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Depression Increases the Risk of Alzheimer’s Disease

Depressed Man - Alzheimer's

January 29, 2020

Being depressed increases the risk of developing Alzheimer’s disease and other forms of dementia, a new study reports. The study found that men and women with a diagnosis of depression were at increased risk of getting a dementia diagnosis, and the risk persisted even more than 20 years later.

The study, in PLOS Medicine, consisted of two parts. In one, researchers in Sweden tracked nearly 120,000 men and women over 50 who had been diagnosed with depression, comparing them with peers who were not depressed. They followed them for up to 35 years, with an average follow-up time of more than 10 years.

They found that Alzheimer’s disease or other forms of dementia developed in 5.7 percent of those who had depression, compared to just 2.6 percent of those who were not depressed. Dementia was particularly prevalent in the first year after a depression diagnosis: those with a depression diagnosis were more than 15 times as likely to develop dementia than their peers without depression. But even 20 years later, the risk of dementia remained elevated in those who had depression.

For the second part of the study, the researchers studied more than 25,000 pairs of brothers or sisters, in which one sibling had depression and the other did not. They found that a sibling with depression was more than 20 times as likely to develop dementia than their brother or sister who was not depressed. Again, the risk remained elevated more than two decades later.

The risk of dementia was higher for those with severe depression compared to those with mild depression. There was also a stronger association between depression and vascular dementia, caused by impaired blood flow to the brain, although there was also an increased risk of Alzheimer’s disease.

Earlier studies have shown that symptoms of depression are linked to an increased risk of Alzheimer’s disease. But it is unknown whether depression is a cause or an effect of the disease.

Researchers speculate that in some people, Alzheimer’s could be a long process that begins many years before the actual onset of memory loss, possibly showing up as symptoms of depression in the early stages of the disease. Alternatively, it is also possible that depression may in some way damage the brain, making it vulnerable to the ravages of Alzheimer’s and other forms of dementia.

The current study showed only an association between depression and dementia and could not prove cause and effect. But it was large, following many thousands of people, and had a long follow-up period. In addition, by studying sibling pairs, the researchers sought to control for familial and environmental factors that may affect depression and dementia risk.

The researchers caution that just because you have a depression diagnosis does not mean you will develop dementia. But it may increase your risk. It is possible that getting effectively treated for depression may lower your risk, though more research in this area is needed.

Symptoms of depression are many and varied. They include:

* Feeling sad, apathetic, guilty, worthless or hopeless for weeks to months on end.

* Loss of interest in daily activities, especially ones that used to bring pleasure.

* Poor appetite and weight loss; or increased appetite and excessive weight gain.

* Troubled sleep, waking up repeatedly during the night, or an increased need for sleep, especially at daytime.

* Feeling anxious or agitated and irritable.

* Trouble thinking or an inability to concentrate.

* Focusing on non-serious physical complaints.

If you experience one or more of these symptoms, or other unusual changes in mood or behavior, consult your physician. Medications and therapeutic counseling are available that can provide relief.

By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.

Source: Sofie Holmquist, Anna Nordstrom, Peter Nordstrom: “The association of depression with subsequent dementia diagnosis: A Swedish nationwide cohort study from 1964 to 2016.” PLOS Medicine, Jan. 9, 2020

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