While there is a correlation between individuals with depression and the development of Alzheimer's disease, it appears that the symptoms of depression do not increase in the years before an Alzheimer's diagnosis, according to a report released on April 7, 2008 in the JAMA/Archives journal Archives of General Psychiatry.

Previous studies have shown that patients with Alzheimer's or its precursor, mild cognitive impairment, have higher levels of depressive symptoms, which include feeling sad or a diminished ability to feel pleasure. According to the article, this association's causality is not clear. "The basis of this association is uncertain, however," the authors write. "A leading hypothesis is that depressive symptoms do not constitute a true risk factor but rather a consequence of the disease." If hypothesis was true, the symptoms of depression would coincide with the symptoms of Alzheimer's, and thus increase in the early stages of the disease.

To investigate the cause of the correlation, Robert S. Wilson, Ph.D., of Rush University Medical Center, Chicago, and colleagues examined older Catholic nuns, priests, and monks who did not have dementia. A total 917 patients were examined beginning in 1994. They were evaluated early by: neurological examination; cognitive exam investigating thinking, learning, and memory; classification for Alzheimer's disease or mild cognitive impairment; and a ten item scale to access their symptoms of depression.

When the study began, 53.6% of participants presented no symptoms of depression, 23.9% reported one symptom, 9.7% reported two, 6.1% reported three, and 6.8% reported more. In the later examination, 20.7% of the individuals (190) developed the disease. If someone displayed symptoms of depression at the beginning of the study, he was more likely to develop Alzheimer's disease by the end.

However, the levels of symptoms did not change at the same time: "those who developed Alzheimer's disease showed no increase in depressive symptoms before the diagnosis was made, and this finding was not modified by age, sex, education, memory complaints, vascular burden or personality," say the authors. "Among those without cognitive impairment at baseline, depressive symptoms did not increase in those who subsequently developed mild cognitive impairment." This indicates that depression is not a consequence of Alzheimer's, but rather a risk factor for the development of dementia.

The authors offer the explanation that depression may intrinsically change the brain to make it less resistant to dementia. They add: "Understanding the mechanisms linking depressive symptoms with dementia could suggest novel approaches to delaying dementia onset because animal research suggests diverse means by which the adverse effects of chronic stress may be modified."

Change in Depressive Symptoms During the Prodromal Phase of Alzheimer Disease
Robert S. Wilson, PhD; Steven E. Arnold, MD; Todd L. Beck, MS; Julia L. Bienias, ScD; David A. Bennett, MD
Arch Gen Psychiatry. 2008;65(4):439-445.
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Anna Sophia McKenney