Lin said up to 2 percent of the world's population have an overactive thyroid, which revs up the metabolism and causes sweating, weight loss, diarrhea and nervousness.
In older adults, hyperthyroidism is associated with atrial fibrillation, which can lead to stroke or sudden cardiac death. However, this relationship has not been documented in younger adults, Lin said.
Another expert, Dr. Larry B. Goldstein, director of the Duke University Stroke Center, doesn't think this study shows a causal relationship between hyperthyroidism and stroke.
"The question is, is this real and what is the potential mechanism?" he said. "The overall risk appears to be relatively small. There would need to be 250 people with hyperthyroidism before one would have a stroke."
Treating the hyperthyroidism would probably eliminate the risk factors associated with the risk of a stroke, Goldstein said.
To learn more about stroke, visit the Stroke Association.
SOURCES: Larry B. Goldstein, M.D., director, Duke University Stroke Center, Durham, N.C.; Majaz Moonis, M.D., director, stroke services, University of Massachusetts, Worcester; April 1, 2010, Stroke, online
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