The Disturbing Link Between Depression and Dementia

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Who hasn't been depressed? For many of us, depression is just a passing cloud. This depression is self-limiting, and very responsive to the comforts of a sympathetic friend or melancholy music, to distraction or ice cream. This "depression," once called "feeling blue," is part of the color palette of emotional life.

Serious depression is another matter altogether. It is a crippling disorder that blocks out the sun and steals hope. Serious depression impacts family and friends; it is contagious and, too often, can even be deadly.

Psychologists and others who work with the elderly have long observed the association of late-life depression with dementia. Depression often appears as the first sign of dementia. A large, recent study conducted in Denmark discovered that serious depression, diagnosed even in early or mid-life, is associated with an increased risk of dementia years later. The risk of dementia was more than doubled for both men and women with diagnosed depression. The persistent association between dementia and depression diagnosed in early and middle life suggests that depression may increase dementia risk.

Holly Elser and associates examined a nationwide cohort study of Danish citizens and matched for age and sex people with a depression diagnosis with those with no depression diagnosis. They followed this sample of more than 200,000 individuals from 1977 to 2018. The hazard of developing dementia among those diagnosed with depression was 2.41 times that of the comparison cohort, regardless of how many years elapsed from the time of initial diagnosis.

This is a very important study that raises myriad follow-up questions for researchers, both for the understanding of the biological and neurological aspects of depression and its treatment. The study has major public health ramifications. Given the increase in depression diagnoses in younger and younger patients, and the increase in life expectancy, these findings are an urgent call to research and health policy.

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