Depression doubles dementia risk, say researchers

Having depression may nearly double the risk of developing dementia later in life, new research suggests.

Experts know that the two conditions often co-exist, but it is not clear if one actually leads to the other.

To reach the conclusion, researchers examined research data on 949 people with an average age of 79 from the Framingham Heart Study.

At the start of the study, participants were free of dementia and were tested for depressive symptoms based on 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 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 10-year absolute risk for dementia was 0.21 in people without depressive symptoms and 0.34 in people with depressive symptoms.

The results were the same regardless of a person’s age, sex, education and whether they had the APOE gene that increases a person’s risk of Alzheimer’s disease.

“While it’s unclear if depression causes dementia, there are a number of ways depression might impact the risk of dementia,” said study author Jane Saczynski, with the University of Massachusetts Medical School in Worcester, MA.

Now two studies published in the American journal Neurology suggest depression does mean dementia is more likely, although they do not show why.

And the researchers stress that the findings merely reveal a link, not a direct cause.

They say more studies are needed to find out why the two conditions are linked.

They believe brain chemistry and lifestyle factors like diet and the amount of social time a person engages in may play a role.

What this study demonstrates is that depression at a younger age is probably a significant risk factor for dementia.