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Depression and Alzheimer's Linked
April 7, 2008 -- A history of depression, especially if it occurs early in life, boosts your risk of getting Alzheimer's disease, according to a new study.
But depression does not seem to increase during the early stages of Alzheimer's disease, according to another new study, refuting the idea that the Alzheimer's causes the depression, as some claim.
Together, the two studies contribute some answers to the ongoing debate about depression and Alzheimer's disease -- and whether depression triggers the Alzheimer's disease, the Alzheimer's disease triggers the depression, or yet another risk factor leads to both. Up to 50% of Alzheimer's patients also report depression.
The new research strengthens advice to take depression seriously and get treatment, says Gary Kennedy, MD, director of geriatric psychiatry at Montefiore Medical Center, New York, N.Y. "You want to get over it as quickly and completely as possible," says Kennedy, who reviewed the studies for WebMD.
Depression and Alzheimer's: Role of History Study
To look at the link between depression and Alzheimer's disease, researchers from Erasmus Medical Center in the Netherlands assessed 503 men and women, aged 60 to 90 at the study start and free of dementia. All were participants in the Rotterdam Scan Study, an ongoing research effort to look at chronic diseases in the elderly.
Participants reported any history of depression and noted if it occurred before or after age 60. They also reported any symptoms of depression at the study start.
Researchers also performed three-dimensional MRI scans to look at the volume of two brain areas -- the hippocampus and the amygdala, two areas that some experts say shrink in those with depression. They wanted to see if they could document that suspected association.
After a six-year follow-up, 33 people developed dementia; 134 of the participants had a history of depression (88 early onset, 46 late).
If the depression occurred before age 60, the researchers report, the risk of getting Alzheimer's disease later was nearly four times as great as for those who did not have a history of depression. If the depression occurred after age 60, the risk was about 2.5 times greater than the risk for the depression-free.
Depression at the start of the study was not associated with an increased risk for Alzheimer's disease.
The researchers then looked at who had depression and who did not, and compared the sizes of their hippocampus and amygdala. They found no association between the sizes of those brain areas and depression, refuting the idea that the shrinkage in the brain contributes to the Alzheimer's disease.
"Our findings definitely do not support the notion that depression leads to loss of hippocampus and amygdala cells which then leads to Alzheimer's," says Monique M.B. Breteler, MD, PhD, professor of neuroepidemiology at Erasmus University and the study's lead author, in an email interview.
Yet a third factor, she says, could be causing both depression and Alzheimer's, and more research is needed to find out exactly what.
The study is published in Neurology.
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