Depression as a risk factor for dementia: Link is independent of dementia-related brain changes

"Studies have shown that people with symptoms of depression are more likely to develop dementia, but we haven't known how the relationship works," said study author Robert S. Wilson, PhD, neuropsychiatrist at the Rush Alzheimer's Disease Center and lead study investigator. "Is the depression a consequence of the dementia? 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?"

The current study indicates that the association of depression with dementia is independent of dementia-related brain changes. "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," Wilson said.

The study involved 1,764 people from the Religious Orders Study and the Rush Memory and Aging Project with an average age of 77 who had no thinking or memory problems at the start of the study. Participants were screened every year for symptoms of depression, such as loneliness and lack of appetite, and took tests on their thinking and memory skills for an average of eight years. A total of 680 people died during the study, and autopsies were performed on 582 of them to look for the plaques and tangles in the brain that are the signs of dementia and other signs of damage in the brain.

During the study, 922 people, or 52 percent of the participants, developed mild cognitive impairment (MCI), or mild problems with memory and thinking abilities that is often a precursor to Alzheimer's disease. A total of 315 people, or 18 percent, developed dementia.

The researchers found no relationship between how much damage was found in the brain and the level of depression symptoms people had or in the change in depression symptoms over time.

People who developed mild cognitive impairment were more likely to have a higher level of symptoms of depression before they were diagnosed, but they were no more likely to have any change in symptoms of depression after the diagnosis than people without MCI. People with dementia were also more likely to have a higher level of depression symptoms before the dementia started, but they had a more rapid decrease in depression symptoms after dementia developed.

Having a higher level of depression symptoms was associated with more rapid decline in thinking and memory skills, accounting for 4.4 percent of the difference in decline that could not be attributed to the level of damage in the brain.

The study was supported by the National Institute on Aging and the Illinois Department of Public Health.