Women who had BMIs of at least 25 who were also under 45 at the age of their last menstrual period had about a sixfold increase in risk vs. their normal-weight counterparts.
The researchers suspect that a hormonal imbalance, specifically a lack of progesterone, is likely to blame for the increased risk, Thomas said.
Dr. Diane Yamada, section chief for gynecologic oncology at the University of Chicago Medical Center, said she suspects the "unopposed estrogen" causes the increased risk. Fat tissue, she explained, plays a role in producing estrogen. "People think about estrogen as only coming from the ovaries, but if you have a lot of adipose tissue, you'll have more estrogen."
Whatever the cause, Thomas said these findings highlight the importance of maintaining a healthy weight.
Both doctors said that weight loss can help reduce the risk of endometrial cancer.
"People have to be very aware that obesity not only puts you at risk for heart disease, diabetes, high blood pressure, but also for cancer," said Yamada. "Endometrial cancer is just one of multiple reasons to try to get healthier."
Any woman, overweight or not, who experiences significant changes in her menstrual periods -- such as a period that lasts longer or a heavier flow than usual -- should discuss these changes with her doctor. And, Yamada advised that any postmenopausal woman who develops bleeding should call her doctor right away, because these could be signs of cancer.
To learn more about endometrial cancer, visit the National Cancer Institute.
SOURCES: Cheryll C. Thomas, M.S.P.H., epidemiologist, division of cancer prevention and control, Centers for Dise
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