Dietary antioxidants, cognitive function and dementia--a systematic review.

Antioxidant compounds, contained in fruit, vegetables and tea, have been postulated to have a protective effect against age-related cognitive decline by combating oxidative stress. However, recent research on this subject has been conflicting. The aim of this systematic review was to consider current epidemiological and longitudinal evidence for an association between habitual dietary intake of antioxidants and cognition, with consideration given to both cognitive functioning and risk for dementia and its subtypes, including Alzheimer's disease and vascular dementia. Searches of electronic databases were undertaken to identify peer-reviewed journal articles that reported on associations between antioxidant intakes (vitamins C, E, flavonoids, carotenoids) and cognitive function or risk for dementia. Eight cross-sectional and 13 longitudinal studies were identified and included in the review. There were mixed findings for the association between antioxidant intake, cognition and risk of dementia and Alzheimer's disease. Large heterogeneity in study design, differential control of confounders, insufficient measures of cognitive performance, and difficulties associated with dietary assessment may contribute to the inconsistent findings. Overall, findings do not consistently show habitual intakes of dietary antioxidants are associated with better cognitive performance or a reduced risk for dementia. Future intervention trials are warranted to elucidate the effects of a high intake of dietary antioxidants on cognitive functioning, and to explore effects within a whole dietary pattern.