Oxidative stress contributes to brain aging. Use of antioxidant vitamins, especially over the long term, might confer cognitive benefits. Grodstein et al added cognitive testing to the Physicians' Health Study II (PHSII), a randomized trial of beta carotene supplements (50 mg, every other day). The PHSII included participants continuing their original beta carotene assignment from the PHS (n = 4052; ages ≥65 years), begun in 1982, and newer recruits randomized as of 1998 (n = 1904; ages ≥65 years). Near the close of the beta carotene arm, the authors assessed general cognition, verbal memory, and category fluency. The authors found no effect of short-term treatment, but among continuing participants from the PHS (mean 18 years of treatment), significantly better overall cognition and verbal memory was found for the beta carotene group compared with the placebo group.