Body weight, breast cancer risk and menopausal status
Many studies have linked body weight to breast cancer risk. However, weight affects risk for pre- and postmenopausal women differently.
- Before menopause, being overweight appears to decrease a woman's risk of breast cancer by 20 to 40 percent [129-131].
- After menopause, being overweight increases the risk by 30 to 60 percent [129-131].
Read Komen’s perspective on body weight and breast cancer risk.
How can body weight affect postmenopausal breast cancer risk?
In premenopausal women, most of the estrogens in the body are produced in the ovaries. However, in postmenopausal women (whose ovaries no longer produce much estrogen), estrogens mainly come from fat tissue.
Fat tissue contains an enzyme called aromatase that converts hormones called androgens (made mostly in the adrenal glands) to estrogens. This extra estrogen likely explains the increased breast cancer risk among postmenopausal women who are overweight.
Learn more about estrogen and breast cancer risk.
Weight gain and breast cancer risk
Although being overweight seems to lower breast cancer risk in premenopausal women, weight gain should be avoided. Most breast cancers occur after menopause, and any weight you gain before menopause you will likely carry into your postmenopausal years.
Gaining weight in adulthood appears to increase a woman’s risk of postmenopausal breast cancer [132]. In the largest study to date, women who gained 20 or more pounds after age 18 had a 15 to 45 percent higher risk of postmenopausal breast cancer compared to women who gained little or no weight [133]. Women who gained 20 or more pounds after menopause had an 18 percent higher risk [133].
Weight loss and breast cancer risk
Losing weight after menopause may help lower risk of breast cancer. One large study found 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 [133]. Not all studies have shown this benefit [134].
Body shape and breast cancer risk
Body shape may also affect breast cancer risk. Though findings are mixed, some findings show women who put on 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 [135-138].
Updated 11/10/11
