Background: While previous studies suggest that overweight, middle-aged men may face increased risk of colon cancer, it is unclear whether their weights as young adults influence this risk. It is also unknown whether their level of physical activity affects their risk of developing colon cancer.
Purpose: To determine the relationship between being overweight in middle-age or young adulthood and colon cancer risk, we prospectively studied alumni of Harvard University. We also investigated whether being overweight influences risk differently for men with different levels of physical activity.
Methods: In 1962 or 1966 (1962/1966), alumni completed questionnaires on weight, height, other sociodemographic characteristics, and medical history. We obtained information on weight and height at college entry from university archives. Alumni (n = 17,595) were followed from 1962/1966 to 1988 for colon cancer occurrence, ascertained from follow-up questionnaires in 1977 and 1988 and death certificates.
Results: Between 1962/1966 and 1988, 302 cases of colon cancer were diagnosed. Colon cancer risk increased with higher levels of Quetelet's index (weight [kg]/height [m]2) in 1962/1966. Relative risk per unit increase, adjusted for age, physical activity, and parental history of cancer, was 1.08 (95% confidence interval [CI], 1.04-1.13). Quetelet's index at college entry did not predict risk as well (adjusted relative risk per unit increase, 1.05; 95% CI, 1.00-1.10). The heaviest fifth of alumni during both college time and in 1962/1966 had almost two and one-half times the risk of the lightest fifth of alumni (adjusted relative risk, 2.40; 95% CI, 1.40-4.13). When alumni were classified according to activity level in 1962/1966, higher levels of Quetelet's index were significantly associated with colon cancer risk only among those who were less active.
Conclusions: Overweight during middle-age or young adulthood is associated with higher colon cancer risk; in overweight, physically active men, however, the risk of colon cancer may not be increased.