shopping bags, and walking up an incline, are significantly more taxing in extreme heat and can reach the tipping point for a cardiovascular event where they would not have reached that threshold in more moderate temperatures,” says Prabhu. 

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,” says Tadwalkar. “This increased workload places additional stress on the heart.”

Prabhu says this risk increases when people perform high cardiovascular output activities, such as long-distance running or a long hike.

What goes out needs to go back in — in other words, it’s important to replenish fluids in high heat. In hotter temperatures, people can become easily dehydrated, which can increase heart attack risk, Prabhu says. 

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

Tadwalkar agrees 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 says.

What happens to the body in cold weather

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,” says Dr. Raj Dasgupta, MD, 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,” says 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.”

Air pollution and the heart

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

Tadwalkar says 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.

How does one know if the air pollution is too high, putting them at an increased chance of a heart attack? 

“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 says.

AirNow.gov allows people to search air quality by zip code to determine their risk.

Why some individuals are at an increased risk of heart attack 

Tadwalker says that specific populations are at a higher risk for a fatal heart attack during extreme heat or cold or when there are high levels of air pollution. These populations include:

  • People with pre-existing cardiovascular conditions, like coronary artery disease and hypertension
  • Pregnant people
  • People with diabetes
  • Aging individuals

However, Prabhu advises everyone 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 says. “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.”

How to protect yourself in extreme heat

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 says.
  • Find a chill spot. “Seek shade or air-conditioned environments, when possible, to avoid overheating,” Tadwalker says.
  • 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 says. “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 says.
  • Dress cool. Tadwalker says that loose, lightweight clothing allows for better air circulation.
  • Avoid peak heat. Dasgupta says 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.

How to protect yourself in extreme cold

When the weather goes in the opposite direction — extreme cold — experts share it’s still important to protect yourself. Your strategies will be a bit different.

  • Dress warmly. Tadwalker recommends layers to protect exposed skin from frostbite while keeping the body warm. Prabhu agrees and recommends 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 says. “Layer and wear highly breathable base layers, mid-layers, and shells.”
  • Consider moving your workout indoors. While exercising in the cold is OK, you might consider using an app or heading to the gym instead. Dasgupta says 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 says. It’s OK to ask for help, such as from families or neighbors, with these tasks.

Take a breather. Tadwalker suggests listening to your body and taking breaks as needed when engaging in high-exertion activities like shoveling snow or exercising.

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