Study Identifies February-April as Stroke Season

BOSTON —  The incidence of strokes appears to vary with the season, and the most common form occurs most frequently in the late winter or early spring, a researcher said Tuesday.

In one of the largest studies of its kind, researchers found that strokes caused by arteries becoming blocked from blood clots or fat--known as infarcts--occur most often from February through April.

“We found a very strong variation in the occurrence of strokes by season,” said Eugene Sobel, an epidemiologist who conducted the study at Temple University School of Medicine in Philadelphia.

Using a register of 600,000 residents of the Lehigh Valley in Pennsylvania, the researchers analyzed 1,944 cases from an 18-month period beginning in July, 1982.

No seasonal association was found with less common types of strokes that are caused by hemorrhages, but infarcts occurred at a rate of about 80 a month from February through April, compared to 60 a month at other times of the year.

The researchers had no explanation of why strokes would follow a seasonal pattern, but they found that lesser attacks, known as transient ischemic attacks, considered warning signs that a major stroke is imminent, also seem to occur seasonally.