Have you ever heard that shoveling snow can cause a heart attack? There’s actually some truth to that. The physical exertion of shoveling is certainly a factor, but even people who are used to yard work can be vulnerable: when temperatures hit exceptionally frigid lows, the heart can overwork itself by trying to prevent the body from freezing to death—especially if a preexisting condition is already making the organ pump hard.

A growing body of research is clarifying the link between environmental temperature and heart health. And cold weather is not the only concern. Studies also show that outdoor heat of 108.9 degrees Fahrenheit triples the risk of cardiovascular death. With September 2023 clocking in as the most anomalously hot month in recorded history and with global temperatures projected to increase by 1.5 degrees Celsius (2.7 degrees F) above preindustrial levels by the next decade, heat is becoming a more common threat to heart health.

“Knowing what it does to our physiology, I’m sure we will see an uptick in heart attacks with warmer weather,” says Jennifer Wong, a cardiologist and medical director of noninvasive cardiology at MemorialCare Heart & Vascular Institute in California. She adds that health care centers may also start to see more people with symptoms that could lead to a heart attack, including chest pain, reduced blood flow and an increased heart workload.

There is no way to control the weather, but you do have the power to shield your heart from the elements. Knowing more about the dangers is a good first step.

HOW DOES COLD WEATHER IMPACT THE HEART?

The human body’s core temperature typically ranges from 97.5 to 98.9 degrees F. When intense cold starts to bring this temperature down, the body responds by activating the sympathetic nervous system (which is perhaps best known for setting off a person’s fight-or-flight response). This triggers certain mechanisms to preserve as much heat as possible. One such mechanism is vasoconstriction, which is when the muscles in blood vessel walls narrow to prevent heat loss, says cardiologist Laxmi Mehta of the Ohio State University Wexner Medical Center. Blood, an essential component of thermoregulation, normally distributes heat all over the body; in extreme cold, the sympathetic nervous system reduces blood flow to the skin to preserve warmth in the body.

Vasoconstriction and reduced blood flow keep a person warm, but they also increase blood pressure. Research presented at an American Heart Association conference earlier this year that has not yet been peer-reviewed showed that people were more likely to have increases in systolic pressure (a blood pressure measurement’s “top” reading, which represents the force pushing against the artery walls when the heart contracts) during winter, compared with summer. Elevated pressure forces the heart to work harder to circulate blood throughout the body.

“This strain can increase one’s heart rate and blood pressure, which can result in cardiac symptoms for some people and can even result in heart attacks,” Mehta says. She warns that lower temperatures may also raise the risk of blood clots. This is because blood thickens when cold, potentially causing platelets to stick together in a clot—which in turn increases the risk of heart attack or stroke.

HEART RISK DURING THE HOLIDAY SEASON

The Northern Hemisphere’s winter is a time for some of the biggest holidays of the year—and also for an uptick in heart attacks. A 2018 study in BMJ found people were more likely to experience heart attacks on Christmas Eve, compared with other celebratory events. Cold weather and the extra stress of planning for the holidays, along with traditional indulgence in salty and high-cholesterol meals, could make people forgo their usual heart-healthy diet and activities. These combined factors increase the risk of a heart attack.

“People may eat out more, drink more alcohol, exercise less and sleep less,” Mehta explains. “And the excitement of spending time with family and friends may result in people ignoring symptoms, or they may try to postpone addressing symptoms until after the holidays.”

HOW HEAT HARMS HEART HEALTH

Heat, as well as cold, can threaten core temperature regulation. In response to extreme heat, the sympathetic nervous system increases blood flow to the skin. This, along with vasodilation, or the widening of the blood vessels, helps excess heat dissipate, says Craig Crandall, a professor of internal medicine at the University of Texas Southwestern Medical Center, who studies heat’s effects on the cardiovascular system. But on a hot day, getting more blood to the body’s surface makes the heart work overtime. The heart has to beat faster to circulate two to four times more blood per minute than it would in more comfortable weather.

“Your heart has to work harder because it still needs to put blood into the rest of the body,” Crandall explains. “In addition to that, it also needs to put more blood through the skin to help [the body] cool off.”

If a person continues to feel overheated, Crandall says, their brain will keep on signaling the heart to beat faster—something that the heart cannot sustain indefinitely because a greater demand for blood flow means a greater need for oxygen. Thus, heat stress can overwork the heart muscle into an oxygen-starved state. “That could cause some adverse events, particularly in individuals with various forms of heart disease,” Crandall says. People with clogged arteries, for example, already have trouble supplying their heart with oxygen and other nutrients. The added strain could put them at risk of a heart attack.

HOW TO PROTECT YOUR HEART

During extreme weather, people who can do so should stay indoors and turn up the heat or air conditioner as needed. If you have to go outside, dress appropriately. For those with heart disease, Mehta recommends warming up before going outside in the cold. And if you are doing heavy work such as shoveling snow, take frequent breaks.

Crandall urges people at high risk for heart disease to stay in cool indoor spaces (whether at home or in public) when possible during a heat wave, and he notes that thorough hydration helps the body expel excess heat by sweating.

Finally, most cardiologists agree the best way to avoid weather-related heart attacks is to reduce your risk of heart problems in the first place. Understanding the stress of extreme temperatures on the body and taking appropriate safety measures in these situations is crucial, Wong says. But doing everything you can to prevent heart disease—including exercising, maintaining a heart-healthy diet and taking medication—is just as important.

About the Author(s)

JOCELYN SOLIS-MOREIRA is a freelance journalist covering health and science. She is based in New York State.