Depression is commonly reported in people with Alzheimer's disease and its precursor, mild cognitive impairment, with several studies suggesting having a history of major depression may nearly double your risk of developing dementia later in life. However, it has been unclear if depression is a symptom of the disease or a potential cause of the disease.
To study the relationship between Alzheimer's and depression, researchers at Rush University Medical Center tracked symptoms of depression during the transition from no cognitive impairment to dementia and found that depressive symptoms show little change during the development and progression of Alzheimer's disease. The study will be published in the July 6 issue of Neurology, the medical journal of the American Academy of Neurology.
"Our study suggests that depression is truly a risk factor for Alzheimer's disease," said lead author Robert S. Wilson, PhD, senior neuropsychologist, Rush Alzheimer's Disease Center, and a professor in the Department of Behavioral Sciences at Rush. "If depression was an early sign of the disease, we would expect to see it increase prior to diagnosis and as the disease progresses. Our study found very little change."
"Depression should not be viewed as an inevitable part of Alzheimer's disease. If a patient with Alzheimer's has depression, the depression should be treated," said Wilson.
The study involved participants in the Chicago Health and Aging Project, a longitudinal study of risk factors for Alzheimer's disease involving a population of older adults on Chicago's south side. At three year intervals, the entire population completed a brief self-report measure of depressive symptoms and clinical evaluations for Alzheimer's disease.
Initial analyses focused on a group of 357 individuals who developed Alzheimer's disease during the course of the study. The study found a barely perceptible increase in depressive symptoms, a rate of 0.04 symptoms per year, during six to seven years of observation before the diagnosis of Alzheimer's disease and no change during two to three years of observation after the diagnosis.
Because dementia may reduce the accuracy of self-report, in a subgroup of 340 participants, researchers conducted additional analyses of change in depressive symptoms by interviewing family, friends and other who were close to the study participants. Neither Alzheimer's disease nor its precursor, mild cognitive impairment, was associated with change in depressive symptoms during a mean of three years of observation.
The results were consistent across all demographics. There was no evidence that sex, age, education or race modified the trajectory of depressive symptoms before or after Alzheimer's disease was diagnosed.
"Here is this terrible disease that robs people of who they are and their ability to function and yet it doesn't make them depressed," said Wilson. "Alzheimer's may disrupt the ability to have prolonged bouts of negative emotions, in much the same way it disrupts many other activities."
The study authors suggest additional studies of patients with Alzheimer's disease for longer periods to determine if depressive symptoms may eventually decrease as the disease becomes more severe.
In addition, researchers at Rush continue to look at why depression increases the risk of Alzheimer's disease.
The study was supported by funding from the National Institutes of Health (NIH)/ National Institute on Aging (NIA). Co-authors include G.M. Hoganson, BS; K.B. Rajan, PhD; L.L. Barnes, PhD; C.F. Mendes de Leon, PhD; and D.A. Evans, MD.
- R.S. Wilson, G.M. Hoganson, K.B. Rajan, L.L. Barnes, C.F. Mendes de Leon, and D.A. Evans. Temporal course of depressive symptoms during the development of Alzheimer disease. Neurology, 2010; 75: 21-26 [link]
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