PHILADELPHIA — Exercising for two and a half hours a week can reduce a woman's chance of developing endometrial cancer by 34 percent, according to a new study.

Endometrial cancer begins in the cells lining the uterus.

Moderate to rigorous exercise — including brisk walking, running or cycling — may decrease the risk of cancer by improving circulating levels of hormones and reducing body fat, said study researcher Hannah Arem, a doctoral student at Yale School of Public Health.

The finding applies to women of normal weight and who are overweight, researchers said.

''Our results clearly show that women who are active have lower risk'' of developing endometrial cancer, Arem told MyHealthNewsDaily. ''In that sense, we think that if you're active, regardless of your BMI, you'll be at lower risk.'' BMI is body mass index.

Researchers asked 668 women with endometrial cancer and 665 other women about their exercise habits. They rated the women's exercise habits by intensity, using a standardized scale called the Compendium of Physical Activity.

On average, women who exercised at a moderate to vigorous intensity for 150 or more minutes a week had a 34 percent lower risk of having endometrial cancer than women who didn't exercise at all.

Women who had a BMI of less than 25 — between 18 and 25 is considered the normal range — and who exercised for 150 minutes a week had a 73 percent lower risk of developing endometrial cancer than inactive women who were overweight (with a BMI over 25).

The study also showed that overweight women benefited from exercising 150 minutes or more a week — they had a 52 percent lower risk of endometrial cancer than overweight women who didn't exercise.

The finding ''shows that physical activity has an independent effect,'' Arem said.

The National Cancer Institute estimates there will be 43,70 new cases of endometrial cancer in the United States this year, and 7.950 women will die of the disease.

Arem said she and her colleagues next hope to identify the biological mechanisms behind the link between exercise and hormone levels in the blood.

The study was presented here today (Nov. 9) at the Frontiers in Cancer Prevention Research Conference, held by the American Association for Cancer Research.

This article was provided by MyHealthNewsDaily, a sister site to LiveScience.