Antioxidant vitamins and colorectal adenoma

Greenberg et al. (July 21 issue)¹ report negative results when three antioxidant vitamins (beta carotene, vitamin C, and vitamin E) were given over a four-year period to test their efficacy in preventing colorectal adenoma, a surrogate outcome for colorectal cancer. The authors suggest that the three-year period between the colonoscopic examinations at year 1 and year 4 may not have been long enough for a change in the incidence of adenoma to be observed and that the interventions used may not have been the correct ones to reduce the incidence. A third explanation is that the interventions.  . .