Young adulthood body mass index and risk of cancer in later adulthood: historical cohort study.

Objective: To investigate the relationship between body mass index (BMI) in young adulthood and cancer incidence and mortality.

Methods: A total of 9,549 men and 2,657 women had weight and height measured while at university (1948-1968). Participants were traced through the National Health Service Central Register, and cancer registration and death certificates were obtained. Cox proportional hazard models were used to estimate hazard ratios (HR) of associations between BMI and cancer incidence and mortality.

Results: The mean age at university was 20 years. During a median follow-up of 49 years, 2,349 deaths occurred, including 55 breast, 111 prostate, and 131 colorectal cancer. There were 1,305 cancer registrations, including 102 breast, 211 prostate, and 125 colorectal cancers. There was weak evidence of an association between BMI and colorectal cancer incidence (adjusted HR per 1 kg/m(2): 1.06, 95% CI: 0.98-1.15) and mortality (HR 1.05, 95% CI: 0.98-1.14). There was no evidence of an association between BMI and either breast or prostate cancer.

Conclusions: Targeting a reduction in obesity in young adulthood may prevent a significant number of colorectal cancer deaths, although whether this relationship is direct or through tracking to later adult BMI has yet to be established.