However, the research also shows that the popular Alzheimer's drug donepezil may delay the progression to Alzheimer's disease for depressed people with mild cognitive impairment (MCI) or memory problems.
MCI is described as the period in-between normal aging and Alzheimer's disease. A person with MCI experiences memory problems that are greater than expected with normal aging but does not show other symptoms of Alzheimer's disease, such as difficulties in completing everyday activities.
For the study, researchers followed 756 people with MCI who were between the ages of 55 and 91 for three years. Of those, 208 were diagnosed with depression using a test that measures the severity and intensity of a person's depressive symptoms. For every one point increase on the test, a participant's risk of developing Alzheimer's disease went up by three percent.
"Our longer term findings add to the body of evidence that suggests depression is a major risk factor for Alzheimer's disease," said study author Po H. Lu, PsyD, assistant professor of neurology with the David Geffen School of Medicine at UCLA in Los Angeles. "Since the drug donepezil has been shown to improve the behavioral symptoms of Alzheimer's disease, our study also tested whether the drug would delay the progression to Alzheimer's disease in people with memory problems."
Participants were given either vitamin E, donepezil or a placebo pill. The study found that at 1.7 years, among depressed people with mild cognitive impairment, 11 percent of those taking donepezil developed Alzheimer’s disease compared to 25 percent of those who took vitamin E or placebo. At 2.2 years, 14 percent of those taking donepezil developed Alzheimer's compared to 29 percent of those who took vitamin E or placebo. Donepezil had little effect in the group of people who were not depressed.
"If we can delay the progression of this disease for even two years, it could significantly improve the quality of life for many people dealing with memory loss," said Lu.
Donepezil is not approved for use in mild cognitive impairment by the FDA. It is indicated for mild to moderate and severe Alzheimer's disease.
The study was supported by the National Institute on Aging, the Alzheimer's Association, the Alzheimer's Disease Cooperative Study grant, the Alzheimer's Disease Research Center, Jim Easton and the Sidell Kagan Foundation.
The American Academy of Neurology, an association of more than 21,000 neurologists and neuroscience professionals, is dedicated to promoting the highest quality patient-centered neurologic care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as stroke, Alzheimer's disease, epilepsy, Parkinson's disease, and multiple sclerosis.
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