Sustained weight loss lowers risk for breast cancer
Women aged 50 years and older who had sustained weight loss over more than 8 years demonstrated a decreased risk for breast cancer compared with women whose weight remained stable, according to results of a pooled analysis published in Journal of the National Cancer Institute.
Researchers observed the largest decrease among women with sustained weight loss of 9 kg or greater who had not been taking hormone therapy. These women had a 32% lower risk for breast cancer compared with women whose weight remained stable.
“Excess body weight is a known cause of postmenopausal breast cancer, but an important question is, can this be reversed? Believe it or not, this is not something we knew for certain. We had hoped it was true, but the scientific evidence was not there,” Lauren R. Teras, PhD, researcher in the epidemiology research program at American Cancer Society, told Healio. “We have found that losing weight and keeping it off was associated with lower breast cancer risk among women aged 50 years and older. This message is particularly important for the two-thirds of U.S. women who are overweight or obese and therefore at higher risk for breast cancer.”
Teras and colleagues used data from the Pooling Project of Prospective Studies on Diet and Cancer — an international consortium of prospective cohort studies that examined associations between dietary factors and cancer risk among women with no history of cancer, except nonmelanoma skin cancer — to assess associations between sustained weight loss during middle or later adulthood and subsequent breast cancer risk.
The analysis included 180,885 women aged 50 years and older (median age, 59 years; interquartile range [IQR], 55-64) from 10 prospective study cohorts. Weight measurements occurred three times over about 10 years, including at study enrollment, after a median 5.2 years (interval 1) and again after a median 4 years (interval 2).
During median follow-up of 8.3 years (IQR, 6.9-12.8) researchers observed 6,930 cases of breast cancer.
At interval 1, women had a median BMI of 25.1 kg/m² (IQR, 22.7-28.3). By the end of interval 2, median BMI had increased to 25.6 kg/m² (IQR, 22.9-29.1).
About one-fifth of women (20.3%; n = 36,744) maintained stable weight (± 2 kg) during the two intervals, whereas 21.8% (n = 39,371) lost weight during interval 1, although only half of those women (n = 19,694) sustained the weight loss through interval 2. More than one-third of women (n = 67,394) gained weight during interval 1, and the majority (n = 42,912) sustained the weight gain through interval 2.
Results showed women with sustained weight loss had a lower risk for breast cancer compared with women whose weight remained stable (HR = 0.91; 95% CI, 0.81-1.03). Researchers observed greater decreases in risk with larger amounts of sustained weight loss. Women who lost between 2 kg to 4.5 kg had a 13% lower risk (HR = 0.87; 95% CI, 0.77-0.99), those who lost 4.5 kg to 9 kg had a 16% lower risk (HR = 0.84; 95% CI, 0.73-0.96), and those who lost 9 kg or more had a 26% lower risk (HR = 0.74; 95% CI, 0.58-0.94).
Women who lost 9 kg or more during interval 1 and gained some, but not all, of the weight back demonstrated a lower risk for breast cancer than those whose weight remained stable (HR = 0.77; 95% CI, 0.62-0.97).
The reduction in risk with sustained weight loss appeared to be linear and specific to women not using hormone therapy, including those who lost between 2 kg to 4.5 kg (HR = 0.82; 95% CI, 0.7-0.96), those who lost 4.5 kg to 9 kg (HR = 0.75; 95% CI, 0.63-0.9), and those who lost 9 kg or more (HR = 0.68; 95% CI, 0.5-0.93).
“This information equips clinicians with even more health benefits for encouraging their patients to try to lose weight,” Teras told Healio. “However, this study population was predominately white, college educated and largely included U.S.-based cohorts. Future research is needed to confirm these findings in other populations, such as women from different countries, nonwhite populations and women who have a more disadvantaged socioeconomic status.” – by Jennifer Southall
For more information:
Lauren R. Teras, PhD, can be reached at American Cancer Society, 250 Williams St., NW Atlanta, GA 30303; email: firstname.lastname@example.org.
Disclosures: The study was supported by grants from the Breast Cancer Research Foundation and NCI. The authors report no relevant financial disclosures.