Depression in Old Age May Be Linked to Dementia, Study Finds

The reasons some people are more at risk for developing dementia came into clearer focus today thanks to a new study that suggests a link between depression and dementia.

Researchers from Erasmus Medical Center in the Netherlands found that older people who developed increasingly worse depression were more likely to develop dementia, according to a study published today in the Lancet medical journal.

Researchers examined 3,325 people older than 55, who had been followed as part of a population study since 1990. They measured the level of depressive symptoms and then checked to see whether those with signs of depression went on to develop dementia. They found that 21 percent of people whose depressive symptoms increased over time ended up being diagnosed with dementia. By comparison, only 10 percent of people with "low symptoms of depression" developed dementia.

The researchers explained that signs of depression may be an early signal that dementia is developing in the brain before the telltale signs of memory loss appear later on. They point out previous studies have suggested psychological changes can lead to depression, including one study that found that atrophy of the brain may trigger depression.

Additionally, inflammation in the brain is seen in episodes of depression and cognitive decline and may also be key to understanding this link.

"Depressive symptoms that gradually increase over time appear to better predict dementia later in life than other trajectories of depressive symptoms …," said Dr. M. Arfan Ikram, co-author of the study and epidemiologist at the Erasmus University Medical Center, Rotterdam, Netherlands, in a statement today. "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."

Ikram said there should be more studies to fully understand the association.

In a published comment accompanying the study, Dr. Simone Reppermund of the Department of Developmental Disability and Centre for Healthy Brain Ageing at the University of New South Wales, Sydney, Australia, said research still needed to be done to understand the "underlying mechanisms" of depression and dementia.

"The questions are if, and how, the presence of depression modifies the risk for dementia," Reppermund said. "The study … provides an answer to the first question: Depression, especially steadily increasing depressive symptoms, seems to increase the risk for dementia. However, the question of how the presence of depressive symptoms modifies the risk of dementia still remains."

Experts said the study joins a growing body of evidence finding that depression and dementia seem to have some overlapping aspects.

Dr. Philipp Dines of the Geriatric Psychiatry Department at University Hospitals in Cleveland said the study highlights how complex dementia symptoms can be and how they affect so much more than just cognition.

“It shows that these neurocognitive degenerative illnesses are complex entities that involve multiple aspects of brain function,” Dines said. “It’s not just cognitive pieces, it also affects the whole make up of who we are.”