Higher intake of foods rich in vitamin E may modestly reduce long-term risk of dementia and Alzheimers Disease. A key point here is that vitamin E consumed by this study population came from their food, not supplements.
Some examples of foods rich in Vitamin E include wheat germ oil, almonds, sunflower seeds, brazil nuts, mango, spinach, broccoli, tomato, kiwi, avocado, and sweet potato.
Arch Neurol. 2010 Jul;67(7):819-25.