Cold weather is a challenge in itself, with travel disruptions, snow and ice making even the simplest tasks take twice as long. But winter also poses a risk to physical health for those who are at a higher risk of heart attack, angina or high blood pressure, because of the ways the body responds to the cold.

A 2021 study in the journal Medicine found that overall, U.S. cardiac arrests peak during December and January, although the exact statistics is difficult to determine. Live Science spoke to experts to find out why.

How does cold weather affect the heart?

Dr. Oliver Guttmann, a consultant cardiologist at The Wellington Hospital, part of HCA Healthcare U.K., told Live Science that cold weather decreases body heat, meaning the heart needs to work harder to keep the body warm. This can increase the chance of a cardiac event in people already at a heightened risk, such as people who smoke and the elderly, he said.

Cold weather also causes blood vessels to narrow around extremities such as fingers and toes, a process known as vasoconstriction, Guttmann said. The result is that the body’s core remains warm and the organs continue working. “With less blood going to extremities like your fingers and toes, there is more pressure to pump blood around the rest of the body,” he said. “[However] this means that your heart has to work harder, increasing both heart rate and blood pressure.”