Although individuals with depression may be more likely to develop Alzheimer's disease, symptoms of depression do not appear to increase in the years before a diagnosis is made, according to a report in the April issue of Archives of General Psychiatry, one of the JAMA/Archives journals. This suggests that depression is not a consequence of developing Alzheimer's disease but may instead be a risk factor for dementia.
Previous studies have found higher levels of depressive symptoms (such as feeling sad) among patients with Alzheimer's disease and its precursor, mild cognitive impairment, according to background information in the article. "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 this were the case, symptoms of depression would likely increase during the early stages of Alzheimer's disease.
Robert S. Wilson, Ph.D., of Rush University Medical Center, Chicago, and colleagues studied 917 older Catholic nuns, priests and monks who did not have dementia beginning in 1994. Participants had a yearly clinical evaluation that included a neurological examination, cognitive (thinking, learning and memory) testing and classification of Alzheimer's disease or mild cognitive impairment. They also completed a 10-item scale assessing their symptoms of depression.
At the beginning of the study, 53.6 percent of participants reported no symptoms of depression, 23.9 percent reported one symptom, 9.7 percent reported two, 6.1 percent reported three and 6.8 percent reported four or more. During follow-up, 190 individuals developed Alzheimer's disease. Those with more symptoms of depression at the beginning of the study were more likely to develop Alzheimer's disease.
However, "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," the authors write. "Among those without cognitive impairment at baseline, depressive symptoms did not increase in those who subsequently developed mild cognitive impairment."
Symptoms of depression may be associated with changes in the brain that reduce its resistance to dementia, the authors write. "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."
(Arch Gen Psychiatry. 2008;65:439-446. Available pre-embargo to the media at www.jamamedia.org.)
Editor's Note: This study was supported by grants from the National Institute on Aging. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.