April 8, 2008

Depression May Increase Risk of Developing Alzheimer’s

People who have reported symptoms of depression in the past are more susceptible to developing Alzheimer's disease, according to two recent studies.

One U.S. study, which appears in the journal Archives of General Psychiatry, evaluated 917 older Catholic nuns, priests, and monks who had not reported dementia before the study began.

The participants completed annual clinical evaluations including administration of the 10-item Center for Epidemiologic Studies Depression Scale and clinical classification of mild cognitive impairment and Alzheimer's disease.

Researchers at Rush University noted that 190 of participants developed Alzheimer's disease, adding that those who had more symptoms of depression at the onset of the study were more likely to develop Alzheimer's.

Dr. Robert Wilson, a neuropsychologist at Rush University Medical Center in Chicago who led one study, said that he and his colleagues believe that damage to the brain's limbic system is the primary target of both depression and Alzheimer's disease.

"Our thinking is that depression somehow causes damage to part of the brain called the limbic system, and this is the part of the brain that Alzheimer's disease preferentially attacks," Wilson said.

The limbic system includes the hippocampus and amygdala, which play key roles in emotions and memory.

"In terms of depressive symptoms, those are fairly consistent from year to year as people have a chronic tendency to be depressed or not be depressed -- it's not just something that randomly varied from year to year," Wilson said.

In the smaller Dutch study, researchers from the Erasmus University Medical Center in Rotterdam studied a group of 486 people over six years. They noted that only 33 people developed Alzheimer's.

"We don't know yet whether depression contributes to the development of Alzheimer's disease, or whether another unknown factor causes both depression and dementia," said lead researcher Dr Monique Breteler.

The Dutch study found no difference in the size of the hippocampus and the amygdala in people with depression and people who had never developed the condition.

Rebecca Wood, of the Alzheimer's Research Trust said that the new results were important and noteworthy for future research.

"Identifying people at higher risk could lead to ways to reduce the number of people who develop dementia, help researchers to understand more about dementia and create new avenues of research."


On the Net:

Archives of General Psychiatry

Alzheimer's Association