Background: Risk of developing multiple myeloma (MM) rises with age and is greater among men and blacks than among women and whites, respectively, and possibly increased among obese persons. Other risk factors remain poorly understood. By pooling data from two complementary epidemiologic studies, we assessed whether obesity, smoking, or alcohol consumption alters MM risk and whether female reproductive history might explain the lower occurrence of MM in females than in males.
Methods: The Los Angeles County MM Case-Control Study (1985-1992) included 278 incident cases and 278 controls, matched on age, sex, race, and neighborhood of residence at case's diagnosis. We estimated MM risk using conditional logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs). In the prospective California Teachers Study (CTS), 152 women were diagnosed with incident MM between 1995 and 2009; we calculated hazard ratios using Cox proportional hazards analysis. Data from the two studies were pooled using a stratified, nested case-control sampling scheme (10:1 match) for the CTS; conditional logistic regression among 430 cases and 1,798 matched controls was conducted.
Results: Obesity and smoking were not associated with MM risk in the individual or combined studies. Alcohol consumption was associated with decreased MM risk among whites only (pooled OR = 0.66, 95% CI = 0.49-0.90) for ever versus never drinking. Higher gravidity and parity were associated with increased MM risk, with pooled ORs of 1.38 (95 % CI = 1.01-1.90) for ≥3 versus 1-2 pregnancies and 1.50 (95% CI = 1.09-2.06) for ≥3 versus 1-2 live births.
Conclusions: Female reproductive history may modestly alter MM risk, but appears unlikely to explain the sex disparity in incidence. Further investigation in consortial efforts is warranted.