Weight loss decreases breast cancer risk in postmenopausal women

October is breast cancer awareness month, which an annual campaign to increase the awareness about the deadly disease. With over 2 million new cases every year, it is the most prevalent cancer in women. Although breast cancer runs in families, there are other lifestyle and environmental factors which increase the risk of breast cancer.

Obesity increases the risk of postmenopausal breast cancer; the risk is 1.5 times higher in overweight women and about 2 times in obese women than healthy weight women. The association between weight loss and incidence of breast cancer is inconsistent, and few studies have evaluated the association between the two.

 A recent observational study by Chlebowski RT et al. published in Cancer, the peer-reviewed journal of the American Cancer Society reported that women decreased the risk of breast cancer by 12% if they lost weight in 3 years as compared to the ones whose weight remained stable.

“Obesity is associated with increased risk of incident postmenopausal breast cancer,” Rowan T. Chlebowski, MD, Ph.D., research professor in the department of medical oncology and therapeutics research at City of Hope National Medical Center, and colleagues wrote. “Because approximately one-third of postmenopausal women in the United States are obese, obesity represents a common and potentially modifiable factor related to breast cancer outcome. However, it has not been established that weight loss in postmenopausal women decreases breast cancer incidence or breast cancer mortality.”

The researchers from the Department of Medical Oncology and Therapeutics Research, City of Hope National Medical Center, Duarte, California used data from the Women’s Health Initiative (WHI) Observational Study to study the association.

The study included 61,335 postmenopausal women with no prior history of breast cancer and normal mammogram with body weight and height measured and body mass index (BMI) calculated at baseline and after 3 years.

At the end of 3 years, the analysis was based on 3 weight categories: stable, 5% increase or 5% decrease.

The study participants were between 50 to 79 years, and the mean follow-up duration was 11.4 years, during which the researchers observed 3,061 cases of breast cancer.

Women (n = 8175) who lost weight faced a 12% decreased risk of breast cancer as compared to women whose weight remained stable (n = 41,139) (hazard ratio [HR], 0.88; 95% confidence interval [CI], 0.78‐0.98; P = .02). The association remained the same even after adjustment for mammography.

The mean time to develop breast cancer was 6.5 years after the 3-year weight determination.

Women who gained (≥5%) weight (n = 12,021) were not associated with increased risk of breast cancer (HR, 1.02; 95% CI, 0.93‐1.11) but did show a slightly higher incidence of triple‐negative breast cancer (HR, 1.54; 95% CI, 1.16‐2.05).

“Our study indicates that moderate, relatively short-term weight reduction was associated with a statistically significant reduction in breast cancer risk for postmenopausal women,” said Dr. Chlebowski in Wiley press release. “These are observational results, but they are also supported by randomized clinical trial evidence from the Women's Health Initiative Dietary Modification trial where, in a randomized clinical trial setting, adopting a low-fat dietary pattern that was associated with a similar magnitude of weight loss resulted in a significant improvement in breast cancer overall survival. These findings, taken together, provide strong correlative evidence that a modest weight loss program can impact breast cancer.”

Here is the visual abstract of the study.

Abstract

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