-Risk reduction linear and specific to women not using postmenopausal hormones
by Zeena Nackerdien PhD, CME Writer, MedPage Today January 15, 2020
Breast cancer remains the most commonly diagnosed cancer worldwide. Obesity is a risk factor for postmenopausal breast cancer, particularly when excess adiposity is located in the abdomen. The question of whether weight loss can reduce breast cancer risk has assumed added importance in the U.S., where more than two out of three adult women are estimated to be either overweight or obese. However, few studies have assessed if the increased breast cancer risk from excess body weight is reversible.
In the Journal of the National Cancer Institute, Lauren R. Teras, PhD, of the American Cancer Society in Atlanta, and colleagues found that women age 50 years or older who lost weight and kept it off had a lower risk of breast cancer compared with those whose weight stayed the same.
A total of 180,885 women from 10 studies in the Pooling Project of Prospective Studies of Diet and Cancer were included in this analysis. Teras and team estimated weight loss changes at three time points before breast cancer follow-up began. The weight-change assessment period included up to 5-year intervals (interval 1 median 5.2 years, interval 2 median 4.0 years) and totaled 10 years. Stable weight was defined as ±2 kg for a given interval. Sustained weight loss was defined as ≥2 kg (4.4 lbs) lost in interval 1 that was not regained in interval 2.
They identified 6,930 breast malignancies over a median follow-up period of 8.3 years.
More weight loss was associated with a lower risk of breast cancer. For instance, women who lost 2 to 4.5 kg (about 4.4 to 10 lbs) had a 13% lower risk of breast cancer compared with those whose weight was stable. Contrasting the two groups further, the researchers found that women who lost 4.5 to 9 kg (10-20 lbs) had a 16% lower risk. That risk reduction increased to 20% for women who lost 9 kg or more (20+ lbs).
Not all was lost when the pounds crept back. Compared with women whose weight remained stable, women who lost 9 kg or more and regained some (but not all) of the weight back still had a lower risk of breast cancer.
The association of breast cancer risk reduction with weight loss was linear and specific among women who were not using postmenopausal hormones at the start of breast cancer follow-up:
- >2-4.5 kg lost: hazard ratio (HR) 0.82, 95% CI 0.70-0.96
- >4.5-<9 kg lost: HR 0.75, 95% CI 0.63-0.90
- ≥9 kg lost: HR 0.68, 95% CI 0.50-0.93
Researchers did not observe similar associations among hormone therapy users. “Sustained weight gain was not associated with breast cancer risk for either group,” the team wrote.
Teras and colleagues pointed out several limitations of the study, including the use of self-reported weight in eight of the 10 cohorts, the possibility of unknown confounders or survival factors, use of data from the 1980s and 1990s when overweight/obesity was lower, and a lack of racial and socioeconomic diversity in the cohorts.
Despite these limitations, “this study addressed the major limitations of previous studies — specifically, to prospectively examine sustained weight loss during middle-to-later adulthood with adequate sample size in a general population study,” the researchers wrote.
Source Reference: Journal of the National Cancer Institute 2019; DOI: 10.1093/jnci/djz226
Study Highlights and Explanation of Findings:
Sustained weight loss of 2 kg or more was associated with a lower risk of breast cancer compared with stable weight among women age ≥50 years who participated in a large prospective study. Women who sustained 9 kg or more of weight loss and were not taking hormone therapy had the lowest breast cancer risk. Women who lost that amount of weight and then regained some of it back were still at a lower risk for breast cancer versus women whose weight remained the same. Researchers stated that the results were especially striking for overweight/obese women.
“Most other patterns of weight change conferred the same breast cancer risk as maintaining stable weight, including women who gained weight in the first 5 years but subsequently lost weight,” the team wrote.
“Mechanistic studies have consistently shown that blood levels of postmenopausal endogenous estrogens are strongly associated with higher BMI and breast cancer risk, and there is evidence to suggest that circulating sex hormone concentrations can be reduced by weight loss,” they added.