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Depression as a Risk Factor for Dementia

Researchers say there is a relationship between depression and dementia. A new study finds the clearest evidence yet of a possible link.

Researchers have long theorized that depression as people age may be linked to dementia later in life. Now a new study reveals that it may indeed be a risk factor.

“In this study we wanted to find out if the reason depression predicts dementia is because it is really an early sign of the disease,” says Robert S. Wilson, PhD, lead researcher on the study and a professor of neuropsychology at Rush University in Chicago. “This has been a persistent question throughout the research. We know that it takes years for dementia to develop, and sometimes these subtle changes in behavior that predict later disease are really early signs.”

For the study, published in the journal Neurology in July 2014, Wilson and his colleagues looked at more than 1,700 older people who did not have dementia or depression. They screened the participants for both depression and dementia symptoms once a year for about eight years, and they also examined autopsy reports for those who died during the study, looking for signs of dementia and cognitive decline, Wilson says.

During the study period, 52 percent of the participants developed mild cognitive impairment, and 18 percent developed dementia. Those who developed dementia had a higher level of depression symptoms before their dementia set in than the others.

Theories on the Depression-Dementia Link

Scientists are still learning about the relationship between depression and dementia, and Wilson's study builds on previous research about the connection between the two conditions. According to the Alzheimer’s Association, up to 40 percent of people with Alzheimer’s disease also have depression, but experts haven’t uncovered the reasons why depression and dementia occur together. However, a few top theories have persisted:

  • “One theory on the relationship between depression and dementia is that depression is an early sign or symptom of dementia,” says Ashley Gorman, PhD, a clinical neuropsychologist with the Morris Psychological Group in Parsippany, New Jersey. “In this theory, the budding dementia is actually causing the depression.”

  • Another theory holds that depression may directly damage the brain, leading to dementia. “Simply put, chronic stress and/or depression may result in the release of cortisol,” Gorman says. Over time, this stress hormone can harm the brain, she says.

  • A third theory points to reduced brain volume. “Depression may alter brain volumes, which puts a person at increased risk of earlier symptoms of dementia,” says Paul Schulz, MD, an associate professor of neurology at the University of Texas Medical School at Houston.

Treating Depression Before Dementia

“One important implication of our study is that people with symptoms of depression should pursue treatment even if their symptoms aren’t disabling,” Wilson says.

Symptoms of depression can include problems with memory, concentration, and decision making. Treatment for depression may include medications or behavioral therapy. The goal, Dr. Schulz says, is to shorten the depression in hopes of reducing the risk for dementia.

In addition, as depression gets better with treatment, so do memory symptoms, according to the Alzheimer’s Association. If you continue to have memory symptoms like forgetfulness as your depression improves, talk with your physician. Also consider seeing a neuropsychologist, who can identify signs of dementia.

Healthy habits are also important when it comes to staving off both depression and dementia. “There is no substitute for daily exercise and good nutrition,” says Laura Boxley, PhD, an assistant professor of clinical psychiatry at The Ohio State University in Columbus.

“Recent studies have found regular exercise decreases your risk for dementia," she says. "Exercise is also a great treatment for depression. Whether it’s running, walking, swimming, or gardening, I tell patients to do at least 30 minutes of moderate exercise five days a week,” she says.

Gorman agrees, adding that having an active social life and participating in mentally challenging and engaging activities are critical as well. “Anything good for your heart is good for your brain,” she says.

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