THE BELIEF:

Changes in weather can spur heart attacks.

THE FACTS:

It sounds counterintuitive, but a link between the onset of cold weather and heart attacks has been hypothesized for some time, with an array of possible culprits: inflammation from common colds, the stress and indulgence of the holiday season, and higher blood pressure from narrowed blood vessels. Only in recent years have epidemiological studies looked for a connection, and most have found one.

In 2004, for example, a group of British scientists used data from the World Health Organization to look at changes in weather and heart attack rates in women over 50 in 17 countries on four continents. Their study found that a temperature drop of 9 degrees was associated, in general, with a 7 percent increase in hospital admissions for stroke and a 12 percent rise in admissions for heart attack.

Another study, in France, looked at 700 admissions over two years. It found that in people with hypertension, the risk of suffering a heart attack doubled when the temperature fell below 25. Most studies have had similar findings. But one, by Canadian scientists, that looked at heart attack rates and Chinook winds in Calgary -- which can cause temperatures to swing wildly -- found no relationship.

THE BOTTOM LINE:

Mixed, but most studies suggest that heart attacks rise when the temperature falls.

-- The New York Times