How Cold Weather Can Increase the Risk of Heart Attacks

We all know that cold weather can contribute to many common health conditions, such as colds or the flu. However, a new study shows that more serious health complications also can arise—such as heart attacks.

In November 2018, the journal JAMA Cardiology published a study that examined the relationship between cold weather and heart attacks. Researchers looked at incredibly detailed data from a 15-year period in Sweden using the country’s online cardiac registry, Swedeheart, along with information from the Swedish government’s weather institution. They found that days with below-freezing temperatures had the country’s highest incidence of heart attacks. Days with high wind speeds and shorter durations of sunshine were also associated with a higher risk of citizens having heart attacks.

When I look at this study and its results, I see two areas of potential risk for patients: the actual effects cold temperatures have on the body and people’s activity levels after a sudden winter storm. Both of these factors can combine with tragic results in patients who aren’t properly prepared.

How Cold Affects the Body and Heart

Cold temperatures affect the body in many ways that can increase your heart attack risk. For example, cold causes the body’s blood vessels to constrict, or narrow, especially in the arms and legs. This is called peripheral vasoconstriction, and it’s a phenomenon that allows the body to conserve its core heat for as long as possible by restricting blood flow to the areas farthest from the heart. However, this constriction of the blood vessels causes your blood pressure to increase, which can put added stress on the heart, as it has to force blood throughout your body against higher pressure.

Additionally, colder temperatures cause your blood’s platelets to stick together more than normal. While platelets typically clump together to form clots that help seal bleeding wounds, cold weather can increase your risk for a dangerous blood clot to form inside your body. Also, if you have a buildup of plaque (a hard substance made of fat, cholesterol, calcium, and other substances in your blood) in your arteries, the colder air could increase the risk of that plaque rupturing, which can lead to a heart attack.

All of these factors cause your heart to work harder to pump the exact same amount of blood. Logically, that means people should scale back on their physical exertions during cold weather to take it easy on their hearts.

The Risk from People’s Reactions to Cold Weather

Unfortunately, many people actually increase their physical exertion in the cold, not decrease it, which can dramatically increase their heart attack risk.

Much of the increased physical activity we see relating to cold weather comes from shoveling snow. Most folks don’t realize how stressful shoveling the driveway or walks will be, as their frame of reference is what they were doing in the yard last spring, summer, or fall. Shoveling is a deceptively extreme exertion that many people aren’t used to, especially if they’re not already exercising regularly or otherwise lowering their risk of heart disease. On top of this, most people are driven by completion of the task at hand rather than their body’s signals to rest and take a break. In just a couple hours of shoveling, some people can double or triple their usual daily activity levels.

I attended medical school here at Georgetown, but did my post-graduate medical training in Rochester, N.Y.—an area that routinely sees more than 100 inches of snow during the winter. After a big snowstorm, my colleagues and I would often wonder if we would get a patient in the hospital who had suffered a heart attack after shoveling snow, and we often did. Essentially, if people aren’t getting much exercise on a regular basis, and then they’re shifting into high gear to shovel out driveways and sidewalks after a massive snowstorm, they’re putting their hearts through an extreme stress test. Unfortunately, in many cases, they’re failing that test by having heart attacks.

One interesting item I noticed in the Swedeheart study was that there was a greater increase in heart attacks relating to cold weather in places where the weather changed from warm to cold. In places where it’s always cold, people seemed to tolerate it better, whether their bodies have adapted to the temperatures or whether they’ve adapted their behaviors to the weather.

Whose Hearts are Most at Risk from the Cold?

There are three main levels of heart attack risk relating to the cold and snow. The first level includes people who have been under a doctor’s care for some time for heart disease, heart failure, high blood pressure, high cholesterol, or other heart-related issues, as well as those who have had a heart attack in the past. I put these patients in the lowest risk level because, they’re taking care of themselves —that is, taking their medications, controlling their risk factors, and generally protecting themselves.

The next level up includes people who have recently been diagnosed with heart problems and who are still working with their doctors to optimize their treatment plans. These patients are vulnerable because they may not have a risk factor fully controlled yet, such as their high blood pressure, which can skyrocket after a hard session of shoveling snow or other strenuous activity in the cold.

The people who are at greatest risk are those who never see the risk coming. They’re the people who feel good at rest, but have unknowingly developed severe narrowing in an artery. If they decide to go shovel snow when it’s 20 degrees, the stress on their blood vessels can cause a blockage to rupture, and then they suffer a heart attack. That can be a life-threatening emergency, especially if they’re outside alone.

How to Protect Your Heart from the Cold

The best overall protection for your heart is to take steps to reduce or eliminate major risk factors for heart disease. These steps include:

• If you smoke, stop: The Pulmonary Services department at MedStar Washington Hospital Center can help you quit
• Get enough exercise: The American Heart Association recommends at least 2.5 hours of vigorous exercise per week, which works out to 30 minutes a day, five days a week
• Eat a heart-healthy diet: Consume everything in moderation! Make sure you’re getting a variety of fruits and vegetables, whole grains, low-fat dairy, and other healthy choices, and limit red meats and sweets

If you have high blood pressure and monitor your blood pressure numbers at home, watch your numbers after you’ve been active in the cold. Don’t let them rise too high without taking a break.

While you’re in the cold, pay attention to what you’re doing and how tired you are. Make a conscious effort to limit your activity levels to less than what you normally would do in moderate or warm temperatures. If you must shovel snow, make sure someone knows where you are and can either share the workload or check on you from time to time.

Finally, watch for symptoms that could indicate a heart attack. These symptoms can include:

• Chest pain, discomfort, or pressure
• Pain in other areas of the body, such as the back, neck, or jaw
• Fatigue, lightheadedness, or dizziness
• Nausea, indigestion, heartburn, or pain in the abdomen
• Shortness of breath

If you notice any of these symptoms, call 9-1-1 right away.

Frigid weather can be dangerous for your heart. If you’re at risk for heart disease, get checked out by your primary care doctor or a cardiologist. And when the cold and snow strike, take it slow, don’t overexert yourself, and stay safe out there.