BMI Gains in Mid-Life May Raise Risks of Postmenopausal Breast Cancer

While body mass index (BMI) at younger ages has been inversely associated with risk, mid-life BMI has been found by previous studies to be consistently and positively associated with risk of postmenopausal breast cancer. Scientists have speculated that in postmenopausal women, estrogen produced in adipose tissue, or body fat, may promote breast cell proliferation.  In the largest study to-date of adult BMI, BMI change, and postmenopausal breast cancer risk, Laura Y. Sue, from the US National Cancer Institute (Maryland, USA), and colleagues looked specifically at increase in BMI and its timing in relation to postmenopausal breast cancer risk.   The researchers analyzed information from 72,007 women enrolled in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial study, ages 55 to 74 years at the study’s start.  Nearly 57% of the study subjects’ BMI increased 5 kg/m2 or more between age 20 and study entry, roughly equating to a woman of average height (5 feet 4 inches [1.63 meters]) gaining approximately 30 pounds [13.6 kilograms].  Women whose BMI increased 5 kg/m2 or more between age 20 and 50 years were at an 88% increased risk of developing postmenopausal breast cancer, as compared with women who reported a stable BMI.  Those women who reported a BMI increase of 5 kg/m2 or more between age 50 and study entry were at 56% increased risk, as compared with women who maintained BMI.  BMI gain both before and after age 50 independently contribute to increased risk of postmenopausal breast cancer. The team urges that: “Our study suggests that, with respect to postmenopausal breast cancer, healthy weight maintenance throughout adulthood is important and that BMI gain from age 20 to age 50 may play a particularly important role in increasing risk.”