Body mass index and cancer risk in Korean men and women.

Obesity is associated with diverse health risks, but the role of body weight (BMI) as a risk factor for all and site-specific cancers remains controversial and risks for cancer associated with obesity have not been well-characterized in Asians. Body weight and risk for cancer were examined in a 14-year prospective cohort study of 1,213,829 Koreans aged 30-95 years insured by the National Health Insurance Corporation who had a biennial medical evaluation in 1992-1995. Incidence rates for all cancers and site-specific cancers were examined in relation to BMI. Age- and smoking-status adjusted hazard ratios (HR) with 95% confidence intervals (CI) were examined using the Cox proportional hazards model. For both sexes, the average baseline BMI was 23.2 kg/m(2), and the association of risk for all-cancers with BMI was positive. Obese men (BMI >or= 30 kg/m(2)) were at increased risk for developing the following cancers: stomach (1.31, 1.05-1.64), colon (1.42, 1.02-1.98), liver (1.63, 1.27-2.10) and gallbladder (1.65, 1.11-2.44). Obese women (BMI >or= 30 kg/m(2)) were at increased risk for developing liver cancer (1.39, 1.00-1.94), pancreatic cancer (1.80, 1.14-2.86) and breast cancer among women aged >or=50 years old (1.38, 1.00-1.90). The HRs were comparable in never and ever smokers for all cancers and all specific sites except for lung cancer. For all cancers common to both sexes, the association was significantly weaker (p < 0.01) in females. Our study provides further confirmation of the excess cancer risk associated with obesity. Rising obesity in Asian populations raises concern that increasing numbers of avoidable cancer cases will occur among Asians.