Low temps underlie winter peak in heart deaths

NEW YORK (Reuters Health) - Cold temperature is to blame for the well-known winter peak in the incidence of sudden death due to cardiac causes, according to a new study.

The fact that cold temperatures increase blood pressure and put more strain on the heart is a possible explanation for the increased rate of sudden cardiac death during wintertime. Cold stress may also trigger processes that make blood thicker and increase its ability to clot, which can lead to cardiac events.

Investigators reporting in the Journal of the American College of Cardiology note that seasonality in heart disease events, with a winter peak and summer trough, has long been recognized. Yet, the role of weather conditions is unclear because most studies did not include weather data.

In the new study, researchers looked at the relationship between season, daily temperature, and precipitation in relation to cardiac events over 24 years in Olmsted County, Minnesota -- an area known for its wide range of temperatures throughout the year and extreme winter cold.

Between 1979 and 2002, a total of 2,676 heart attacks and 2,066 sudden cardiac deaths were recorded in the county, report Dr. Yariv Gerber and associates from the Mayo Clinic College of Medicine in Rochester, Minnesota.

According to the team, the risk of sudden cardiac death (when the heart suddenly stops beating), but not heart attack (when a blockage occurs in the arteries supplying blood to the heart), was increased by 17 percent in winter compared with summer. The risk also rose by 20 percent at temperatures below 32 degrees Fahrenheit (0 Celsius) versus 64 to 86 Fahrenheit (18 to 30 Celsius).

The association between cold weather and sudden cardiac death remained stable over the 24-year study period, was similar across age and gender groups and was stronger for individuals without a history of heart disease. Perhaps people free of heart disease were outdoors more in cold temperatures, whereas people with heart conditions might have been advised to avoid outdoor cold stress, the authors suggest.

SOURCE: Journal of the American College of Cardiology, July 18, 2006.