The incidence of heart attacks is greater during the fall and winter seasons. In fact, studies show that snow shoveling and even the cold weather itself increase heart risks.

A few years ago, Swiss researchers reported that heart disease risk factors — including high blood pressure, cholesterol, and waist circumference — seemed to be higher than average in the winter months (particularly January and February) and lower than average in the summer months (particularly June, July, and August). Weight and blood glucose levels remained the same.

A second study found that the number of heart attacks rose as cold weather set in. They specifically found that each 50°F drop in temperature led to a 7 percent uptick in heart attacks.

The researchers also presented data to the European Society of Cardiology Congress that shows it isn’t simply more heart attacks, but more potentially fatal ones as well. They matched heart attack statistics with temperature changes in Winnipeg, Canada, and found that each 50°F drop in temperature was associated with a 7 percent increased risk of ST elevation myocardial infarction (STEMI) — the most severe form of heart attack. The increase was even predictable with weather forecasts.

Chilly temperatures can also bring on the heartbeat irregularity called atrial fibrillation, which steeply increases the risk of ischemic stroke, the most common type. Taiwanese researchers, who looked at nearly 290,000 patients, found the highest incidence of ischemic stroke in the colder months, and the lowest in the summer months.

Scientists believe that cold weather narrows blood vessels and makes blood clot more readily. Those factors increase the risk of heart attacks and strokes.