Depression symptoms that steadily increase in older adults are more strongly linked to dementia than any other types of depression, according to new research.
The new study, published in The Lancet Psychiatry journal, notes that the steadily increasing depression symptoms may actually indicate the early stages of dementia.
Symptoms of depression are common in people with dementia, but previous studies have often looked at single episodes of depression, failing to take into account how depression develops over time, researchers said.
The course of depression varies greatly between individuals, they said. Researchers note that some people might experience depressive symptoms only transiently, followed by full remission, while others might have remitting and relapsing depression, while still others might be chronically depressed.
Different courses of depression may reflect different underlying causes, and might be linked to different risks of dementia, according to the researchers.
The new study included 3,325 adults aged 55 and over, who all had symptoms of depression, but no symptoms of dementia at the start of the study.
Data was gathered from the Rotterdam Study, a population-based study of various diseases in the Netherlands that allowed the researchers to track depressive symptoms over 11 years and the risk of dementia for a subsequent 10 years.
Using the Center for Epidemiology Depression Scale (CES-D) and the Hospital Anxiety and Depression Scale-Depression (HADS-D), the researchers identified five different trajectories of depressive symptoms:
- Low depression symptoms (2,441 participants);
- Initially high symptoms that decreased (369);
- Low starting scores that increased, then remitted (170);
- Initially low symptoms that increased (255); and,
- Constantly high symptoms (90).
Of the 3,325 participants, 434 developed dementia, including 348 cases of Alzheimer’s disease.
Among the group with low symptoms of depression, 10 percent (or 226) developed dementia.
The researchers said they used this as the benchmark against which to compare other trajectories of depression as the study did not compare the risk of dementia following depression with the risk of dementia for adults without depression.
Only the group whose symptoms of depression increased over time was at an increased risk of dementia — 22 percent, or 55 people, developed dementia, according to the study’s findings.
This risk was particularly pronounced after the first three years, the researchers reported.
Individuals with remitting symptoms of depression were not at an increased risk of dementia compared to individuals with low depressive symptoms, according to the study’s findings.
The researchers say this suggests that having severe symptoms of depression at one point in time does not necessarily have any lasting influence on the risk of dementia.
The researchers add their findings support the hypothesis that increasing symptoms of depression in older age could potentially represent an early stage of dementia.
They also say that the findings support previous suggestions that dementia and some forms of depression may be symptoms of a common cause. They explain that at the molecular levels, the biological mechanisms of depression, and neurodegenerative diseases overlap considerably, including the loss of ability to create new neurons, increased cell death and immune system dysregulation.
“Depressive symptoms that gradually increase over time appear to better predict dementia later in life than other trajectories of depressive symptoms, such as high and remitting, in this study,” said Dr. M. Arfan Ikram, of the Department of Epidemiology at Erasmus University Medical Center in Rotterdam.
“There are a number of potential explanations, including that depression and dementia may both be symptoms of a common underlying cause, or that increasing depressive symptoms are on the starting end of a dementia continuum in older adults,” he said. “More research is needed to examine this association, and to investigate the potential to use ongoing assessments of depressive symptoms to identify older adults at increased risk of dementia.”