Many studies have linked body weight to breast cancer risk. However, weight affects risk for pre and postmenopausal women differently [113]. Before menopause, being overweight appears to decrease a woman's risk of getting breast cancer. After menopause, however, being overweight increases the risk by 30 to 60 percent [113-115]. This relationship can be explained mainly by the fact that fat tissue contains an enzyme called aromatase. This enzyme converts hormones called androgens (made mostly in the adrenal glands) to estrogens, and this extra estrogen can increase breast cancer risk. Learn more about estrogen and breast cancer risk.
Although being overweight seems protective in premenopausal women, weight gain should be avoided. Most breast cancers occur in postmenopausal women, and any weight you put on before menopause you will likely carry into your postmenopausal years. In two large studies, women were at increased risk of postmenopausal breast cancer if they had gained 20 or more pounds after age 18 [114,116].
Losing weight after menopause may help lower risk of breast cancer. One large study found that women who lost four to 11 pounds after menopause had more than a 20 percent lower risk of breast cancer compared to women whose weight did not change [116].
Body shape may also affect breast cancer risk. Though findings are mixed across studies, there is growing evidence that women who put extra weight around their middles (sometimes called "apple-shaped"), as opposed to their hips and thighs (sometimes called "pear-shaped"), have a small to moderate increased risk of breast cancer [117-120].
Updated 11/09/09
