Obesity Linked to Breast Cancer Risk
Older women who are obese have a much higher risk of breast cancer because their fat cells release too much estrogen, researchers said Tuesday.
A global study comparing obese women with those of normal weight confirms what doctors have long suspected -- that fat cells release the hormone into the blood, allowing it to help turn normal cells cancerous.
“There was clear hypothesis that the mechanism for the effect of obesity might be high blood estrogen levels, but no one has been able to test that directly,” said Dr. Tim Key of the Cancer Research U.K. Epidemiology Unit at Oxford University.
The researchers report their findings in this week’s issue of the Journal of the National Cancer Institute.
“Women’s risk is affected by many fixed factors -- a family history of the disease, the number of children they have, the age they have their children, when they start their periods and when they stop,” Key said. “But obesity is something that women have a level of control over. Put simply, maintaining a healthy weight avoids extra breast cancer risk for these women.”
Key and colleagues in Britain, Italy, Japan and the U.S. studied eight groups of women past menopause, when the risk of breast cancer rises dramatically. None of the women had cancer and none was taking hormone replacement therapy when blood samples were first taken.
During the study, 624 women developed breast cancer. Hormones in their blood were compared with those of 1,640 cancer-free women of the same age. The more the women weighed, the higher their cancer risk. And the more the women weighed, the higher their levels of a form of estrogen called estradiol.
A woman who was obese, with a body mass index of 30 or more, had an 18% higher chance of breast cancer than a woman with a BMI of 25, which is just on the border of being overweight.
Body mass index compares weight to height, giving a broad range of healthy weights.
With 40% of U.S. women now obese, breast cancer, already the No. 2 cancer killer of women after lung cancer, could become an even worse problem, the researchers said.
