No vitamin, supplement, food, or drug has been shown to cure or treat Alzheimer's.
One promising antioxidant, resveratrol, is found in red grapes. But resveratrol also could wind up like vitamin E, vitamin C, ginkgo biloba, B vitamins, and coenzyme Q10. All carried similar hopes at one time or another, but none has been proved to prevent or slow the disease, much less reverse it.
Research suggests your best bet is a diet rich in fruits, vegetables, fish, and nuts to help protect your brain. There’s no silver bullet.