Sustained Weight Loss and Risk of Breast Cancer in Women 50 Years and Older: A Pooled Analysis of Prospective Data

Abstract

Background: Excess body weight is an established cause of postmenopausal breast cancer, but it is unknown if weight loss reduces risk.

Methods: Associations between weight change and risk of breast cancer were examined among women aged 50 years and older in the Pooling Project of Prospective Studies of Diet and Cancer. In 10 cohorts, weight assessed on three surveys was used to examine weight change patterns over approximately 10 years (interval 1 median = 5.2 years; interval 2 median = 4.0 years). Sustained weight loss was defined as no less than 2 kg lost in interval 1 that was not regained in interval 2. Among 180 885 women, 6930 invasive breast cancers were identified during follow-up.

Results: Compared with women with stable weight (±2 kg), women with sustained weight loss had a lower risk of breast cancer. This risk reduction was linear and specific to women not using postmenopausal hormones (>2-4.5 kg lost: hazard ratio [HR] = 0.82, 95% confidence interval [CI] = 0.70 to 0.96; >4.5-<9 kg lost: HR = 0.75, 95% CI = 0.63 to 0.90; ≥9 kg lost: HR = 0.68, 95% CI = 0.50 to 0.93). Women who lost at least 9 kg and gained back some (but not all) of it were also at a lower risk of breast cancer. Other patterns of weight loss and gain over the two intervals had a similar risk of breast cancer to women with stable weight.

Conclusions: These results suggest that sustained weight loss, even modest amounts, is associated with lower breast cancer risk for women aged 50 years and older. Breast cancer prevention may be a strong weight-loss motivator for the two-thirds of American women who are overweight or obese.

Figure 1.

Schematic of weight loss intervals in relation to breast cancer risk among women aged 50 years and older in the Pooling Project of Prospective Studies of Diet and Cancer. BMI = body mass index; IQR = interquartile range (25th percentile–75th percentile).

Figure 2.

Sustained weight change over approximately 10 years compared with stable weight and risk of breast cancer among women aged 50 years and older not taking postmenopausal hormone therapy in the Pooling Project of Prospective Studies of Diet and Cancer. Weight change was calculated as the difference between reported weight at year 1 and year 2 (interval 1) and year 2 and year 3 (interval 2). The referent group was women with stable weight across both intervals. Sustained weight loss was weight loss in the first interval [median length = 5.2 (interquartile range [IQR] 4.4–5.9) years] that was not regained in the second interval [median length = 4.0 (3.9–4.9) years]. Likewise, sustained weight gain was weight gain in the first interval that was not subsequently lost. Hazard ratios for different amounts of sustained weight loss and gain are indicated by squares, and 95% confidence intervals are indicated by vertical lines.