Body mass index throughout adulthood, physical activity, and risk of multiple myeloma: A prospective analysis in three large cohorts

Background: Obesity is the only known modifiable multiple myeloma (MM) risk factor. However, the influence of obesity in earlier or later adulthood and the role of other energy balance correlates in MM development are unclear. Methods: We leveraged repeatedly updated data from the Nurses' Health Study, Health Professionals Follow-up Study, and Women's Health Study cohorts to further explore energy balance measures in MM etiology. Exposures derived from questionnaires included young adult body mass index (BMI), cumulative average BMI, BMI change since young adulthood, and cumulative average physical activity and walking. We assessed MM risk related to those variables with Cox proportional hazard models. Results: We observed 575 incident MM cases in over five million person-years of follow-up across the cohorts. In pooled analyses, MM risk increased 17% per 5 kg/m² increase in cumulative average BMI (95% confidence interval (CI): 1.05, 1.29) and 28% per 5 kg/m² increase in young adult BMI (CI: 1.12, 1.47); adjustment for BMI change since young adulthood did not affect either association. BMI change since young adulthood and cumulative average physical activity and walking were not significantly associated with MM risk. Conclusions: These findings suggest that a high BMI in early and later adulthood are risk factors for MM.