Does taking vitamin, mineral and fatty acid supplements prevent cognitive decline? A systematic review of randomized controlled trials.

BACKGROUND: Observational studies have shown associations between nutritional status and cognition in later life but evidence from intervention studies is unclear. The present study systematically reviewed the evidence on the effect of nutrient supplementation on cognitive function in people aged >or=65 years.
METHODS: Databases including MEDLINE and EMBASE were searched up to 1 September 2006. Randomized controlled trials using at least one kind of vitamin, mineral or omega-3 fatty acid, evaluating standardized neuropsychological test(s), were included. There were no restrictions on participants' baseline nutritional status or cognitive function. Quality assessment and data abstraction were conducted by one author and checked by another.
RESULTS: Of 4229 articles retrieved, 22 trials (3442 participants) were identified. Many were small, short duration and of poor methodology. Only 16 out of 122 cognitive tests were significantly different between groups. A meta-analysis showed no significant effect of taking B vitamins or antioxidant vitamins on global cognitive function. There was insufficient evidence to evaluate the effect of omega-3 fatty acids on any cognitive domains.
CONCLUSION: There was little evidence of a beneficial effect from taking B vitamins or antioxidant supplements on global cognitive function in later life. Larger-scale randomized controlled trials of longer duration in selected age groups are needed.