Dual effects of weight and weight gain on breast cancer risk

Weight gain in adulthood may increase a woman's risk of developing breast cancer after menopause. This was one conclusion of a 16-year follow-up of 95,256 women participating in the Nurses' Health Study. During that time, 2,517 women developed breast cancer and 60% were postmenopausal. Weight gain during adulthood did not increase the risk of premenopausal breast cancer but increased the risk of postmenopausal breast cancer two-fold in women who did not use hormone therapy. Weight gain and hormone use combined were linked to one-third of postmenopausal breast cancer cases.
Context.--Breast cancer is a major cause of mortality among women. It is important to identify modifiable risk factors for this disease. Objective.--To examine body mass index (BMI) at the age of 18 years and at midlife and adult weight change in relation to breast cancer incidence and mortality. Design.--Cohort study. Setting.--A cohort of 95 256 US female nurses aged 30 to 55 years who were followed up for 16 years. Main Outcome Measure.--Incident and fatal breast cancer. Results.--During 1 203498 person-years, 2517 incident breast cancers (60% postmenopausal) were documented. Higher current BMI was associated with lower breast cancer incidence before menopause and was minimally associated with incidence after menopause. However, a stronger positive relationship was seen among postmenopausal women who never used hormone replacement (relative risk=1.59 for BMI >31 kg/m[sup.2] vs is less than or equal to 20 kg/m[sup.2]; 95% confidence interval, 1.09-2.32; P for trend Conclusions.--Avoiding adult weight gain may contribute importantly to the prevention of breast cancer after menopause, particularly among women who do not use postmenopausal hormones. JAMA. 1997;278:1407-1411