Study objective: To examine the relation between body mass index (BMI) in young adulthood and subsequent mortality from cancer.

Design: Cohort study.

Setting: University of Glasgow student health service. Weight and height were measured by a physician, and used to calculate BMI.

Participants: 8335 men and 2340 women who attended the student health service while at university between 1948 and 1968, and who were followed up with the NHS central register.

Main results: The main outcome measure was cancer mortality. Three hundred and thirty nine men and 82 women died of cancer during the follow up (mean 41 years). BMI was associated with mortality from all cancers in men and women, although it did not reach conventional statistical significance. The adjusted hazard ratio (HR) (95% CI) per 5 kg/m(2), was 1.22 (0.97 to 1.53) in men and 1.43 (0.95 to 2.16) in women. Two hundred men and 61 women died from cancers not related to smoking. The adjusted HR for mortality from these were 1.36 (1.02 to 1.82) and 1.80 (1.13 to 2.86) respectively. These results are adjusted for height, number of siblings, pulse rate, year of birth, age, smoking, birth order, number of siblings, and age at menarche in women. Site specific analyses, comparing the highest with the lowest quartile of the BMI distribution found increased risks of prostate cancer (n=28) and breast cancer among heavier subjects. No association between BMI and colorectal cancer was found.

Conclusions: BMI in adolescence has lasting implications for risk of cancer mortality in later life. Future research will include measures of BMI throughout the lifecourse, to determine the period of greatest risk of obesity, in terms of cancer mortality.