Although it is not clear that people with depression are at increased risk for Alzheimer's disease, new data suggest depressive symptoms do not increase in the years before diagnosis of dementia, according to an article in the April issue of Archives of General Psychiatry.

If confirmed, the finding suggests that depression is not a consequence of developing Alzheimer's disease but may instead be a risk factor for it. Previous studies had found higher levels of depressive symptoms among patients with Alzheimer's disease and its precursor, mild cognitive impairment, according to background information in the article.

Robert S. Wilson, PhD, of Rush University Medical Center, Chicago, and colleagues studied 917 older Catholic nuns, priests and monks who did not have dementia at baseline in 1994. Participants had a yearly clinical evaluation that included a neurological examination, cognitive testing and classification of Alzheimer's disease or mild cognitive impairment. They also completed a 10-item scale assessing 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 wrote. "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 wrote. "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."