Several prospective studies have found that weight gain starting in the early adult years is associated with an increased risk of postmenopausal breast cancer. Endogenous hormones are a primary factor in breast cancer, and adiposity can alter circulating hormone levels, especially in postmenopausal women. This prospective cohort study, based on data from the Nurses' Health Study, followed 87,143 postmenopausal women 30 to 55 years of age for up to 26 years (from 1976-2002) to discern the influence, if any, of weight change since age 18. Weight change since menopause was estimated in 49,514 women who were followed for as long as 24 years.
A total of 4393 cases of invasive breast cancer were documented in postmenopausal women in this study. The participants had gained an average of 12 kg since age 18 and 3 kg since menopause during an average postmenopausal interval of 11 years. Compared with women who maintained their body weight or gained less than 2 kg since age 18, those who gained weight had a higher body mass index throughout follow up and drank less alcohol. In addition, they were less likely to exercise and to have used postmenopausal hormones (PMH) for longer than 5 years. Women who had gained 25 kg or more since age 18 had a multivariate-adjusted relative risk (RR) of developing invasive breast cancer of 1.45 (95% confidence interval [CI], 1.27-1.66). Weight gainers who had used PMH at any time were at increased risk compared with those never using hormones. For all postmenopausal women and for those who had used PMH at any time, weight loss correlated with a lower risk of breast cancer. Compared with women who maintained their body weight, those who had gained 10 kg or more since menopause were more likely to have breast cancer (RR, 1.18; 95% CI, 1.03-1.35). Women who had never used PMH, who had lost 10 kg or more of body weight since menopause, or who had maintained their weight loss all were at lower risk than those who maintained their weight.
For the total study population, 15% of cases of breast cancer could be attributed to weight gain of 2 kg or more since age 18 and 4.4% to a gain of 2 kg or more since menopause. Population-attributable risks incurred by women not using PMH were 24.2% for weight gain since age 18 and 7.6% for weight gain since menopause.
These findings suggest that weight loss-even if deferred until after menopause-may lower the risk of invasive breast cancer. It is never too late to lose weight.