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Weight Gain in Adulthood Tied to Breast Cancer Risk


 

Women who gain weight either in early adulthood or after menopause are at increased risk for postmenopausal breast cancer, compared with women who maintain a stable weight, reported Dr. A. Heather Eliassen of Harvard Medical School and her associates in the Nurses' Health Study.

Moreover, women who lose weight after menopause decrease their breast cancer risk (JAMA 2006;296:193–201).

The researchers based these conclusions on a prospective analysis of a subset of 49,514 women participating in the Nurses' Health Study, an ongoing survey of women nurses who were premenopausal when they enrolled in 1976 and have been followed since then. All the subjects for this analysis were postmenopausal. Weight change during two time periods—after age 18 and after menopause—was examined.

Compared with women who maintained a stable weight after age 18, those who gained at least 25 kg were at increased risk of developing breast cancer, with an adjusted relative risk of 1.45. Similarly, compared with women who maintained a stable weight after menopause, those who gained at least 10 kg were at increased risk of developing breast cancer, with an adjusted relative risk of 1.18.

Conversely, weight loss during either of those time periods was linked to a decreased risk of breast cancer. However, since relatively few women lost weight, particularly after menopause, “more follow-up is needed to confirm our findings [regarding weight loss] and characterize the benefits more precisely,” Dr. Eliassen and her associates said.

The calculated incidence rate of breast cancer in women who gained at least 25 kg after age 18 was 429 cases per 100,000 person-years, compared with 296 cases in women with stable weight. The calculated incidence rate of breast cancer in women who gained at least 10 kg after menopause was 400 cases per 100,000 person-years, compared with 339 cases in women with stable weight.

“In addition, we estimated that 15% of postmenopausal breast cancer cases in our population may be attributable to weight gain of 2 kg or more since age 18 years, and 4.4% attributable to weight gain of 2 kg or more since menopause,” the researchers said.

These calculations suggest that weight gain during either time period “contributes substantially” to breast cancer incidence, and that many cases of the disease could be avoided by maintaining weight throughout adulthood.

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