MELISSA BLOCK, host:

Middle-aged women in the U.S. are heavier on average than they were a decade ago, and that is making them more prone to stroke. That's the conclusion of new research reported at this weeks International Stroke Conference in New Orleans.

Researchers compared two studies - one conducted from 1988 to 1994, and another begun five years later. In each, several thousand women answered questions about whether they had ever been diagnosed as having a stroke.

Dr. Amytis Towfighi reported the findings at the New Orleans conference.

Dr. AMYTIS TOWFIGHI (Assistant Professor of Neurology, University of Southern California): What we found is that the stroke prevalence in women aged 35 to 54 in the previous study was 0.6 percent, and in the more recent study, from 1999 to 2004, was 1.8 percent.

So, the stroke prevalence had actually tripled in a decade. Whereas in men, the stroke prevalence have remained stable.

BLOCK: And is it clear to you, you were also looking at women's weight gain, in particular, in belly fat. Is it clear to you that those two things are related? In other words, as middle aged women have put on weight - especially around their middle - that that seems to be correlated with this tripling in the prevalence of stroke.

Dr. TOWFIGHI: Well, the interesting thing about our study is that we found that other traditional risk factors for stroke such as diabetes and high blood pressure had not changed significantly over the years. And the two things that had changed significantly were waist circumference and body mass index, which is a measure of obesity.

In general, women aged 35 to 54 had increased waist circumference by about 4 centimeters and increasing body mass index. In previous studies, these factors have been associated with a stroke risk.

BLOCK: Four centimeters is how many inches?

Dr. TOWFIGHI: Almost 2 inches.

BLOCK: So the increased stroke risk could be independent of higher blood pressure, independent of higher incidence of diabetes. It could be purely related to weight gain and to body fat?

Dr. TOWFIGHI: Absolutely. We controlled for all those other factors, including diabetes, cholesterol, high blood pressure, and found that the one thing that was driving this increase in stroke risk was the waist circumference and body mass index.

BLOCK: Dr. Towfighi, were you surprised when you looked at these numbers and realized not only had there been a tripling among women in the prevalence of stroke, but that women actually had, I think it's about double the incidence of stroke than that men did in this age group of middle-age people.

Dr. TOWFIGHI: Yeah. This one's really surprising to us, because for men in this age group, their stroke problems have remained stable, whereas women have increased significantly.

So, now, women are at much higher stroke risk than men in this age group. And this goes against everything that we have traditionally been taught in general. In the midlife age group, we think that men are at higher risk than women, and then women catch up after menopause. But it looks like things have changed in recent years.

BLOCK: Was it the women who were technically obese who had the highest risk of stroke? I mean, does a very moderate weight gain seem to have any effect?

Dr. TOWFIGHI: So, in the study, we found that even if you're not obese but you're overweight, that will still increase your risk of stroke.

BLOCK: Dr. Towfighi, thanks very much for talking with us.

Dr. TOWFIGHI: You're welcome. Thank you.

BLOCK: Dr. Amytis Towfighi is an assistant professor of neurology at the University of Southern California. She spoke to us from the International Stroke Conference in New Orleans.

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