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. 

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 depressive 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 dementias, 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.” 

About Alzheimer's Disease 

Alzheimer’s disease (AD) is a slowly progressive disease of the brain that is characterized by impairment of memory and eventually by disturbances in reasoning, planning, language, and perception. Alzheimer’s disease is the most common cause of dementia, which afflicts 24 million people worldwide. Alzheimer's disease is not a normal part of aging and is not something that inevitably happens in later life. It is rarely seen before the age of 65. The likelihood of having Alzheimer’s disease increases substantially after the age of 70 and may affect around 50% of persons over the age of 85.

About Dementia 

Dementia is a progressive brain dysfunction (in Latin 'dementia' means irrationality), which results in a restriction of daily activities and in most cases leads in the long term to the need for care. Many diseases can result in dementia, the most common one being Alzheimer's disease .

The probability of suffering from dementia increases with advancing age. Dementia predominantly occurs in the second half of our life, often after the age of 65. The frequency of dementia increases with rising age from less than 2 % for the 65-69-year-olds, to 5 % for the 75-79 year-olds and to more than 20 % for the 85-89 year-olds. Every third person over 90 years of age suffers from moderate or severe dementia (Bickel, Psycho 1996, 4-8). About half of those affected by dementia suffer from Alzheimer's disease.