TUESDAY, April 29 (HealthDay News) -- Increased levels of exercise can reduce but not eliminate the risk of heart disease in overweight and obese women, a U.S. study finds.

The researchers analyzed data from 38,987 women who took part in the recently completed Women's Health Study. At the start of the study in 1992, information was gathered about the women's height and weight, the average amount of time per week they were physically active, other health habits, and medical history. The women were then followed for an average of 10.9 years.

At the start of the study, 34 percent of the women were considered physically active, 31 percent were overweight, and 18 percent were obese.

During the follow-up, 948 of the women developed coronary artery disease. Both body-mass index (BMI) and physical activity levels were individually associated with the risk of heart disease. The risk was lowest for normal weight women who were active, slightly higher for inactive normal-weight women, higher still for active women who were overweight or obese, and highest for inactive overweight or obese women.

Dr. Amy R. Weinstein, of Beth Israel Deaconess Medical Center in Boston, and colleagues noted that fat cells (adipocytes) release chemicals that may harm the heart by accelerating the hardening of the arteries and increasing inflammation, clotting and dysfunction of the blood vessels.

"We postulate that the beneficial effect of physical activity may directly reduce and combat the ill effect of the prothrombotic factors released by adipocytes," the researchers wrote.

But they noted that exercise didn't eliminate the effects of being overweight.

"Even high quantities of physical activity are unlikely to fully reverse the risk of coronary heart disease in overweight and obese women without concurrent weight loss," the study authors concluded. "Regardless of body weight, these data highlight the importance of counseling all women to participate in increasing amounts of regular physical activity and maintaining a healthy weight to reduce the risks of coronary heart disease."

The study was published in the April 28 issue of the Archives of Internal Medicine.

More information

The U.S. National Women's Health Information Center has more about heart disease.

-- Robert Preidt

SOURCE: JAMA/Archives journals, news release, April 28, 2008

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