Depression Increases the Risk of Dementia by Twofold

According to a study conducted in collaboration between researchers at the University of Pennsylvania’s Perelman School of Medicine and Aarhus University in Denmark, those diagnosed with depression, including young and middle-aged adults, were more than twice as likely to be diagnosed with dementia later in life as those who did not have depression. The study is the most comprehensive of its type, with data from 1.4 million Danish residents collected over nearly four decades. The findings were reported in JAMA Neurology this week.

“While depression diagnosed later in life is generally thought to be an early symptom of dementia, our results suggest that a depression diagnosis at any point in adulthood increases the risk of this condition later on,”  said first author, Holly Elser, MD, PhD, a Neurology resident at Penn. “Previous studies with smaller sample sizes and shorter follow-up times have consistently illustrated the link between this mental health condition and depression diagnosed later in life, but with our long-term analysis, we were able to precisely estimate the association between dementia and depression over an individual’s life span.”

Depression and dementia are both widespread diseases, with depression affecting an estimated 20 million American adults and dementia impacting an estimated 5 million individuals, with the latter number expected to rise to almost 14 million by 2060. Depression is a mood condition marked by feelings of hopelessness, thoughts of death, and even suicidal ideation. Dementia is defined as the reduced ability to remember, think, or make judgments, which interferes with daily activities. The most frequent type of dementia is Alzheimer’s disease.

Since the late 1970s, regular and prospective health data for all Danish citizens has been collected and recorded for Danish National Health Registers. Researchers examined the health records of nearly 1.4 million Danish inhabitants and identified approximately 246,500 people who received a new depression diagnosis between 1980 and 2018. A comparison cohort of almost 1,190,300 persons free of depression were drawn at random from the Danish general population. 14,000 people were diagnosed with dementia after being diagnosed with depression. In the comparison group, approximately 38,650 people were diagnosed with this condition, indicating that those who had previously been diagnosed with depression were 2.41 times more likely to be diagnosed with dementia later in life.

The link between depression and dementia maintained for both men and women, regardless of whether depression was diagnosed in early, middle, or late life, albeit the link between depression and dementia was higher in men. Multiple inpatient hospitalizations for depression were linked to an increased risk of this condition later in life, with the risk increasing with each additional hospitalization. Researchers discovered that taking an antidepressant within six months of being diagnosed with depression had no effect on the rate of dementia diagnosis later in life.

The researchers acknowledge the paper’s limitations and emphasize the importance of future research into the link between depression and dementia.

“It is still unclear what about depression increases the risk of a dementia diagnosis, and I hope to see further research that evaluates whether the link between depression and dementia may be biological, a result of behaviors associated with depression like social isolation and other changes in key health behaviors, or some combination of these mechanisms,” said Elser. “What’s more, since depression affects so many individuals, research that examines whether clinical practices to manage depression can reduce the risk for dementia in individuals diagnosed with depression.”

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