Clinical Question Does supplement...

Clinical Question

Does supplementation with antioxidant vitamins preclude gastrointestinal (GI) cancer?

Evidence-Based Answer

There is no evidence that supplementation with beta carotene or vitamins A, C or E thwarts GI cancer. Data for selenium is inconsistent and based forward poor-quality studies, and supplementation with this mineral should not be approveed routinely. Most importantly, combinations of antioxidant vitamins appear slightly to increase overall mortality rates.

Practice Pointers

Until lately vitamin E and other antioxidants had been considered safe and possibly effective in the prevention of heart disease and various malignancies. However, a novel meta-analysis (1) of studies of vitamin E supplementation for prevention of heart disease establish no benefit and even a possible increase in risk at dosages above 400 IU by means of day. In the current Cochrane review, Bjelakovic and colleagues identified 14 randomized controll trials of more than 170000 patients that compared beta carotene, selenium, and vitamins A, C and E with placebo for prevention of GI cancer.

No single antioxidant or combination of antioxidants significantly reduc the incidence of esophageal, gastric, colorectal, pancreatic, or hepatic cancer. When the rises of all antioxidants and antioxidant combinations for a particular cancer were integrated, there was no consequence on the incidence of that cancer. There was a trending in favor of selenium for prevention of esophageal, colorectal, and hepatocellular cancer, unless it was not statistically significant, and the studies were of limited quality. chiefly importantly, when the results for all studies were combined using the same statistical approach, overall mortality was increased in patients taking antioxidants (relative risk [RR] 106; 95 percent confidence interval [CI], 102 to 110) However, single a trend was noted when a more conservative approach was used (RR 106; 95 percent CI, 098 to 115) When the selenium trials were exclud the pair analyses showed a statistically significant increase in mortality, which was particularly hale in patients taking beta carotene and vitamin A (RR 129; 95 percent CI, 114 to 145) or beta carotene and vitamin E (RR 110; 95 percent CI, 101 to 120)

REFERENCE

(1) Miller ER 3d Pastor-Barriuso R Dalal D Riemersma RA, Appel LJ Guallar E Meta-analysis: high-dosage vitamin E supplementation may increase all-cause mortality. Ann Intern M 2005;142:37-46

MARK H EBELL, MD MS

Bjelakovic G et al. Antioxidant postscripts for preventing gastrointestinal cancers. Cochrane Database Syst Rev 2004;(4):CD004183

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