NEW YORK (Reuters Health) - Strokes occur more often in the spring than any other season, and the heightened risk is seen in men, women, young and old alike, new research suggests.
In a study of Japanese adults who had suffered a stroke between 1988 and 2001, researchers found that the risk of having a stroke in the spring was roughly one-quarter higher than it was in the summer.
Men and women, and adults older or young than 65, all saw their stroke rise in the spring compared with all other seasons.
The findings, reported in the journal Stroke, are in line with some past studies showing that stroke rates tend to be higher in the colder months of winter and spring.
In this study, stroke risk was highest in March, April and May, regardless of known risk factors like high blood pressure, smoking and diabetes.
"The mechanisms underlying seasonal variation of strokes are not fully understood," write Dr. Tanvir Chowdhury Turin of Shiga University of Medical Science, Japan, and colleagues.
However, they note that blood pressure is known to have a similar seasonal variation. If blood pressure is consistently elevated during colder months, that could contribute to the excess strokes seen in the spring.
Similarly, there is evidence that blood may be more prone to clotting during the colder seasons; blood cholesterol levels tend to be higher at that time of year, as do levels of certain blood proteins and blood cells involved in inflammation and clotting.
Influenza, or other respiratory infections, could also play a role, Turin's team points out. The flu, which peaks in the winter to early spring, can worsen chronic medical conditions, including atherosclerosis -- the build-up of artery-clogging plaques that can lead to heart attack or stroke.
Finding out why stroke rates vary by season will be important, according to Turin's team, as that could point to ways to lower the risk.
SOURCE: Stroke, March 2008.