A new study reveals that depression is associated with the later development of Alzheimer’s disease and vascular dementia — a condition caused by blocked or reduced blood flow to the brain, depriving brain cells of oxygen and nutrients.
The report in the British Journal of Psychiatry is an analysis of 23 prior studies that followed nearly 50,000 older adults over a median of five years. The researchers found that depressed older adults (over age 50) were more than twice as likely to develop vascular dementia and 65 percent more likely to develop Alzheimer’s disease than those who weren’t depressed.
“We can’t say that late-life depression causes dementia, but we can say it likely contributes to it,” said co-author Meryl Butters, Ph.D., an associate professor of psychiatry at the University of Pittsburgh School of Medicine.
“We think depression is toxic to the brain, and if you’re walking around with some mild brain damage, it will add to the degenerative process.”
The findings reveal that 36 of every 50 older adults with late-life depression may go on to develop vascular dementia, while 31 of every 50 seniors with a history of depression may eventually develop Alzheimer’s.
Previous studies have shown that a history of depression is linked to double the risk of developing Alzheimer’s disease. But this is the first study to demonstrate an even stronger association with vascular dementia.
What could be behind the relationship between depression and dementia? One theory is that people who are depressed produce high levels of the hormone cortisol, which in turn has a negative effect on the hippocampus — a region of the brain responsible for new learning and short-term memory.
“We know that people who are depressed have elevated levels of cortisol, a hormone related to the stress response, and a smaller hippocampus, a brain structure critically important for memory,” said Dr. Raymond Ownby, chair of psychiatry at Nova Southeastern University’s College of Osteopathic Medicine, who studies the possible links between depression and dementia.
Other evidence suggests that depression contributes to chronic inflammation that damages blood vessels and hinders blood flow in the brain, leading to the deterioration of neural networks.
Some experts also believe that depression may share genetic underpinnings with dementia, be an early sign of dementia, or serve as an emotional reaction to impaired thinking and a worsening memory.
Whatever the reason, the implications for older adults are clear. “If someone in later life develops depression, they should get early, aggressive treatment, and if they do so and recover, they should try to prevent recurrence,” Butters said.
Source: British Journal of Psychiatry