Could High BMI Reduce Premenopausal Breast Cancer Risk?

A meta-analysis from the Premenopausal Breast Cancer Collaborative Group investigated the relationship between high body fat and risk with surprising results.


Young women may not want to hear it, but fat could be their friend. Researchers from the Premenopausal Breast Cancer Collaborative Group have found that women aged 18 – 24 years with high body fat have a lower risk of developing breast cancer before menopause.

The researchers pooled data from 19 different studies, involving about 800,000 women from around the world. Overall, 1.7% of the women developed breast cancer. The researchers found that the relative risk of premenopausal breast cancer dropped 12% to 23% for each 5-unit increase in body mass index, depending on age. They saw the strongest effect at ages 18 – 24 years: Very obese women in this age group were 4.2 times less likely to develop premenopausal breast cancer than women with low body mass index (BMI) at the same age.

The researchers do not know why high BMI might protect against breast cancer in some women. Breast cancer is relatively rare before menopause, although previous studies have suggested that the risk factors might be different for younger vs older women, says Dale Sandler, PhD, co-author of the group and head of the Epidemiology Branch at the National Institute of Environmental Health Sciences. For instance, it is well known that women who gain weight, particularly after menopause, have a higher risk. The fact that this study found that the risk not only is not increased, but actually decreased, in younger women points to the possibility that different biologic mechanisms are at work, Sandler says.

Nonetheless, the researchers caution that young women should not intentionally gain weight to offset the risk.

National Institutes of Health. Published June 27, 2018. Accessed July 18, 2018.

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