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Published on: November 21, 2015
Although scientists have known for a long time about an association between depression and dementia, the exact nature of that complex relationship remains unclear. People who are depressed often, but not always, go on to develop dementia and many people with dementia are depressed. (In fact, according to the Alzheimer’s Association, as many as 40 percent of people
with Alzheimer’s disease also experience depression.)
Research has revealed some information about why depression and dementia often occur together but the results have been inconsistent, and much remains to be learned. So far, there are three main theories about the nature of the
Let’s examine each of these theories in more detail.
1. Depression is a potential risk factor for dementia
Research published in Gerontology in 2000 reviewed existing epidemiological evidence and concluded that “there is sufficient evidence to take seriously the possibility that depression is a risk factor for dementia and cognitive decline.”1 In the decade and a half since then, new studies continue to point to the possibility that depression is a risk factor for dementia. For example:
A meta-analysis of 23 previous studies that followed almost 50,000 older adults over a median lifespan of five years was published in 2013 in the British Journal of Psychiatry. The report concluded that late-life
depression likely contributes to dementia, although it can’t be confirmed, based on the findings, that late-life depression causes dementia. The researchers think that depression is toxic to the brain.
A study published in Neurology in July 2014 reported that depression is a risk factor for dementia; furthermore, it found that the more symptoms of depression one suffers, the more rapidly thinking and memory skills decline. The study authors emphasized that while they did find an association between depression and dementia, their findings did not prove a cause-and-effect relationship.
2. Depression is a potential early sign of dementia
A study published in the March 2013 issue of JAMA Neurology suggests that depression in older adults may be an early symptom of dementia, rather than a separate risk factor for it. The research looked at 2,160 New Yorkers aged 65+ and found that late-life depression accompanies cognitive decline but does not precede it. The results suggest that depression develops as one experiences a decline from normal cognition to dementia. Some experts have hypothesized that depression occurs as an emotional reaction to the challenging impacts of dementia such as impaired thinking and unreliable memory.
3. Depression and dementia might share common cause(s)
Just because depression and dementia are often both present simultaneously in a patient does not mean that the two conditions are directly related. It’s possible that a third, separate factor increases risk for both depression and dementia by affecting brain chemistry or structure in ways found in both conditions. One theory is that vascular disease – which impairs blood circulation in the body – could be that third factor. In particular, cerebrovascular disease might be the key. Cerebrovascular disease is a group of conditions that impede or block the flow of blood specifically to the brain. It is easy to imagine how impaired circulation of blood to the brain could cause changes that lead to numerous negative side effects including dementia and depression.
The Effect of Life Stage
The depression-dementia relationship is perhaps even more complex than these three theories would suggest. A study published in the May 2012 issue of Archives of General Psychiatry looked at the possibility that the nature of the relationship varies based on the type of dementia and when in one’s lifetime depressive symptoms are experienced. The results suggest that depression occurring for the first time in late-life may be an early symptom of dementia, particularly Alzheimer’s disease, while chronic depression (occurring in mid and late-life) may be a reflection of long-term changes in blood flow to the brain that increase risk of vascular dementia.
Clearly, more research is needed, particularly long-term studies are necessary in order to further clarify the relationship between depression and dementia. In the meantime, there is action you can take to be proactive about your mental and cognitive health.
Taking Action for Your Health
Diagnosis Since depression and dementia share such a complex, yet not entirely understood, relationship, it’s no surprise that diagnosing an older person who is showing signs of cognitive decline and/or depressive symptoms is a complex undertaking. Similar symptoms can make it difficult to tell the difference between depression and dementia. Examples of such symptoms include apathy, loss of interest in hobbies, social withdrawal, concentration problems and memory impairment.
Just as there is no single test to diagnose dementia, there is also no single test to detect depression. However, the National Institute of Mental Health in the United States has established a formal set of guidelines for diagnosing depression in someone known to have Alzheimer’s disease. The criteria for these tests are similar to general diagnostic standards for major depression but vary in that they reduce the emphasis on verbal expression and take into consideration irritability and social isolation.
Assessing a dementia patient for possible depression requires a thorough evaluation by a medical professional and may best be performed by a geriatric psychiatrist who specializes in recognizing and treating depression in older adults.
Treating Early Depression on its Own:
As the exact nature of the relationship between depression and dementia remains a mystery, it is not clear whether treating depression could help decrease the risk of developing dementia. Research does raise hope, however, that adequate treatment of midlife depression may reduce later dementia risk, particularly vascular dementia. For this reason, it makes sense to pursue treatment of depressive symptoms when they appear in order to reduce the risk of any other health risks such as dementia, as well as to improve quality of life and relieve suffering.
Treating Dementia Patients Who Are Depressed: According to the Alzheimer’s Association, the most common treatment for depression in Alzheimer’s patients involves “a combination of medicine, counselling and a gradual reconnection to activities and people that bring happiness.” They warn that simply telling a depressed Alzheimer’s patient to “cheer up” or “snap out of it” is not helpful; these individuals usually need a lot of support, reassurance and professional help to address depressive symptoms.
Prevention In addition to identifying and treating depressive symptoms, healthy lifestyle habits are also important for reducing the risk of both depression and dementia. Healthy choices that are known to help with treatment of depression, including good nutrition, regular exercise and participating in engaging social activities – are also good for staving off dementia. It turns out that the old adage is true: what’s good for your mental health is good for your brain, too.
Depression is Different in Women and Men
Adding to the complexity of the depression-dementia link is the reality that women and men differ when it comes to depression. For starters, women are more likely to experience depression with about twice the risk as men. Other differences include:
(Incidentally, women and men differ when it comes to dementia, too. That’s why Women’s Brain Health Initiative was founded – to raise awareness of the differences and address the lack of research focused on women’s brains.)
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