Vitamin E is a dietary compound that functions as an antioxidant, meaning that it attacks compounds known as 'toxic free radicals.' These compounds are charged particles, and can disrupt both how the cell is structured, and how it operates. They are a normal byproduct of cell function, but when there are too many - either because too many are being produced, or not enough are being detoxified - they can cause progressive damage. Laboratory evidence surrounding the concept that free radicals may contribute to the pathological processes in Alzheimer's disease has led to interest in using vitamin E to treat this disorder.
In addition to this evidence, it has been shown that medications or vitamins which increase the levels of brain catecholamines (these being brain chemicals such as dopamine and adrenaline/epinephrine), and that protect against oxidative damage may reduce the damage to neurons. In this way, it is believed that they could slow the progression of Alzheimer's disease.
Unfortunately, despite the idea sounding like a good one, it has been hard to prove. An important 1997 study by Mary Sano and colleagues, published in the New England Journal of Medicine, seemed to suggest that high dose Vitamin E might be helpful. Since then, however, other studies, in other settings, have raised important concerns about high dose Vitamin E. At present, most authorities agree that there is insufficient evidence that Vitamin E helps in the treatment of people with Alzheimer's disease. Other work is ongoing, especially concerning whether low dose Vitamin E might prevent dementia, but another important study in the New England Journal of Medicine in 2005 by Ronald Petersen and colleagues led to disappointment about the role of Vitamin E even in very early Alzheimer's disease.