IRON INTAKE AND THE RISK OF COLORECTAL-CANCER

Prospectively gathered data from the National Health and Nutrition Exa mination Survey I and the National Health Evaluation Follow-Up Study w ere analyzed to evaluate the risk of colorectal cancer due to consumpt ion of iron, Morbidity and mortality data due to colorectal cancer mer e available on 14,407 persons first interviewed in 1971 and followed t hrough 1986, A total of 194 possible colorectal cancers occurred in th is group over the 15-year period, Subsite analysis showed that the ris k of colon cancer due to iron intake was elevated throughout the colon for both men and women, with the highest adjusted risks for the inter quartile range seen in the proximal colon for females (relative risk, 1.51; 95% confidence interval, 1.41-1.60), The risk of rectal cancer w as not significantly elevated for men or women, Elevated serum iron wa s also associated with increased risk; however, this effect was strong est in the distal (rather than proximal) colon and was significant onl y among females (adjusted relative risk, 1.73; 95% confidence interval , 1.03-2.92), The mean transferrin saturation was higher among cases t han controls (30.7 versus 28.7%), but total iron-binding capacity did not seem to predict the occurrence of colorectal cancer, Proportional hazards models confirmed that the effects of iron and serum iron were not confounded by age, gender, energy consumption, fat intake, or othe r known risk factors for colorectal cancer, These data suggest that ir on may confer an increased risk for colorectal cancer, and that the lo calizaton of risk may be attributable to the mode of epithelial exposu re, It seems that luminal exposure to iron increases risk proximally, whereas humoral exposure increases risk distally, These differences ma y be due to such factors as oxidation state, binding proteins and the presence of other cofactors such as bile acids, products of bacterial metabolism.