Vitamins and cognition: what is the evidence?

Vitamin supplements are consumed for their purported health benefits by a large segment of the populations of developed countries. Several indirect strands of evidence suggest that increasing levels of vitamins may improve brain function. These include evidence that individual vitamins are intrinsically involved in the cellular and physiological processes underpinning brain function; that small proportions of the population exhibit biochemical deficiencies in each individual vitamin, suggesting that a much larger proportion have less than optimal overall micronutrient status; and that epidemiological research suggests a relationship between individual vitamins (or the potentially neurotoxic amino acid homocysteine, which is related to B vitamin status), and cognitive function and mood. The related question as to whether direct supplementation with vitamins can therefore improve psychological functioning in cognitively intact individuals has been addressed in a number of studies. The evidence reviewed here suggests that, whereas studies involving supplementation with single vitamins, or restricted ranges of vitamins, have demonstrated equivocal results, evidence from studies involving the administration of broader ranges of vitamins, or multivitamins, suggest potential efficacy in terms of cognitive and psychological functioning. In contrast to the literature investigating restricted ranges of vitamins, most of the evidence regarding multivitamins was collected from healthy, non-elderly samples, suggesting that more research in this population is warranted.