ENERGY-BALANCE AND COLON-CANCER - BEYOND PHYSICAL-ACTIVITY

Low levels of physical activity and high levels of energy intake and b ody mass have all been directly associated with colon cancer. The purp ose of this study was to determine how physical inactivity interacts w ith other components of energy balance (energy intake and body mass) i n determining colon cancer risk, Data were obtained from 2073 first pr imary cases of colon cancer and 2466 age- and sex-matched controls ide ntified from 8 counties in Utah, the Northern California Raiser Perman ente Medical Care Program, and the Twin Cities metropolitan area in Mi nnesota, Recent and lifetime physical activity was assessed by intensi ty of activities performed at home, leisure, and at work; energy intak e was estimated from an extensive diet history questionnaire; and body mass index (BMI) was calculated from measured height at the time of i nterview and reported weight for the referent year. For both men and w omen, lack of lifetime vigorous leisure-time activity was associated w ith increased risk of colon cancer [odds ratio (OR), 1.63 and 95% conf idence interval (CI), 1.26-2.12 for men and OR, 1.59 and 95% CI, 1.21- 2.10 for women, comparing the Lowest to highest level of activity]. Th ere were no differences in risk associated with physical activity by t umor site within the colon or by age at diagnosis. High levels of ener gy intake were also associated with increased risk of colon cancer in men and women (OR, 1.74 and 95% CI, 1.14-2.67 for men and OR, 1.70 and 95% CE, 1.07-2.70 for women). A large BMI was more associated with in creased risk in men (OR, 1.94 and 95% CI, 1.49-2.54) than in women (OR , 1.45 and 95% CI, 1.08-1.94). Those at greatest risk of colon cancer were those who had the most unfavorable energy balance in that they we re physically inactive, had high energy intakes, and had a large BMI ( OR, 3.35 and 95% CI, 2.09-5.35). However, when physical activity was h igh, having a high energy intake and large BMI resulted in a nonsignif icant increased colon cancer risk (OR, 1.28 and 95% CI, 0.81-2.03). Th is pattern was consistent between the sexes, but there was some eviden ce that men may be at higher risk than women, especially older women, as a result of unfavorable energy balance. These results support previ ous findings that physical inactivity, high energy intake, and large b ody mass are associated with increased risk of developing colon cancer . However, energy balance as a whole seems to be associated with risk of colon cancer, These findings suggest systemic metabolic influences on carcinogenesis and have important implications for prevention.