Body mass index and risk of multiple myeloma: a meta-analysis of prospective studies.

Excess body weight has been identified as a risk factor for various cancer types. Since the publication of two meta-analyses indicating that body mass index (BMI) is positively associated with the risk of multiple myeloma, the evidence from prospective cohort studies on this issue has largely accumulated. We therefore conducted a meta-analysis to update and expand the previous results. We searched the PubMed and EMBASE databases through 26 January 2011 and reviewed the reference lists of retrieved articles. Prospective cohort studies were included if they reported relative risk (RR) estimates with 95% confidence intervals (CIs) for the association between BMI and multiple myeloma incidence or mortality. A random-effects model was used to combine study-specific results. A total of 15 cohort studies on multiple myeloma incidence and five studies on multiple myeloma mortality were included in the meta-analysis. Compared with subjects in the normal weight category, the risk of multiple myeloma was statistically significantly elevated among subjects categorised as overweight (RR, 1.12; 95% CI, 1.07-1.18) or obese (RR, 1.21; 95% CI, 1.08-1.35). For multiple myeloma mortality, the corresponding summary RR estimates were 1.15 (95% CI, 1.04-1.27) and 1.54 (95% CI, 1.35-1.76). Results from this meta-analysis are in line with the conclusions of the previous meta-analyses, and suggest that excess body weight is a risk factor for multiple myeloma.