New research indicates that people with depressive symptoms in later life are more likely to develop dementia than those of a similar age without depression.
The team of scientists in the US set out to determine how depression is linked to the onset of dementia. 1,764 participants took part in the study, recruited from two ongoing projects: the Religious Orders Study and the Rush Memory and Aging Project. The volunteers, with an average age of 77, were assessed annually for memory and thinking skills, as well as completing assessments for depressive symptoms, using a ten-item questionnaire. The score, from 1-10, relates to the number of depressive symptoms the volunteer identified with. Of the total number of participants, 701 went on to develop mild-cognitive impairment, a condition that often precedes dementia. A further 315 developed dementia in the follow-up period that lasted on average just under 8 years.
These tests indicated that those who had depressive symptoms were more likely to develop dementia within the follow-up period. They also revealed that while depressive symptoms did not worsen with dementia onset, a greater number of depressive symptoms prior to diagnosis were linked to a faster deterioration in thinking and memory skills.
In a subset of study participants, brain samples were studied after death. The authors revealed that the typical hallmarks of dementia, such as the build-up of toxic proteins, amyloid and tau, were not related to the number of depressive symptoms. This indicates that depression is altering the progression of dementia in a way that is not linked to the biological changes that are typically associated with the condition.
Dr Simon Ridley, Head of Research at Alzheimer’s Research UK, said:
“Studies have previously shown links between depression and dementia but it is difficult to tease apart depressive symptoms from the onset of cognitive problems or to assess whether depression is a cause or consequence of dementia. This study indicates that depression contributes to the decline in cognition in dementia, but as a diagnosis of depression did not alter typical brain changes involved in dementia, we still don’t know how depression alters the symptoms seen in the condition. We still need to find out whether treatments to tackle depression can alter the course of dementia.
“In light of recent finding that 1 in 3 cases of dementia could be preventable, it is important to understand how existing health conditions and lifestyle factors alter the risk of dementia, so that changes can be made where possible to maintain brain health in later life.”