In a new study, researchers found that women who lost weight after age 50 and kept it off had a lower risk of breast cancer than women whose weight remained stable.
The reduction in risk increased with the amount of weight loss and was specific to women not using postmenopausal hormones.
The research was conducted by a team at Harvard T.H. Chan School of Public Health and elsewhere.
In the United States, more than two in three adult women are overweight or obese.
And while high body mass index (BMI) is a big risk factor for postmenopausal breast cancer, there has not been adequate evidence to determine if that risk is reversible by losing excess weight.
To learn more, the team used the Pooling Project of Prospective Studies of Diet and Cancer (DCPP) to estimate the association of sustained weight loss in middle or later adulthood on subsequent breast cancer risk.
Their analysis included more than 180,000 women aged 50 and older from ten prospective studies.
Weight was assessed three times over approximately 10 years: at study enrollment; after about five years; then again about four years later.
The team found women with sustained weight loss had a lower risk of breast cancer than women whose weight remained stable, and the larger the amount of sustained weight loss, the lower was the risk of breast cancer.
Women who lost 2 to 4.5 kg had a 13% lower risk than women with stable weight.
Women who lost 4.5 to 9 kg had a 16% lower risk. Women who lost 9 kg or more had a 26% lower risk.
In addition, women who lost 9 kg or more and gained some (but not all) of the weight back had a lower risk of breast cancer compared with those whose weight remained stable.
The results suggest that even a modest amount of sustained weight loss is associated with lower breast cancer risk for women over 50.
These findings may be a strong motivator for the two-thirds of American women who are overweight to lose some of that weight.
Even if you gain weight after age 50, it is not too late to lower your risk of breast cancer.
The lead author of the study is Lauren Teras, Ph.D.
The study is published in JNCI: Journal of the National Cancer Institute.
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