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Does obesity increase the risk of breast cancer?

Julie A. Blehm, MD
Internal Medicine
Add breast cancer to the list of ways that obesity can impact health. In this video, Dr. Julie Blehm discusses how obesity increases the danger posed by this disease.

The effect of obesity on breast cancer risk depends on a woman's menopausal status. Before menopause, obese women have a lower risk of developing breast cancer than do women of a healthy weight. However, after menopause, obese women have 1.5 times the risk of women of a healthy weight. Obese women are also at increased risk of dying from breast cancer after menopause compared with lean women. Scientists estimate that about 11,000 to 18,000 deaths per year from breast cancer in U.S. women over age 50 might be avoided if women could maintain a body mass index (BMI) less than 25 throughout their adult lives.

Obesity seems to increase the risk of breast cancer only among postmenopausal women who do not use menopausal hormones. Among women who use menopausal hormones, there is no significant difference in breast cancer risk between obese women and women of a healthy weight.

Both the increased risk of developing breast cancer and dying from it after menopause are believed to be due to increased levels of estrogen in obese women. Before menopause, the ovaries are the primary source of estrogen. However, estrogen is also produced in fat tissue and, after menopause, when the ovaries stop producing hormones, fat tissue becomes the most important estrogen source. Estrogen levels in postmenopausal women are 50 to 100 percent higher among heavy versus lean women. Estrogen-sensitive tissues are therefore exposed to more estrogen stimulation in heavy women, leading to a more rapid growth of estrogen-responsive breast tumors. Another factor related to the higher breast cancer death rates in obese women is that breast cancer is more likely to be detected at a later stage in obese women than in lean women. This is because the detection of a breast tumor is more difficult in obese versus lean women.

Weight gain during adulthood has been found to be the most consistent and strongest predictor of breast cancer risk in studies in which it has been examined. The distribution of body fat may also affect breast cancer risk. Women with a large amount of abdominal fat have a greater breast cancer risk than those whose fat is distributed over the hips, buttocks, and lower extremities.

This answer is based on source information from the National Cancer Institute..

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.