Depression symptoms that steadily increase in older adults are more strongly linked to dementia than any other types of depression, and, according to Dutch researchers.
Such symptoms may indicate the early stages of the disease, according to the authors of the first ever long-term study to examine the link between dementia and the course of depression.
“Depressive symptoms that gradually increase over time appear to better predict dementia later in life than other trajectories”
Symptoms of depression are common with dementia, but previous studies have often looked at single episodes of depression, failing to take into account how depression develops over time.
The new study, published in The Lancet Psychiatry journal, included 3,325 adults aged 55 and over, who all had symptoms of depression but no symptoms of dementia at the start. The researchers tracked depressive symptoms over 11 years and dementia risk for a further 10.
They identified five different trajectories of depressive symptoms – low, initially high that decreased, low starting scores that increased then remitted, initially low that increased, and constantly high.
Overall, 434 study participants developed dementia, including 348 cases of Alzheimer’s disease.
Among the group with low symptoms of depression, 10% developed dementia. The researchers used this as the benchmark against which to compare other trajectories of depression.
Only those whose symptoms of depression increased over time were at increased risk of dementia – 22% of people in this group developed dementia.
Individuals with remitting symptoms of depression were not at an increased risk of dementia, compared to individuals with low depressive symptoms.
As a result, the authors suggested that having severe symptoms of depression at one point in time does not necessarily have any lasting influence on the risk of dementia.
The authors said their findings supported the hypothesis that increasing symptoms of depression in older age could potentially represent an early stage of dementia.
They also said the findings supported previous suggestions that dementia and some forms of depression may be symptoms of a common cause.
They noted that biological mechanisms of depression and neurodegenerative diseases overlapped, including loss of ability to create neurons, increased cell death and immune system dysregulation.
Depression symptoms ‘linked to higher dementia risk’
Study author Dr Arfan Ikram, from Erasmus University Medical Center in Rotterdam, said: “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.
“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.
He added: “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.”