Why are there more heart attacks in cold weather?

We know that shoveling snow can lead to heart attacks. That’s why cardiologists advise that you avoid shoveling snow if you have heart disease.
But what about cold weather? Can an icy clime trigger heart attacks?
According to an observational study in Sweden published in JAMA Cardiology in November, heart attacks are more frequent in subfreezing weather. The researchers linked an increased incidence of heart attacks to lower air temperatures, lower atmospheric pressure, higher wind velocity and shorter durations of sunshine, based on 16 years of medical and weather data.
As an emergency medicine physician in Columbus, Ohio, I can attest that cold temperatures can raise the risk of heart attacks.
Let's look at the science.
When the temperature dips below freezing, people can experience vasoconstriction, which is tightening of the arteries. The blood vessels in your heart actually shrink a bit, which decreases the amount of blood flow to the heart. That can cause problems such as a heart attack.
When you're physically active, your body performs vasodilation, which is opening of the arteries. Blood vessels dilate to provide more blood. But cold weather can constrict the vessels and blood flow can be interrupted.
Children and the elderly can be especially at risk, because they might not be aware or might not be able to sense temperature as well. We definitely know that people who have small blood vessels from coronary disease are at higher risk for heart attack in the cold.
Cold weather makes your heart work harder to keep your body warm, so your heart rate and blood pressure may increase. So it could be that people with coronary heart disease suffer chest pains or discomfort when they're active in the cold.

What can you do?
Know the warning signs of a heart attack. Shortness of breath, sweating, nausea, dizziness, irregular heartbeat and heaviness or cramping in the chest are all signs you might be having heart problems. Women, the elderly and diabetics might get the typical chest pain, but more often they experience atypical and nonspecific symptoms, including fatigue, a fluttering sensation in the chest, flu-like symptoms, and pain in the back, shoulder or jaw.
Here are some other tips:
Limit your exposure in cold weather.
If you go outside, make sure you dress warmly -- wear extra socks, long underwear and several layers on your upper body.

Don’t overheat your body.
If you dress for the cold then increase physical activity, you can overheat. That can cause blood vessels to dilate, leading to low blood pressure for those who have heart conditions. If you feel like you're sweating, get indoors and take a break.
Don’t overexert yourself.
Shoveling snow is a real workout. In the cold, it's much worse on people with heart disease. You could be at risk for a heart attack or heart failure. Shovel the right way -- make sure there's no more than an inch on the ground, and push it, rather than shovel it. Lay down some salt or de-icer on your sidewalk or driveway before the snow arrives to make it easier to shovel.

If you decide to take a walk in the cold, don't overexert your body by walking into a brisk wind. Take it easy.

Avoid nicotine, alcohol and caffeine.
They can narrow the blood vessels, which can cause the issues I've described. 

Call your doctor.
Consult a physician if you have a medical concern or question or if you’re experiencing symptoms of heart disease or diabetes – before you go out to exercise, preferably.

Remember that in addition to cold temperatures, high winds, snow and rain also can steal body heat. Wind chill can be particularly bothersome, because it removes a layer of heat from your body. Wet conditions also can cause the body to lose heat faster than when it's dry out.
Daniel Bachmann is an emergency medicine physician and director of the hyperbaric medicine program at The Ohio State University Wexner Medical Center.