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Antioxidants and Alzheimer's

Causes of Alzheimer's

Alzheimer disease (AD) is the most common cause of dementia in older individuals, accounting for about 60% of dementia cases and affecting at least 3-4 million Americans. The cause of Alzheimer's is thought to be mixed, and involves genetic components, environmental factors, and oxidative stress.

Inheritance patterns for a gene called Apo E appear to influence the development of the disease. In Alzheimer's disease, a type of deposit called neuritic-plaque occurs in the brain. The type of Apo E appears to influence whether neuritic-plaque accumulates and the rate of its development (the types called Apo E3 and E4 increase the risk of Alzheimer's). Reports indicate that only between 50-90% of those that inherit some form of Apo E from both parents go on to develop the condition, confirming that the cause of Alzheimer's involves multiple factors, not just genetics.

Environmental influences are suggested by population and migration studies. Japanese men, for example, have less risk of Alzheimer's than do Americans, unless they immigrate to the US. Other factors speculated to contribute to Alzheimer's include infections, exposure to metals such as aluminum or mercury, or exposure to electromagnetic fields.

Antioxidants C & E

Beta amyloid, the main component of neuritic plaque, is believed to be a source of free radicals. The oxidative stress resulting from an excess of free radicals, in turn, affects the production of other compounds that can ultimately destroy neurons.

Because oxidative stress is thought to play a major role in Alzheimer's, researchers have explored the value of supplemental antioxidants. Fat-soluble vitamin E, in particular, readily enters the brain, where it protects the fats in cell membranes. One double blind trial involving patients with Alzheimer's and moderate dementia found that high dose vitamin E (2000 IU daily) improved clinical characteristics and quality of life (1). Several other observational studies suggest benefit of vitamins C and E in non-Alzheimer's dementia (2) and possibly in reducing the risk of Alzheimer's (3). Two new studies published in June of 2002, also suggest a potential role for these vitamins in delaying the onset or preventing Alzheimer's.

In one study, over 800 people aged 65 or older who were free of Alzheimer's were questioned about how frequently they consumed food sources of vitamins C, E and beta-carotene. Only vitamin E from foods was associated with a reduction in Alzheimer's risk, and only among those volunteers without the Apo E gene (4). In a separate study, some 5300 Alzheimer's-free subjects who were at least 55 years of age were followed an average of 6 years. The subject's dietary intake of beta-carotene, flavonoids, and vitamins C and E was identified. Only higher intake of vitamin E was significantly linked with lower risk, while vitamin C intake reached borderline significance (5). The largest reduction in risk was observed among current smokers.

These studies suggest that higher intake of vitamin E, and possibly vitamin C, may be factors in cutting the risk of AD. Both research teams called for more clinical trials and inquiry to better understand the promising relationship between these antioxidants and Alzheimer's.

1. Sano M, et al. A controlled trial of selegiline, alpha-tocopherol,or both as treatment for Alzheimer's disease. N Eng J Med 336:1216-22,1997.
2. Masaki KH, et al. Association of vitamin E and C supplement use with cognitive function and dementia in elderly men. Neurology 54:1265-72, 2000.
3. Morris MC, et al. Vitamin E and vitamin E supplement use and risk of incident Alzheimer disease. Alzheimer Dis Assoc Disord 12:121-6, 1998.
4. Morris MC, et al. Dietary intake of antioxidant nutrients and the risk of incident Alheimer disease in a biracial community study. JAMA 287:3230-37, 2002.
5. Engelhart MJ, et al. Dietary intake of antioxidants and risk of Alheimer disease. JAMA 287:3223-9, 2002.