Body Weight and Weight Gain

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 modestly decreases breast cancer risk [128-130].
• After menopause, being overweight increases breast cancer risk [128-130].

Body weight and premenopausal breast cancer risk

Premenopausal women who are overweight have a 20 to 40 percent lower risk of breast cancer than those who are lean [128-130]. This benefit is not well understood and may be limited to estrogen receptor-positive breast cancers [131].

Although being overweight may lower breast cancer risk before menopause, 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.

Body weight and postmenopausal breast cancer risk

Postmenopausal women who are overweight have a 30 to 60 percent higher breast cancer risk than those who are lean [128-130,132].

Being overweight after menopause may increase the risk of estrogen receptor-positive breast cancers more than estrogen receptor-negative cancers. A meta-analysis that combined the results of four studies found postmenopausal women who were heavy had a 70 percent greater risk of estrogen receptor-positive breast cancer compared to those who were lean. However, these heavier women did not have an increased risk of estrogen receptor-negative breast cancers [133].

How can body weight affect postmenopausal breast cancer risk?

In premenopausal women, most estrogens in the body are produced in the ovaries. 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. So, heavier women have higher blood estrogen levels than leaner women [134]. This extra estrogen likely explains at least some of the increased breast cancer risk among postmenopausal women who are overweight. Women with higher estrogen levels have an increased risk of breast cancer compared to women with lower estrogen levels [91].

Learn more about estrogen and breast cancer risk.

Weight gain and breast cancer risk

Gaining weight in adulthood appears to increase a woman’s risk of postmenopausal breast cancer [135]. In the largest study to date, women who gained about 20 pounds after age 18 had a 15 percent higher risk of postmenopausal breast cancer compared to women who gained little or no weight [136]. Women who gained 55 pounds or more after age 18 had a 45 percent higher risk [136].

It’s not just the weight gained from age 18 that seems to be important to risk. Even women who gain weight after menopause appear to increase their risk of breast cancer [136-137]. Findings from the same study showed that women who gained 20 pounds or more after menopause had an 18 percent higher risk of breast cancer compared to those who gained little or no weight after menopause [136].

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 [136]. Not all studies have shown this benefit [138].

Weight loss in adulthood and premenopausal breast cancer risk is under study [139].

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 [140-144].

Updated 11/26/12

Bone Density

Socioeconomic Status