Is obesity a risk factor?
Obesity (defined as 20% over ideal body weight) is associated with increased breast cancer risk for postmenopausal women. One mechanism for this may be that obesity causes a woman’s fat cells to make extra estrogen, even after her ovaries have stopped producing estrogen themselves. In pre-menopausal women, obesity does not increase breast cancer risk, and may in fact be associated with a decreased risk. In studying breast cancer risk, it can be difficult to separate the effects of obesity from the effects of other behaviors that are associated with obesity. Exercise may decrease estrogen levels, for example, and obese women are less likely to exercise. Thinner women are also more likely to eat a low-fat diet. One theory proposes that such a diet leads to a decrease in the body’s natural estrogen production, and suggests that this may be the mechanism for a decreased breast cancer risk. However, many women who have a low fat diet also exercise and don’t drink. Any of these factors could
