Two widely used treatments for Alzheimer's disease may not be as effective as previously thought, say researchers at the Mayo Clinic in Rochester, Minnesota. The findings, reported online today in the New England Journal of Medicine suggest that vitamin E does not slow a patient's slide from symptoms of memory loss to Alzheimer's, while benefits from the popular drug donepezil are limited to the first year of treatment.
Neurodegenerative diseases such as Alzheimer's are usually preceded by a fuzzy state between memory loss and dementia, known as mild cognitive impairment. Since most treatments are better at preserving nerve function than restoring it, patients likely to get Alzheimer's are typically treated with drugs that slow nerve degeneration. In recent years, donepezil and vitamin E have become the drugs of choice. That's because studies have shown donepezil raises levels of a neurotransmitter needed for memory and learning, while vitamin E is an antioxidant that could repair damage to soft tissue from free reactive oxygen – one of the causes of Alzheimer's. Vitamin E is even used widely as a preventive measure by people with normal brain function.
Ronald C. Petersen and his colleagues at the Mayo Clinic evaluated these two compounds with clinical tests of more than 700 people likely to develop Alzheimer's. For 3 years patients were given varying doses of vitamin E and donepezil. Detailed psychological tests on the patients to measure their mental abilities showed a surprising result: Vitamin E did nothing to prevent Alzheimer's. At the end of 12 months, 38 patients in the placebo group had Alzheimer's compared to 33 from the vitamin E group. Meanwhile, only 16 patients who took donepezil got Alzheimer's. The drug was only effective for a short time, however. At the end of 3 years, the number of Alzheimer's patients in all three groups did not vary significantly.
"This is a very significant report," says Huntington Potter, a neuroscientist with the University of South Florida (USF) in Tampa. "Clearly, antioxidant therapy for neurodegenerative disease may not be as effective as lab research has led us to hope." According to Paula Bickford, also a neuroscientist at USF, it is possible that intervention studies may need to begin before patients experience mild cognitive impairment. She adds, "In some cases getting vitamins from foods has proven more beneficial in delaying the onset of disease than getting vitamins from supplements."