Is Depression a Risk Factor with Alzheimer’s?

Published on: January 27, 2012

by Carrie Hill, PhD for Dementia & Alzheimers

Depression and Alzheimer’s disease share a complex relationship. Depression — a mental disorder caused by chemical imbalances in the brain — can include symptoms that look like Alzheimer’s, such as concentration problems, memory impairment, and difficulty making decisions. When depression looks like Alzheimer’s disease or another dementia, it’s often referred to as pseudodementia. It’s treatable, but relapse is a significant concern.

Depression and Alzheimer’s disease can also occur together, where each disorder requires treatment that doesn’t interfere with the treatment of the other condition. This is another complex diagnostic and treatment situation.

Researchers are now looking at a third way that depression and Alzheimer’s may be related: They want to know whether depression is a risk factor for the disease. Two studies shed some interesting light on this question.

The first study, which appeared in the April 2008 issue of Archives of General Psychiatry, found a correlation between depression and Alzheimer’s disease; however, they also found that depressive symptoms did not worsen immediately before a diagnosis of Alzheimer’s was made. If depression increased at the same rate of cognitive decline (which usually precedes diagnosis), they would have wondered whether depression was a consequence of Alzheimer’s, rather than a risk factor. Instead, the researchers now think that depression may change brain chemistry in such a way that the brain becomes more susceptible to Alzheimer’s disease.

The second study, which appeared in the April 8, 2008 issue of Neurology, investigated whether a history of depression was associated with the later development of Alzheimer’s disease. The researchers found that people who have had depression are almost 2.5 times more likely to develop Alzheimer’s than those who haven’t had depression. Furthermore, those who experienced depression before the age of 60 were almost four times more likely to develop Alzheimer’s disease.

The researchers in the second study were cautious about assuming that depression directly increased risk for Alzheimer’s disease. While the evidence might point to that conclusion, they said that there could be a third, unknown factor that increases risk for both depression and Alzheimer’s in some individuals by affecting brain chemistry or structure in ways that are associated with both conditions.

Obviously, more research needs to be conducted to further clarify the relationship between depression and Alzheimer’s disease. These studies certainly indicate that depression earlier in life may be a risk factor for the later development of Alzheimer’s, but I’m looking forward to future studies to more clearly illuminate this connection.

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