Strokes are most common in old age, but new research suggests that lifestyle is putting young people increasingly at risk for stroke too.

In a study of two U.S. states, researchers found the rate of strokes among adults younger than 55 nearly doubled between 1993 and 2005.

Among whites ages 20 to 54, the rate rose from 26 strokes for every 100,000 people, to 48 per 100,000. And among African Americans, it climbed from 83 to 128 per 100,000.

The researchers said they could only speculate on possible explanations. One might be that doctors are detecting strokes in young people more often - both as a result of better brain-imaging technology and of being more vigilant for stroke in the young.

"But I really don't think that's the major reason," said lead researcher Dr. Brett M. Kissela, of the University of Cincinnati College of Medicine. "We're definitely seeing a higher incidence of risk factors for stroke now."

Those risk factors include obesity, diabetes and high blood pressure. "And if you're developing them at the age of 20," Kissela said, "then you may have a stroke at a younger age, too."

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