Associations between BMI in youth and site-specific cancer in men-A cohort study with register linkage.

OBJECTIVE: This study examined BMI in young men and incident site-specific cancer to estimate population attributable fractions due to BMI based on projected obesity prevalence. METHODS: A population-based cohort study with measured height and weight at age 18. Cox regression models assessed linear associations for BMI and included age, year, and site of conscription as well as parental level of education as covariates. RESULTS: Primary analyses were performed in 1,489,115 men, of whom 78,217 subsequently developed cancer during a mean follow-up of 31 years. BMI was linearly associated with risk of developing all 18 site-specific cancers assessed (malignant melanoma; leukemia; myeloma; Hodgkin lymphoma; non-Hodgkin lymphoma; and cancer in the lungs, head and neck, central nervous system, thyroid, esophagus, stomach, pancreas, liver and gallbladder, colon, rectum, kidney, and bladder), in some instances evident at BMI levels usually defined as normal (20-25 kg/m2 ). Higher BMI was associated with lower risk of prostate cancer. The highest hazard ratios and population attributable fractions were seen for some gastrointestinal cancers. CONCLUSIONS: This study reports linear associations between BMI at age 18 and subsequent site-specific cancers, calling for rapid action to stem the obesity epidemic and to prepare the health care system for steep increases in cancer cases.