Strong link between depression and dementia found

The study, published Monday in the journal JAMA Neurology, used data from more than 1.4 million Danish citizens followed from 1977 to 2018, said study lead author Dr. Holly Elser, an epidemiologist and neurology resident at the University of Pennsylvania.

The study said people were diagnosed with depression or not and were followed for years to see who developed dementia later in life. The researchers controlled for factors such as education, income, cardiovascular disease, diabetes, substance use disorders and bipolar disorder, CNN reports.

The large dataset and multiple analyzes the researchers used made their findings strong and reliable, but the study is limited by the inaccessibility of information such as genetic data, said Dr Natalie Marchant, assistant professor of psychiatry at University College London.

According to Dr. Holly Elser, depression in adulthood is often considered an early symptom of dementia, and many previous studies have linked the two. But the latest study also shows an association between dementia risk and depression diagnoses in early and middle age.

“Thus, our results provide strong evidence that depression is not only an early symptom of dementia, but that depression increases the risk of developing dementia,” she said.

Although the link between depression and dementia has been shown to be strong, there are still questions that the study does not answer, CNN emphasizes.

“For example, there may be common risk factors for depression and dementia that occur early in life, depression may increase the risk of dementia due to altered levels of key neurotransmitters, or depression may lead to changes in health behavior that in turn increase the risk of dementia,” added Dr. Holly Elser.

“There is a clear need for future research that explores potential mechanisms linking depression in early adulthood to the subsequent development of dementia,” notes Elser.

According to Natalie Marchant, another part of the results that might warrant further study is the stronger association found in men than in women.

“This is an interesting find that I hope will be further explored,” she added. “This reinforces the idea that we need to routinely review risk factors for dementia in men and women separately, as different mechanisms may be involved.”

The latest study looked at antidepressant treatment up to six months after diagnosis and found no difference in risk between treated and untreated groups, Dr. Elser said.

She added that more research into whether drug and cognitive behavioral therapies of varying timing and duration are effective in reducing risk will be important to move forward.

Preliminary results from other observational studies suggest that older adults who took part in therapy that reduced their symptoms of depression and/or anxiety also had a reduced risk of developing dementia in the future, Natalie Marchant added. However, because the studies were observational, the researchers cannot say whether the therapy resulted in a reduction in the incidence of dementia, she added.

“However, taking care of your mental health is certainly still important to your well-being in the present,” Marchant emphasizes.

Holly Elser agrees that, regardless of the risk of developing dementia, treating depression should be a priority.

“Because depression is so common and associated with significant individual and societal costs, effective treatment of depressive symptoms should be a priority, whether or not they increase the risk of developing dementia later in life,” she said.