H eres more motivation to get going on a program of regular physical activity: A new National Cancer Institute re- view of 14 prior studies reports that women who regularly exercise reduced their risk of endometrial cancer by about 30%. On the other hand, women who spend more of their day sitting were at greater risk of the can- cer, which affects the lining of the uterus.
Physical activity has been hypothesized to reduce endometrial cancer risk, but this relationship has been diffcult to confrm because of a limited number of prospective studies, explained Steven Moore, MD, and col- leagues in the British Journal of Cancer. Scientists already knew that maintaining a healthy body weight is an important way to reduce the risk of endometrial cancer, but it was less clear whether exercise also has an independent ben- eft. A furry of new cohort studies inspired the researchers to take a fresh look and conduct a meta-analysis of the evidence.
We found that physical activity was clearly associated with reduced risk of en- dometrial cancer, Dr. Moore and colleagues concluded. One possible explanation: Keeping active helps lower potentially harmful levels of estrogen, which can increase tumor risk.
The researchers went on, Taken together with the established biological plausibility of this relation, the totality of evidence now convincingly indicates that physical activity prevents or reduces risk of endometrial cancer.
Its not clear, though, just how much exercise women need to enjoy a protective beneft. One of the studies analyzed showed that 20% of endometrial cancers could have been prevented if women had exercised vigorously for about 20 minutes at least fve times a week.
D r. Moore and colleagues went on to investigate sitting time in relation to endometrial cancer risk, using data from the NIH-AARP Diet and Health Study. They found that, independent of exercise levels, greater sitting time was associated with increased endometrial cancer risk. Women who sit more than nine hours a day, for example, were at double the risk of the cancer, compared to those sitting fewer than three hours daily.
The researchers concluded, Limiting time in sedentary behaviors may comple- ment increasing levels of moderate-to-vigor- ous physical activity as a means of reducing endometrial cancer risk.
Women in developed nations have about a 1 in 40 risk of developing endometrial cancer in their lifetimes. About 43,470 new cases of uterus cancer, most of them start- ing in the lining of the uterus, are diagnosed in the US annually, with 7,950 deaths. British Journal of Cancer, Sept. 28, 2010; abstract at < www.nature.com/bjc/journal/ v103/n7/abs/6605902a.html>American Cancer Society<www.cancer.org/Cancer/Endometrial- Cancer>