People with depression are more likely to later develop Alzheimer's disease, according to two studies published on Monday, and one team said that chronic stress may damage their brains.
"What we think it suggests is that depression truly is a risk factor for Alzheimer's disease, and not simply a sign that the disease is developing," Dr. Robert Wilson, a neuropsychologist at Rush University Medical Center in Chicago who led one study, said in a telephone interview.
Some researchers have assumed that Alzheimer's causes depression, so Wilson's team tracked 917 retired Catholic priests and nuns, 190 of whom developed Alzheimer's disease. Those with more symptoms of depression at the beginning of the study were more likely to develop Alzheimer's disease.
But Wilson's group did not find a sudden onset or worsening of depression in the few years before symptoms of the brain disease took hold.
"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.
The subjects in the study, which appeared in the Archives of General Psychiatry, were asked about depressive symptoms and not about specific episodes.
"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.
