Mood and behavioral changes may precede memory problems in people with the disease.
Alzheimer’s accounts for 60 to 80 percent of cases of dementia.
Alzheimer’s disease is the most common form of dementia. Many people with AD have depression.
New research suggests depressive symptoms may appear before cognition issues for some people who develop AD.
Depression also becomes more common with age, the study found.
For people who develop Alzheimer’s disease (AD), depressive symptoms and other “noncognitive” changes may occur before any of the hallmark memory and thinking problems associated with the disease, according to a new study published in the journal Neurology.
Researchers analyzed the performance of approximately 2,400 Americans ages 50 and older on various assessments of psychological health, behavior, and the ability to perform daily activities.
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All of the participants were cognitively normal (ie, no signs of dementia) in the beginning, but over the course of the nearly 8-year-long study, about half of them developed dementia. The researchers found that those who developed dementia were more likely to experience mood and behavior changes before any other symptoms.
Specifically, within the first four years of the study, 30 percent of the participants who would later go on to develop dementia already showed depressive symptoms, such as significantly decreased energy, apathy, and increased preference for staying home. By comparison, only about 15 percent of people who didn’t develop dementia showed depressive symptoms.
Importantly, the study didn’t look at clinical depression, only depressive symptoms, researchers say, adding that it’s possible to have depressive symptoms without having clinical depression.
“And we want to make sure people understand that if they’re having depressive symptoms, it doesn’t necessarily mean they’re going to get Alzheimer’s disease,” says study senior author Catherine Roe, PhD, a neurologist at the Washington University School of Medicine in St. Louis.
However, Dr. Roe says, the study shows that “if you are going to eventually get Alzheimer’s disease, it’s likely that depressive symptoms are going to happen sooner than any memory or cognitive symptoms.”
What Is Dementia and Alzheimer’s Disease?
Dementia is not a specific disease, but rather a general term to describe a decline in cognitive or mental ability — including memory and other thinking skills — that’s severe enough to interfere with daily life.
Alzheimer’s disease is a progressive brain disease and the most common cause of dementia, accounting for 60 to 80 percent of cases, according to the Alzheimer’s Association.
It’s unclear what causes AD, but research suggests the protein beta-amyloid plays an important role in the disease, considering that beta-amyloid plaques are found on the brains of all patients with AD.
These plaques, however, can start forming decades before any AD symptoms develop, and having the plaques doesn’t mean a person will definitely get AD.
Aside from AD, several other types of dementia exist, including vascular dementia, which is caused by stroke, and Lewy body dementia, which is caused by the abnormal clumping of another protein in the brain.
The Link Between Depression and AD
Depression is very common among people with dementia and AD. In fact, up to 40 percent of people with AD may suffer from severe depression, according to the Alzheimer’s Association.
But the link between depression and dementia is not the same for everybody, and there are actually three general groups of people who suffer from both issues, says Paul Schulz, MD, a neurologist at the University of Texas Medical School at Houston, who wasn’t involved in the study.
“The first group consists of people who have had depression lifelong, or on and off since they were young,” Dr. Schulz says. “We know epidemiologically that they are at a higher risk of getting dementia.”
For this group, changes in the brain caused by depression may be what puts them at risk for dementia. “There are some areas of the brain that we know are, on average, a little smaller in people with depression than other folks,” Schulz says.
The second group of people develops depression after memory loss and other cognitive symptoms of dementia set in. These people, Schulz explains, may get depression as a reaction to the changes in their life.
The third group of people is directly addressed in Roe’s research.
“This group is one where they develop depression or anxiety or a change in behavior, like being short-fused or agitated or aggressive, and then later on develop cognitive symptoms,” Schulz says. “But not decades later. It’s in the next eight years or so that a certain percentage of them will develop dementia.”
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It’s not uncommon for clinicians to encounter these types of people, Schulz says. But, until now, research hasn’t formally identified them because they are difficult to study — people with depression don’t often do well on cognitive tests, making it hard to tell if they have or are developing dementia. This fact makes this new study all the more interesting and important, he says.
Explaining the depression-dementia link in this group, Schulz says that dementia is basically “changes in the brain.” These changes are generally reflected in memory loss, getting lost, language changes, and other things, so clinicians say they are part of a “cognitive issue.”
“But everything we do as humans comes from the brain, so it all has a cognitive component,” Schulz says. “So if the mood part of the brain was changed before anything else [as dementia develops], you could actually have depression as the presenting symptom of dementia.”
Why These Findings Matter
For Schulz, there are two important takeaways from the study.
For one thing, it suggests that depression gets more common as we get older, he says. “Secondly, dementia is more common among those with [depressive symptoms] than without.”
But Schulz and Roe agree that the study doesn’t suggest people over 50 years old with depression should become alarmed about dementia. “There were lots of people with depressive symptoms in the study who didn’t go on to develop AD,” Roe says.
Rather, the study is important for healthcare professionals.
That is, if an older patient comes in with depression for the first time in his or her life, especially depression that appears more difficult-to-treat than normal, the clinician or psychiatrist should make sure to ask their patient (or their patent’s loved ones) if there have also been any recent problems with memory, thinking, and other cognitive functions.
“And I think that you should always make sure to tell your doctor about whatever symptoms you are having,” Roe says.
In the future, studies could test if there’s an association between beta-amyloid plaque formation and depressive symptoms, Schulz says, adding that this could not only help scientists better understand the connection between depression and dementia, but also potentially better predict who will get AD.