Nutritional prevention of cancer: new directions for an increasingly complex challenge.

JNCI | Editorials 363 The prospects for cancer prevention through micronutrient supplementation have never looked worse. Several large, randomized cancer prevention trials have recently reported no reduced risk from micronutrient supplementation ( 1 – 4 ), and the short report by Figueiredo et al. in this issue of the Journal adds to a growing body of evidence that micronutrient supplementation may be harmful. Figueiredo et al. have conducted a secondary analysis from a trial that reported previously that folate (1 mg/d) increased the risk of recurrence of an advanced colorectal adenoma by 67% ( 5 ). They have found that folate increased the risk of prostate cancer by 163%. Among studies addressing micronutrient supplementation for the prevention of cancer, only a single randomized trial, testing 1200 mg of calcium for preventing the recurrence of colorectal polyps, has reported a statistically significant and positive result for its primary cancer outcome ( 6 ), whereas large trials testing supplementation with multivitamins, Nutritional Prevention of Cancer: New Directions for an Increasingly Complex Challenge