In a study supported in part by BCRF, researchers found that women over the age of 50 were less likely to be diagnosed with breast cancer if they lost weight and kept it off.
“We found that sustained weight loss of 10 pounds or more was associated with a 25 to 30 percent lower risk of breast cancer compared to women with a stable weight,” explained Walter Willett, MD, DrPH, BCRF investigator and co-author of the study. The effect was greatest in women who were initially overweight or obese.
The study, published in the Journal of the National Cancer Institute, combined data from 10 large prospective cohort studies from the U.S., Australia, and Asia (totaling 180,885 women) to examine the effect of weight loss in healthy women after age 50 on risk of breast cancer. The women provided at least three body weight measurements between 1996 and 2004. Weight loss was categorized as stable weight (less than 4.5 kg* lost), moderate weight loss (between 4.5-9kg), and significant weight loss (more than 9kg).
Key findings of the study
Strongest data to date on the benefit of weight loss and breast cancer risk
Many studies have shown that excess body weight after age 50 increases the risk of breast cancer, which is not surprising because excess body fat is a major source of estrogens in postmenopausal women. This is the strongest data to date to demonstrate the benefit of weight loss in reducing breast cancer risk, and it further suggests that obesity-associated breast cancer risk can be reversed with sustained weight loss.
“These findings provide strong evidence that even after age 50, women who are overweight or obese can reduce their risk of breast cancer by modest, sustained weight loss,” Dr. Willett said.
Because the study combined multiple smaller cohorts, it had the power to identify associations of weight loss and breast cancer risk that may not be detected in smaller studies. Additionally, this is the first study to look at weight loss after age 50 and breast cancer risk, providing evidence that it’s never too late to lose weight and reduce risk.
Understanding obesity and breast cancer risk
Obesity is a growing epidemic not only in the U.S.—where more than 2 out of 3 adult women are overweight or obese (BMI over 25 or 30, respectively)—but globally as well. The World Health Organization estimates that 40 percent of adult women worldwide are overweight. The obesity epidemic is expected to spread as low-resource countries become more affluent and adopt Western diets and lifestyles. Thus, the rise in breast cancer and other obesity-related chronic disease is expected to increase. The findings from the study suggest that weight management can help prevent breast cancer from becoming an epidemic as well, in addition to many other well-documented benefits, such as reducing the risk of heart disease and type 2 diabetes.
Caveats
The study does not show cause and effect, and the authors stress that further studies are needed. The results do not suggest that losing weight will prevent breast cancer in all women.
“These new findings—combined with the known connections between body weight, blood estrogen levels, and breast cancer risk—provide strong evidence that even moderate weight loss later in life can tip risk of breast cancer in a favorable direction,” Dr. Willett explained. “Doing this by increasing physical activity and choosing healthy foods and beverages will have many other benefits as well.”
BCRF researcher Kala Visvanathan, MBBS, FRACP, MHS, was also a co-author of this study.
* A kilogram is equal to 2.2 pounds.
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