Researchers say the link between depression and dementia is independent of brain changes caused by dementia.
"Is the depression a consequence of the dementia?" he asks. "Do both problems develop from the same underlying problems in the brain? Or does the relationship of depression with dementia have nothing to do with dementia-related pathology?"
In an attempt to answer these questions, Wilson and colleagues analyzed 1,764 people of an average age of 77, who were a part of the Religious Orders Study and the Rush Memory and Aging Project.
All participants were free of any memory or thinking problems at study baseline. Each year for an average of 7.8 years, subjects were assessed for symptoms of depression, such as reduced appetite and loneliness, and took part in tests that gauged their memory and thinking skills.
Link between depression and dementia 'independent of dementia-related brain changes'
During the study period, 680 people died. Autopsies were performed on 582 of these individuals to identify any brain plaques or tangles related to dementia, as well as any other indications of brain damage.
The researchers found that 315 (18%) participants developed dementia during the study period, while 922 (52%) participants developed mild cognitive impairment (MCI) - a condition that is a common precursor to Alzheimer's disease, the most common form of dementia.
According to the researchers, no relationship was found between the levels of brain damage among participants and the levels of depressive symptoms or changes in depressive symptoms. This indicates that the relationship between depression and dementia is independent of the brain changes caused by dementia, the team says.
The investigators found that those who developed MCI were more likely to have a higher level of depressive symptoms prior to MCI diagnosis. However, compared with those who did not develop MCI, they were no more likely to experience any change in symptoms of depression following MCI diagnosis.
Participants who developed dementia were also more likely to have a higher level of depressive symptoms before dementia diagnosis, according to the researchers. But after diagnosis, their depressive symptoms were more likely to reduce rapidly.
Overall, having a higher level of depressive symptoms was linked to faster cognitive decline, according to the researchers. They note that depressive symptoms accounted for 4.4% of the variability in cognitive decline that could not be attributed to levels of brain damage.
Commenting on the study results, Wilson says:
"These findings are exciting because they suggest depression truly is a risk factor for dementia, and if we can target and prevent or treat depression and causes of stress, we may have the potential to help people maintain their thinking and memory abilities into old age."
Medical News Today recently reported on a study by researchers from the Gladstones Institute in San Francisco, CA, and the University of California-San Francisco, detailing how they restored memory and learning deficits in Alzheimer's mouse models.