When it comes to heart disease, being fit may be more important than being thin, according to a study of more than 900 women.

"Our study shows that the lack of physical fitness is a stronger risk factor for developing heart disease than being overweight or obese," said Timothy Wessel, a physician at the University of Florida who headed up the research.

The study involved 906 women whose health histories were tracked from 1996 to 2000. Seventy-six percent were overweight at the start of the study, when the mean age of the group was 58.

In addition to being measured for weight, the women were asked about their ability to do common physical activities at home, work and at leisure, such as climbing a flight of stairs, running a short distance or walking around the block without stopping.

During the study, 68 of the women died and 455 suffered a heart disease-related problem such as a heart attack or stroke.

When analyzed by categories of weight and activity, women who were at least moderately active were less likely to develop heart disease or related problems than women with low activity scores, no matter which weight category they were in, according to the study published in this week's Journal of the American Medical Association.

"These results suggest that fitness may be more important than overweight or obesity for cardiovascular risk in women," the study concluded.

Bairey Merz, a physician at Cedars-Sinai Medical Center in Los Angeles and another of the study's authors, said that because physical fitness "has beneficial effects on many factors related to cardiovascular risk, including obesity, increased activity appears to be an ideal therapy for women with coronary heart disease."

He said the American Heart Association endorses at least 30 minutes of moderate-intensity physical activity for women on most or all days of the week.

A second study published in the same journal, however, found that being overweight is a bigger risk factor than inactivity when it comes to adult-onset diabetes among women.

"We observed a modest reduction in the risk of diabetes with increasing physical activity level compared with a large increase in the risk with increasing body mass index," said the report from the Boston VA Healthcare System and Brigham and Women's Hospital.

"Because physical activity is a significant individual predictor and has a beneficial effect on body mass index, it remains an important intervention for diabetes prevention. Our study suggests that to further reduce the risk of diabetes with physical activity, it should be performed in conjunction with achieving weight loss," the study said.

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