Body mass index and physical activity at different ages and risk of multiple myeloma in the NIH-AARP diet and health study.

Several studies have reported an increased risk of multiple myeloma associated with excess body weight. We investigated the risk of multiple myeloma in relation to separate measures of adiposity and energy balance at different ages in the National Institutes of Health-AARP Diet and Health Study, a large prospective cohort study in the United States. Participants completed a baseline questionnaire (1995-1996; n = 485,049), and a subset of participants completed a second questionnaire (1996-1997; n = 305,618) in which we solicited more detailed exposure information. Hazard ratios and 95% confidence intervals were estimated for the risk of multiple myeloma (overall, n = 813; subset, n = 489) in relation to several measures of obesity and leisure time physical activity. Multiple myeloma risk was associated with increasing body mass index (BMI) at cohort entry (per 5-kg/m(2) increase, hazard ratio (HR) = 1.10, 95% confidence interval (CI): 1.00, 1.22); similar associations were observed for BMI at age 50 years (HR = 1.14, 95% CI: 1.02, 1.28), age 35 years (HR = 1.20, 95% CI: 1.05, 1.36), and age 18 years (HR = 1.13, 95% CI: 0.98, 1.32) without adjustment for baseline BMI. Risk of multiple myeloma was not associated with physical activity level at any age. These findings support the hypothesis that excess body weight, both in early adulthood and later in life, is a risk factor for multiple myeloma and suggest that maintaining a healthy body weight throughout life may reduce multiple myeloma risk.