Several studies have linked weight to an increased risk of breast cancer. However, the manner in which weight affects risk differs between pre- and postmenopausal women. Before menopause, it appears that being somewhat overweight decreases a woman’s risk of getting breast cancer. After menopause, however, being overweight increases risk of the disease by about 20% to 60%. This relationship can be explained mainly by the fact that after menopause most of the estrogen in a woman’s body comes from her fat tissue. And the more fat a woman carries after menopause, the more estrogen she will produce, which can increase breast cancer risk.
It’s important to note that even though being overweight seems protective in premenopausal women, women should still avoid weight gain in adulthood. Nearly 80% of breast cancers occur in postmenopausal women, and any weight a woman puts on before menopause will likely carry into her postmenopausal years. A very large study of United States nurses found that gaining 10 or more pounds after age 18 increased the risk of both developing and dying from postmenopausal breast cancer.
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