Researchers also found, however, that the popular Alzheimer's drug donepezil may help delay the progression to Alzheimer's in depressed individuals who suffer from mild cognitive impairment or memory problems.
Mild cognitive impairment is the transition period between the cognitive decline of normal aging and Alzheimer's disease. People with mild cognitive impairment experience memory problems that are greater than expected from normal aging but do not show other symptoms of Alzheimer's, such as difficulties completing everyday activities.
The study appears in the June 16 issue of Neurology, the medical journal of the American Academy of Neurology.
The three-year study followed 756 people between the ages of 55 and 91 who had mild cognitive impairment. Of those, 208 were diagnosed with depression using a test that measures the severity and intensity of depressive symptoms. For every one-point increase on the test, a participant's risk of developing Alzheimer's went up by 3 percent.
"Our longer-term findings add to the body of evidence that suggests depression is a major risk factor for Alzheimer's disease," said Po H. Lu, an assistant professor of neurology and a member of the UCLA Mary S. Easton Center for Alzheimer's Disease Research. "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."
Study participants were given either vitamin E, donepezil or a placebo pill. Researchers found that among depressed people with mild cognitive impairment, 11 percent of those taking donepezil developed Alzheimer's disease at 1.7 years, compared with 25 percent of those who took vitamin E or the placebo. At 2.2 years, 14 percent of the donepezil group had developed Alzheimer's, compared with 29 percent of the vitamin E and placebo groups. 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," Lu said.
Donepezil is not approved by the Food and Drug Administration for use in treating mild cognitive impairment. The drug 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, an Alzheimer's Disease Cooperative Study grant, the Alzheimer's Disease Research Center, Jim Easton and the Sidell Kagan Foundation.
Other authors included J.L. Cummings, E. Teng and K. Tingus of UCLA; S.D. Edland of the University of California, San Diego; and R.C. Petersen of the Mayo Clinic College of Medicine.
Dr. Petersen has served as a paid consultant to GE Healthcare and has served on safety monitoring committees for Elan Pharmaceuticals and Wyeth; Dr. Cummings has served as a paid consultant to Abbott, Acadia, Accera, ADAMAS, Astellas, Avanir, Bristol-Myers Squibb, CoMentis, Eisai, En-Vivo, Forest, Janssen, Lilly, Lundbeck, Medivation, Merck, Merz, Myriad, Neuren, Novartis, Pfizer, Prana, Schering Plough, Sonexa, Takeda, Toyama and Wyeth.
The Mary S. Easton Center for Alzheimer's Disease Research is part of the UCLA Department of Neurology, which encompasses more than a dozen research, clinical and teaching programs. These programs cover brain mapping and neuroimaging, movement disorders, Alzheimer's disease and other dementias, multiple sclerosis, neurogenetics, nerve and muscle disorders, epilepsy, neuro-oncology, neurotology, neuropsychology, headaches and migraines, neurorehabilitation, and neurovascular disorders. The department has ranked No. 1 among its peers nationwide in National Institutes of Health funding for the last seven years (2002-2008).
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