"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," lead researcher Dr. Monique M.B. Breteler, from the Erasmus University Medical Center in Rotterdam, the Netherlands, said in a statement. "We'll need to do more studies to understand the relationship between depression and dementia."
In the study, Breteler and her colleagues collected data on 486 people, aged 60 to 90, who did not have dementia. Among these individuals, 134 had had at least one episode of depression.
During an average six years of follow-up, 33 people developed Alzheimer's disease. The researchers found that those who had had an episode of depression were 2.5 times more likely to develop Alzheimer's compared with people who had never had depression. For people whose depression occurred before they were 60, the risk for developing Alzheimer's was fourfold greater than people who had never had depression, the researchers reported.
One goal of Breteler's research was to determine if depression causes changes in the brain that increase the risk of Alzheimer's disease, as had been suspected by other scientists.
Researchers have proposed that depression leads to a loss of cells in the areas of the brain called the hippocampus and the amygdala, thereby increasing the risk for Alzheimer's. However, Breteler's group didn't find any difference in the size of those areas of the brain in people with or without depression.
In addition, Breteler's team found that people who had symptoms of depression at the start of the study were no more likely to develop Alzheimer's than those who did not have the symptoms.
Even though the study found a connection between depression and Alzhei
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