Depression could be linked to increases in a person's risk of developing dementia, even independently of the biological factors that are typically related to the onset of the condition.
This is according to the findings of a new study carried out by scientists from Rush University Medical School, which has been published in the medical journal Neurology.
A total of 1,764 people from the Religious Orders Study and the Rush Memory and Aging Project with an average age of 77 took part in the trial.
No thinking or memory problems were identified in these individuals at the start of the study. Every year after the start of the research, the participants were screened for symptoms of depression, such as loneliness and lack of appetite.
Tests were also carried out to measure their thinking and memory skills for an average of eight years - although 680 people died during the course of the study.
Some 922 participants - 52 per cent - developed mild cognitive impairment or similar issues with cognitive function that are often seen as a precursor to Alzheimer's disease. A further 18 per cent developed dementia.
Study author Dr Robert Wilson, neuropsychiatrist at the Rush Alzheimer's Disease Center, underlined the fact that previous studies have so far failed to identify the link between depression and dementia.
Dr Doug Brown, director of research and development at the Alzheimer's Society, said the findings raise the possible idea that treatment of depression could be an effective means of reducing the risk of developing this form of cognitive decline.
"We've long known that there is a link between depression and dementia but it hasn't been clear whether depressive symptoms could be early symptoms of the changes occurring in the brain or a risk factor," he commented.
"This interesting study suggests that depression could be a risk factor, separate from the biological processes thought to cause dementia," Dr Brown continued.
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