Antioxidant nutrients and age-related cognitive decline: a systematic review of population-based cohort studies.

PURPOSE: To further inform the debate on the possible cognitive benefits of antioxidant nutrients in the elderly, we systematically reviewed available prospective studies while paying a special attention to their methodological quality.
METHODS: This is a systematic review of studies involving major antioxidant nutrients and change in cognitive performance. Abstracts were independently reviewed; studies were selected based on prespecified criteria. Methodological quality of primary studies was assessed using a methodological checklist for cohort studies. Findings were presented using a narrative synthesis and tabulation of results.
RESULTS: Eight-hundred and fifty potentially eligible studies were identified; 10 met the inclusion criteria and were retained for data extraction and appraisal. The main supportive evidence came from two studies, both judged to be of high quality: The first observed an accelerated decline in global cognition, attention, and psychomotor speed over 9 years, concomitant to a decrease in plasma selenium levels over the same period; the second study reported a slower rate of global cognitive decline over 3 years in persons in the highest quartile of intake of vitamins C, E, and carotenes. All associations persisted after adjustment for confounding factors. Evidence in favor of beneficial associations of higher dietary intake of vitamin E and flavonoids, as well as higher serum beta carotene levels, came from further studies of only adequate quality.
CONCLUSIONS: There is a possibility for protective effects of antioxidant nutrients against decline in cognition in older people although the supportive evidence is still limited in number. This association deserves further examination in additional quality investigations.