Two compounds that experts had hoped might slow or prevent Alzheimer's disease apparently have little or no effect. The result from a long-awaited trial found that vitamin E did not slow the progression from mild cognitive impairment (MCI) to Alzheimer's disease, as had been hoped. Nor did Aricept (donepezil) display any benefit during three years of use.

The good news: Aricept was associated with a slower progression to Alzheimer's during the first year of use.

The Study

The study was designed to see if either Aricept or vitamin E could delay the progression of a type of MCI called amnestic, which is characterize primarily by memory problems.

The researchers randomly assigned 769 patients who had amnestic MCI to receive daily either 2,000 international units (IU) of vitamin E, 10 milligrams (mg) of Aricept or a placebo during the three-year study period.

A total of 212 participants developed possible or probable Alzheimer's during the three years. Researchers found no significant differences between the three study groups in the progression to the disease over the three years.

During the first year, people taking Aricept displayed a reduced likelihood of progressing to Alzheimer's but that benefit did not remain by the end of the third year.

Reaction to Disappointing Results

Dr. Deborah Blacker says the results are "tremendously disappointing. Everyone thought vitamin E would work better earlier, but there's nothing there."

Although Aricept appears to have some benefit in the first year of use, "We're probably seeing a real effect that is transient," Blacker says. The improvement was likely due to a temporarily slowed progression of the disease rather than any actual improvement in symptoms. "It's hard to know what the reason is," she adds.

Aricept and related medicines probably do not have much of an effect on the basic mechanisms driving Alzheimer's, theorizes Dr. Thomas M. Wisniewski, an associate professor of neurology, pathology and psychiatry at New York University School of Medicine. This would also account for why the effect was small and temporary.

While there still may be some use for Aricept, this study essentially dashes any hopes that vitamin E might be able to delay or prevent Alzheimer's. One previous study had suggested it might slow the progression of the disease. However, recent studies have suggested that daily vitamin E supplementation has more side effects than originally thought.

"It makes you less confident that it was totally harmless, which was one of the selling points," Blacker says. "We used to think it was good for general health, and all of those things are being undermined.

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