Some 5,141 men (mean age, 51.3 years) were randomly assigned to receive daily a placebo or the combination of vitamin C 120 mg, vitamin E 30 mg, beta-carotene 6 mg, selenium 100 mcg, and zinc 20 mg for 8 years. During the study, 103 cases of prostate cancer were diagnosed. Overall, there was a nonsignificant 12% reduction in prostate cancer incidence associated with nutrient supplementation (relative risk [RR] = 0.88; 95% CI, 0.60-1.29). However, the effect differed significantly between men with a normal baseline prostate-specific antigen (PSA) level (< 3 mcg/L) and those with elevated PSA. Among men with normal PSA, there was a statistically significant 48% reduction in the incidence of prostate cancer in the supplemented group (RR = 0.52; 95% CI, 0.29-0.92). In men with elevated PSA at baseline (less than 10% of the total study group), supplementation was associated with an increased incidence of prostate cancer of borderline statistical significance (RR = 1.54; 95% CI, 0.87-2.72). Supplementation had no effect on PSA levels.

Comment: This study found that modest doses of vitamins C and E, beta-carotene, selenium, and zinc can substantially reduce the risk of prostate cancer in men with an initially normal PSA level. These results support the findings of a previous double-blind study, in which supplementation with 200 mcg/day of selenium from high-selenium yeast for 4.5 years reduced the incidence of prostate cancer by 63%. The possibility that nutritional supplementation increases the risk of prostate cancer in men with an initially elevated PSA level is cause for concern. However, the increase was not statistically significant, and may have been due to chance.

Moreover, better results might have been achieved if the supplement had been formulated slightly differently. The supplement used in the present study did not contain copper, a nutrient that enhances immune function and might conceivably help prevent cancer. Long-term administration of 20 mg/day of zinc may induce marginal copper deficiency, potentially counterbalancing some of the beneficial effect of the administered nutrients. In addition, beta-carotene promotes the development of lung cancer (and conceivably other types of cancer) in cigarette smokers. A modest dose of pre-formed vitamin A might therefore be preferable to beta-carotene in cigarette smokers.

Meyer F, et al. Antioxidant vitamin and mineral supplementation and prostate cancer prevention in the SU.VI.MAX trial. Int J Cancer 2005;116:182-186.