Is depression an early sign of dementia? Is it an emotional response to losing cognitive abilities? Or is depression a risk factor for dementia? In a new study, researchers sought to discern the timing and the underpinnings of the link between depression and dementia.
They looked at 13,535 individuals who participated in a voluntary health exam from 1964-1973; during those years, participants were between 40 and 55 years of age. They used the results from the health exam to determine which participants exhibited depressive symptoms.
The researchers found that depressive symptoms in midlife or late in life were associated with an increased risk of developing dementia. Participants who evidenced midlife depressive symptoms were 20% more likely to develop dementia, while individuals who became depressed late in life were 70% more likely to develop dementia. Those who showed depressive symptoms in both midlife and late in life were 80% more likely to develop dementia.
The study also looked at particular types of dementia: Alzheimer’s disease (the most common type) and vascular dementia (which results from impaired blood flow to the brain). The findings revealed that chronic depression was associated with an increased risk of vascular dementia: those who evidenced depressive symptoms both in midlife and late in life had a three times greater chance of developing vascular dementia. The risk of Alzheimer’s was approximately doubled in individuals with depressive symptoms in late life.
So, is depression an early symptom of dementia, or is depression a risk factor? Researchers conclude that it depends on the subtype: for Alzheimer’s, depression late in life may reflect the earliest symptoms, while for vascular dementia, chronic depression or depression that recurs later in life may represent a risk factor that predisposes people to the development of vascular dementia.
This study can have a profound impact on treatment, as it can form the basis of future studies to determine whether treatment of depression in midlife or in late life may help to maintain people’s cognitive abilities and delay dementia onset. As the study’s authors conclude, “even a small reduction in dementia risk would have a tremendous public health impact.”