One of the most complicated issues in clinical AD research is how diet contributes to cognitive decline. There is also unfortunately a great deal of mythology in this area.
As a scientist and physician, let me start by saying that we have no evidence that AD can be cured or slowed down by any dietary intervention or dietary supplement at this time.
There is no doubt, however, that diet plays a role in healthy aging and this is certainly as important for brain health as it is for heart health. We have also discovered that a deficiency in non-enzymatic antioxidants in the blood (particularly vitamins A, C, E and carotenoids) is very common among patients with AD and this is likely due to dietary deficiencies. While it is not yet proven that correcting these deficiencies slows or reverses AD, it is reasonable and appropriate clinically to encourage patients to eat a healthy diet, rich in fruits, vegetables and nuts with natural antioxidants. It may also be reasonable to consider gentle supplementation to correct specific deficiencies in specific nutrients for individual patients.
I am particularly wary of supplementing non-enzymatic antioxidants to non-physiologic levels, because this may cause unexpected consequences. Vitamin E in particular at high doses can behave in a pro-oxidant fashion and may actually decrease total antioxidant capacity of the blood (see here, here and here). There is at least one meta-analysis which has associated high-dose vitamin E supplementation with all-cause mortality. For these reasons, I am reluctant to encourage high-doses of any dietary supplement for my patients outside of a clinical study.
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