Many studies have linked body weight to breast cancer risk. However, weight affects the risk for pre and postmenopausal women differently [64]. 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 (or 1.3 - 1.6-fold), depending on the degree of overweight [64-66]. 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. (For more on this, click here.)
Even though being overweight seems protective in premenopausal women, weight gain should still be avoided. Nearly 80 percent of breast cancers occur in postmenopausal women, and any weight a woman puts on before menopause will likely be carried into her postmenopausal years. In two very large studies, women were at increased risk of developing postmenopausal breast cancer if they had gained 20 or more pounds after age 18 [65,67].
Body shape may also have an effect on breast cancer risk. Though the findings have not been consistent across studies, there is increasing 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 [68-71].
Updated 08/14/08
