The tables in the Risk Factor Overview present a modest number of reports with generally null results on nutritional antioxidants (vitamins C and E)—based on dietary intake, dietary supplement use, or plasma levels— and risk of Alzheimer disease (AD) and total dementia. Apart from a possible suggestion of benefits of dietary vitamin E on AD risk, these data provide little support for a role of nutritional antioxidants in the prevention of Alzheimer disease. There are several limitations in these studies that could lead to either spurious negative or positive associations, and thus explain the mixed results. It also remains possible that specific types of exposures defined by timing (e.g., in midlife rather than late life), duration (e.g., over many years), or dietary context (e.g., with phytochemicals) might have beneficial effects that could not be detected in the studies reported to date.
The collective findings from current studies do not suggest a protective effect of vitamin C on the risk of developing AD and therefore do not warrant a recommendation of increasing intake of vitamin C in the diet or through supplements to prevent AD. However, individuals might choose to increase intake of vitamin C for other reasons. For vitamin E supplementation, the body of the evidence argues against its use to prevent dementia due to lack of efficacy and potential toxicity. However, dietary vitamin E may be beneficial, and appears to carry little risk of toxicity.
For a review of the putative mechanisms by which these nutritional antioxidants may influence AD risk and detailed commentary on interpreting the findings below in a broader context, please view the Discussion.