(AP) -- Women who regularly work up a sweat exercising have a 30 percent lower risk of developing endometrial cancer, a new study says.
Researchers at the United States' National Cancer Institute analyzed 14 previous studies and found physical activity cuts the risk of endometrial cancer by 20 to 40 percent when compared to sedentary women. The study was published online Wednesday in the British Journal of Cancer. It was paid for by the National Cancer Institute.
Scientists have long known that exercise cuts your risk of cancers including the breast, colon, esophagus and kidney. Excess body fat sometimes leads to higher hormone levels, which in turn, may elevate the risk of cancer.
"We already knew that maintaining a healthy body weight is an important way to reduce the risk of womb cancer, but our study showed that physical activity has a protective effect of its own," said Steven Moore of the National Cancer Institute, the study's lead author.
But experts still aren't sure exactly how much physical activity is needed to lower their risk. One study showed more than 20 percent of womb cancers could have been avoided if women had exercised vigorously for about 20 minutes at least five times a week.
In related research, Moore and colleagues also considered past studies that tracked how much time women spent sitting. They found women who sat for more than nine hours a day had double the risk of endometrial cancer compared to women who sat fewer than three hours a day. In developed countries, women have about a 1 in 40 chance of getting womb cancer.
"This new research provides clear evidence that the more active women are - and the less time they spend sitting down - the less likely they are to develop womb cancer," said Sara Hiom, director of health information at Cancer Research U.K. She was not linked to the research.
Hiom said exercise helped reduce potentially harmful levels of estrogen. "Keeping active and doing plenty of exercise as well as spending more time on your feet will help reduce the risk of womb cancer."