NIH Record - National Institutes of Health

Study Associates Obesity with Lower Breast Cancer Risk in Young Women

A woman measuring her stomach
Study finds that different biologic mechanisms may be responsible for causing breast cancer in younger women.

Young women with high body fat have a decreased chance of developing breast cancer before menopause, according to scientists at NIH and their collaborators. The finding, published online in the journal JAMA Oncology, may help researchers better understand the role obesity plays in breast cancer risk.

“It is well known that women who gain weight, particularly after menopause, carry an increased risk of postmenopausal breast cancer,” said Dr. Dale Sandler, co-senior author and head of NIEHS’s Epidemiology Branch. “Our finding that breast cancer risk is not increased in obese premenopausal women, and in fact decreases, points to the possibility that different biologic mechanisms are responsible for causing breast cancer in younger women.”

Sandler said since the development of breast cancer is relatively rare before menopause, researchers previously found it difficult to fully evaluate risk factors in a single study. She added that previous studies suggested risk factors for breast cancer in younger women may not be the same as in older women.

To understand breast cancer risk in women who have not gone through menopause, Sandler and other researchers formed the Premenopausal Breast Cancer Collaborative Group. The international team pooled data from 19 different studies, comprising 758,592 women from around the world. The approach allowed the team to identify risk factors and patterns that would be difficult to detect with a smaller number of women.

While Sandler and her colleagues are unsure why young, premenopausal women with a high BMI appear to be protected against breast cancer, she cautions that young women should not intentionally gain weight to lower their breast cancer risk.

“There are so many health risks associated with being overweight or obese,” Sandler said. “We still believe it is important for women to maintain a healthy weight throughout life.”

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