Seniors who are suffering from depression appear to have nearly double the risk of developing dementia later on, researchers report.
The researchers behind the study say it's unclear from their findings whether depression actually causes dementia, but they say it's possible and say there are a number of ways depression could impact dementia risk.
For the study, 949 people who took part in the Framingham Heart Study were recruited for this study. The average of the seniors was 79 and all of them were free of dementia at the start of the study.
Researchers from the University of Massachusetts Medical School tested the subjects for the symptoms of depression, asking them questions about general depression, sleep complaints, social relationships and other factors.
A total of 125 people, or 13 per cent, were classified as having depression at the start of the study.
The participants were then followed for up to 17 years. At the end of the study, 164 people had developed dementia with 136 specifically diagnosed with Alzheimer's disease.
Nearly 22 per cent of people who were depressed at the start of the study developed dementia compared to about 17 per cent of those who were not depressed, a 70 per cent increased risk in those who were depressed.
The results were the same regardless of a person's age, sex, education and whether they had a key gene that increases a person's risk of Alzheimer's disease, called APOE, the researchers report in the journal Neurology.
Study author and neuroepidemiologist Dr. Jane Saczynski says it remains unclear whether depression causes dementia, but she says there are a number of ways depression might impact the risk.
She explains that when a person is depressed, their brain tissue can become inflamed, which might put one at risk of dementia. As well, certain proteins in the brain that increase with depression may also increase the risk of developing dementia.
It's also possible that people with long-term depression are prone to lifestyle factors, such as poor diet, a lack of exercise and decreased social time, which could also affect whether they develop dementia.
Saczynski hopes the study, which is one of the largest and longest population based studies to date, helps clear up confusion over earlier studies that reported inconsistent results about the link between depression and dementia.
