Effect of vitamin intake on cognitive decline in older adults: Evaluation of the evidence

The objective of this review was to evaluate the evidence from human studies on the intake of vitamins, either as monotherapies or in combination with other vitamins, as neuroprotective agents that may delay the onset of cognitive decline in older adults. Evidence-based methodologies were used to capture and evaluate the highest levels of evidence. The current evidence available showed no association for cognitive benefits of vitamins B6 or B12 as a monotherapy, and recent systematic reviews provide no clear evidence that supplementation with vitamin B6, B12 and/or folic acid improves dementia outcomes or slows cognitive decline, even though it may normalise homocysteine levels. Meta-analyses from systematic reviews have shown an association between low vitamin D levels and diminished cognitive function, although causality cannot be confirmed from the available evidence. There is no convincing evidence for an association of vitamin A, vitamin C or vitamin E either as a monotherapy or in combination with other antioxidant vitamins such as beta-carotene and the prevention of cognitive decline. The appraisal of nineteen systematic reviews and meta-analyses has highlighted the heterogeneity between studies, and the need for better consensus on definitions of cognitive decline, duration of testing and agreement on which specific endpoints are clinically relevant. Evaluation of the totality of the currently available evidence indicates that intake of the above vitamins, either as a monotherapy, or in combination with other vitamins, has no clinically-relevant effect on delaying cognitive decline or delaying the onset of dementia in older adults.