Heart-related deaths increase in winter regardless of climate

"This was surprising because climate was thought to be the primary determinant of seasonal variation in death rates," said Bryan Schwartz, M.D., lead author of the study.

Researchers at Good Samaritan Hospital in Los Angeles analyzed 2005-08 death certificate data from seven U.S. locations with different climates: Los Angeles County, Calif.; Texas; Arizona; Georgia; Washington; Pennsylvania and Massachusetts.

In all areas, total and "circulatory" deaths rose an average 26 percent to 36 percent from the summer low to the winter peak over four years.Circulatory deathsinclude fatal heart attack, heart failure, cardiovascular disease and stroke.

Seasonal patterns of total and cardiac deaths were very similar in the seven different climate patterns. Death rates at all sites clustered closely together and no one site was statistically different from any other site.

Researchers didn't design the analysis to determine specific causes that might drive heart-related deaths up in winter. Schwartz hypothesized that colder weather might increase vessel constriction and raise blood pressure.

"In addition, people generally don't live as healthy in winter as they do in summer," said Schwartz, now a cardiology fellow at the University of New Mexico in Albuquerque. "They don't eat as well and don't exercise as much."

However, "people should be extra aware that maintaining healthy behaviors is important in winter," he said.

Schwartz and Robert Kloner, M.D., Ph.D., senior author of the study, used statistical techniques to account for the normal year-to-year temperature differences over the four years. Then, they averaged the resulting four-year data into U-shaped curves for each site and compared them. The graphs showed significant similarities.