Adult Weight Gain Linked to Higher Breast Cancer Risk After Menopause
For immediate release: November 04, 1997
Boston, MA--Researchers from the Harvard School of Public Health and the Brigham and Women's Hospital report that adult weight gain is associated with an increase in breast cancer risk after menopause. Most previous studies have indicated a weak link between obesity and postmenopausal breast cancer risk. The researchers looked at how the influence of weight gain on postmenopausal breast cancer is modified by hormone use. The study, based on data from the Harvard Nurses' Health Study, is reported in this week's Journal of the American Medical Association.
Among women who never used hormones, a weight gain of 45 pounds during adulthood put a woman at twice the breast cancer risk after menopause compared to a woman who had not gained weight. Even much smaller gains were associated with modest increases in risk. This association is not unexpected because plasma estrogen after menopause is derived primarily from body fat. The study also reports that the lowest risk group for postmenopausal breast cancer is women who do not use hormones and who do not have a significant weight gain during adult life. (On average, postmenopausal women who use hormones have a higher potential breast cancer risk compared to women who do not use hormones.)
"A weak association between weight gain and breast cancer risk in previous studies probably occurred because postmenopausal hormone use very likely masked the actual influence of weight gain," states Zhiping Huang, MD, PhD, Harvard School of Public Health and first author on the study. "Together, hormone use and adult weight gain account for about one-third of postmenopausal breast cancer in this population."
The study found that there is a continuous increase in postmenopausal breast cancer risk with adult weight gain. Thus, maintaining lean body weight and avoiding adult weight gain is indicated.
The researchers suggest that women wishing to reduce their risk of postmenopausal breast cancer should avoid gaining weight after age 18. This will also reduce the risk of diabetes, heart disease and many other conditions. "Women are nevertheless faced with difficult choices, for example, whether to use hormones after menopause. But our study strongly suggests that staying within 5 to 10 pounds or so of one's weight at age 18 can potentially lower breast cancer risk," continues Dr. Huang. "With the assistance of a physician who can help a woman understand her overall risk profile, a woman can explore a healthy weight loss program if necessary, coupled with a healthy diet and regular exercise."
The Nurses' Health Study is an on-going prospective study of women, age 30-55 at enrollment in 1976. The study is directed by Frank Speizer, MD, Brigham and Women's Hospital and Harvard Medical School. Subjects were subsequently followed every two years answering questionnaries concerning their diet, lifestyle and health.
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