Alzheimer's was four times more likely in people with depression before aged 60, Dutch and U.S. researchers reported in Neurology and Archives of General Psychiatry.
The Dutch researchers from the Erasmus University Medical Center in Rotterdam studied 486 people over an average of six years. Just 33 people developed Alzheimer's. More research is needed to fully understand the link between Alzheimer's and depression, researchers believe.
Scientists believe that depression leads to the loss of cells in two areas of the brain, the hippocampus and the amygdale. The non-functioning of these two areas contributes to Alzheimer's disease.
Alzheimer's destroys brain cells, causing problems with memory, thinking and behavior severe enough to affect work, lifelong hobbies or social life. Alzheimer's gets worse over time, and it is fatal.
A second study by Rush University in the U.S. followed more than 900 members of the Catholic clergy. Nearly190 of them developed Alzheimer's for up to 13 years of follow up. Those with more signs of depression at the start of the study were more likely to develop Alzheimer's.
The researchers conclude in their findings that "depression was a risk factor for Alzheimer's disease - rather than a subtle early sign of its underlying pathology."
As many as 5 million Americans are living with Alzheimer's disease. Today it is the seventh-leading cause of death in the United States.
