At this time, it is still unclear whether high-fiber diet reduces rate of colon cancer. Some observational studies found a reduced risk; however, two recent randomized studies did not find any reduction in colon cancer [N Engl J Med 2000 Apr 20;342(16):1149-55]. A systemic review of five studies involving 4349 patients did not find definitive evidence of reduction either [Cochrane Database Syst Rev 2002;(2):CD003430].
Contrary to a common hypothesis that antioxidant vitamins (vitamins A,C,E) can prevent cancer, randomized controlled trials have shown that these vitamins do not reduce the risk of colon cancer [N Engl Med 1994 Apr 14;330(15):1029-35]. High-dose of vitamin E (>400IU/day) may actually cause harm.
Calcium may protect the epithelium, i.e. inner lining, of colon. Calcium, taken at high dose of 1000mg or more a day, may reduce risk of colon cancer [Cancer Epidemiol Biomarkers Prev. 1998 Feb;7(2):163-8]. It appears that calcium should be taken for a long time to reduce the risk.
In short, calcium of high dose is better than fiber and antioxidant vitamins in reducing the risk of colon cancer.
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