Middle-aged women in the U.S. - those between the ages of 35 and 54 - are having more strokes than ever, a trend researchers blame on the growing obesity epidemic.

About 1.8 per cent of women ages 35 to 54 reported suffering a stroke in the most recent federal health survey, from 1999 to 2004. In the previous survey, from 1988 to 1994, only 0.63 per cent reported strokes.

Strokes most often occur in older people, so the sudden spike in middle-age and the reasons behind it are worrisome, say doctors participating at the American Stroke Association's International Stroke Conference 2008.

The tripling of cases in this "pre-stroke population" is "an alarming increase," said Dr. Ralph Sacco, neurology chief at the University of Miami Miller School of Medicine.

The spike in middle-aged strokes happened even though more women in the recent survey were on medications to control their cholesterol and blood pressure -- steps that should lower the risk of stroke.

Almost 15 per cent women in the more recent survey reported using medications to lower blood pressure, compared to 8.9 per cent in the earlier survey. And nearly four percent of women in the more recent survey used medications to lower cholesterol, versus 1.4 percent in the previous survey.

But the biggest difference came with weight, said lead author Dr. Amytis Towfighi, an assistant professor in the Neurology Department at the University of Southern California in Los Angeles, Ca.

Women in the more recent survey were significantly more obese than women a decade prior, with an average BMI of 28.6 versus 27.1 the decade prior.

A BMI of 25.0 to 30.0 is considered overweight, while BMI of 30.1 or more is considered obese.

"In addition, women in the latest survey had an average waist circumference of nearly four centimetres more than women in the earlier study.

"Abdominal obesity is a known predictor of stroke in women and may be a key factor in the midlife stroke surge in women," Towfighi said.