Extreme heat can double your risk of heart attack, study finds—how to stay safe

The world is facing unprecedented heat, with the hottest day on record being recorded this month. There is also an extreme heat wave happening across the southwest and central U.S. that’s making its way east.Video above: Here’s how to stay safe in record-setting temperaturesWith that comes a very real risk of heat illness like heat exhaustion and heat stroke. But new research finds there’s one more serious health issue to have on your radar in extreme weather: the risk of a deadly heart attack.The study, which was published in the journal Circulation, analyzed data from more than 202,000 heart attack deaths between 2015 and 2020 in Jiangsu province, China. It found that when temperatures were either very high or very low, or when there was a high level of particulate matter pollution in the air, there was a significant risk that someone would die from a heart attack, a.k.a. myocardial infarction. The researchers specifically found that the risk of heart attack was 18% higher than usual during two-day heat waves with temperatures at 82.6 to 97.9 degrees, and 74% higher during four-day heat waves with temperatures ranging from 94.8 to 109.4 degrees. On the other extremes of temperature, the risk of deadly heart attack was 4% higher during two-day cold periods with temperatures at or below 33.33 to 40.5 degrees and 12% higher than usual during three-day cold snaps with temperatures that ranged from 27 to 37.2 degrees. The risk of dying from a heart attack during extreme weather was higher in women than men during heat waves, and higher in people who were 80 and older. “This study provides consistent evidence that exposure to both extreme temperature events and particulate matter is significantly associated with an increased odds of myocardial infarction mortality, especially for women and older adults,” the researchers concluded. But what is it about extreme temperatures that raise your risk of dying from a heart attack, and how can you stay safe in high heat and very cold weather? Here’s what you need to know. How might extreme weather raise your risk of dying from a heart attack? A heart attack is what happens when a part of the heart muscle doesn’t get enough blood, the Centers for Disease Control and Prevention (CDC) explains. There is a huge range of potential risk factors for heart attack, per the CDC, including: High blood pressure Unhealthy cholesterol levels Diabetes ObesityEating a diet high in saturated fats, trans fat, and cholesterolNot getting enough physical activityDrinking too much alcoholTobacco use Having a family history of heart diseaseBut extreme temperatures are definitely a potential risk factor, and there is some precedence for this, says Rigved Tadwalkar, M.D., a board-certified cardiologist at Providence Saint John’s Health Center in Santa Monica, CA. The Environmental Protection Agency (EPA) specifically warns about the impact of high heat on cardiovascular disease, noting that it leads to about a quarter of all heat-related deaths. A 2020 study published in Circulation of temperatures in Kuwait along with mortality data from 2010 to 2016 also found a link between hot temperatures and cardiac deaths, with the highest rates happening when temperatures hit 95 degrees and above. There are a few reasons why extreme heat can impact the heart, Dr. Tadwalkar says. “The main issue is dehydration,” he says. “High temperatures can lead to dehydration due to the loss of bodily fluids, usually through sweating.” That can also cause blood volume to go down, increasing the workload on the heart, he says. At the same time, your body wants to work hard to circulate your blood to keep you from overheating, says Mark Conroy, M.D., an emergency medicine physician at The Ohio State University Wexner Medical Center. "Circulating the blood is necessary to help the body stay cool when combined with sweating and evaporation from the skin," he explains. Extreme heat “can also cause blood to become thicker and that can lead to clotting,” Dr. Tadwalkar says. That, he says, can be "particularly worrisome for those who have preexisting conditions such as coronary artery disease.”Cold weather also has a few factors that can impact the heart. “In cold weather, the body tries to conserve heat by constricting blood vessels—and that can raise blood pressure,” Dr. Tadwalkar says. “For people who already have a history of hypertension, that can be particularly problematic. That in and of itself can increase blood clot formation.” Your body may also raise your heart rate to try to keep you warm, Dr. Conroy says. “This can lead to excess stress on the heart and, in turn, increase risk for heart attacks,” he adds.Stress hormones like epinephrine can spike in cold weather, too, especially if someone isn’t used to it, and that can raise the risk of heart attack, Dr. Tadwalkar says. “There are unfortunate and tragic outcomes with extreme temperatures, particularly with heat waves,” says Scott Kaiser, M.D., a board-certified geriatrician and Director of Geriatric Cognitive Health for the Pacific Neuroscience Institute in Santa Monica, CA. “Often older people are the most at risk.”How to stay safe in extreme temperaturesThe CDC recommends taking a few steps to keep yourself safe in hot weather, including: Stay in an air-conditioned indoor location as much as you can Drink plenty of fluids even if you don’t feel thirsty. Schedule outdoor activities carefully. Wear lightweight, loose-fitting clothes and sunscreen. Take cool showers or baths Check local news for health and safety updatesIn cold weather, the CDC suggests doing the following: Wear appropriate outdoor clothing, including a tightly woven, wind-resistant coat or jacket; inner layers of light, warm clothing, mittens, hats, scarves, and waterproof boots. Work slowly when doing outdoor chores Take an emergency kit and friend when you do outdoor recreation Carry your phone with youDr. Kaiser recommends being “really cautious about physical activity” outside in extreme temperatures and staying inside as much as possible. Dr. Tadwalkar agrees. “You want to avoid sudden exertion or vigorous activity and ramp up things slowly,” he says. “Ultimately, use as much common sense and caution as you can,” Dr. Kaiser says.