A history of depression, particularly at an early age, is associated with an almost four-fold increase in the risk of developing Alzheimer’s disease according to a recent study published in the April 08 edition of the journal Neurology.
The researchers, based in Rotterdam, The Netherlands, analyzed 486 people between the ages of 60 or 90 who were free of dementia at the beginning of the study. The participants were followed for a period of six years during which 33 people (6.6%) developed Alzheimer’s disease.
Of the participants, 134 (27%) indicated that they had a history of depression, with 88 of these individuals reporting depression before the age of 60 and 46 individuals indicating depression had began after the age of 60.
After controlling for other variables, the researchers reported that individuals with a history of depression before the age of 60 were 3.76 times more likely to develop Alzheimer’s disease compared to those with no history of depression. Those who developing depression after the age of 60 were 2.34 times more likely to develop Alzheimer’s disease than those with no history of depression.
The researchers believe that depression may damage the limbic system, which is a part of the brain housing the hippocampus and amygdala which play a role in controlling emotions, long term memory, and behavior.
In a previous study, published in the journal Archives of General Psychiatry, researchers had found that the brains of Alzheimer’s disease patients who had a history of depression had more tangles and plaques in the hippocampus than Alzheimer’s disease sufferers who did not have a history of depression.
In that study however, brain scans of the subjects did not reveal a link between depression and damage to either the hippocampus or the amygdala.
Cortisol levels are raised in depressed individuals and another possible explanation for the link between depression and Alzheimer’s disease is that high cortisol levels, which are associated with inflammatory activity in the body, may cause oxidative stress leading to greater free radical production and neuron cell damage in the brain.
Another possible explanation for the link is that early changes in the brain caused by Alzheimer’s disease may manifest themselves as depression. It is therefore possible that depression may be an early warning symptom of changes in the brain caused by processes associated with early Alzheimer’s disease such as beta-amyloid plaque development.
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