Body size and composition and colon cancer risk in men.

Several studies of male colon cancer have found positive associations with body size and composition. It is uncertain whether this relationship is due to non-adipose mass, adipose mass, distribution of adipose mass such as central adiposity, or all three. In a prospective cohort study of men aged 27-75 at recruitment in 1990-1994, body measurements were taken by interviewers. Fat mass and fat-free mass (FFM) were estimated from bioelectrical impedance analysis. Waist circumference and waist-to-hips ratio (WHR) estimated central adiposity. Incident colon cancers were ascertained via the population cancer registry. Altogether, 16,556 men contributed 145,433 person-years and 153 colon cancers. Rate ratios (RRs) comparing men in the fourth quartile with those in the first quartile were as follows: FFM 2.3 [95% confidence interval (CI) 1.4-3.7]; height 1.9 (95% CI 1.1-3.1); waist circumference 2.1 (95% CI 1.3-3.5); WHR 2.1 (95% CI 1.3-3.4); fat mass 1.8 (95% CI 1.1-3.0); and body mass index 1.7 (95% CI 1.1-2.8). When continuous measures of FFM and WHR were modeled together, the RR for FFM per 10 kg was 1.37 (95% CI 1.04-1.80) and the RR for WHR per 0.1 unit was 1.65 (95% CI 1.28-2.13). After adjustment for FFM and WHR, the RRs for fat mass and body mass index were no longer statistically significant. Male colon cancer appears to be related to body size and composition by two different pathways, via central adiposity and via non-adipose mass.