People who have had depression are more likely to develop Alzheimer’s disease than people who have never had depression, according to a study published in the April 8, 2008, issue of Neurology®, the medical journal of the American Academy of Neurology.

The study involved 486 people age 60 to 90 who had no dementia. Of those, 134 people had experienced at least one episode of depression that prompted them to seek medical advice.

The participants were followed for an average of six years. During that time 33 people developed Alzheimer’s disease. People who had experienced depression were 2.5 times more likely to develop Alzheimer’s disease than people who had never had depression. The risk was even higher for those whose depression occurred before the age of 60; they were nearly four times more likely to develop Alzheimer’s than those with no depression.

“We don’t know yet whether depression contributes to the development of Alzheimer’s disease or whether another unknown factor causes both depression and dementia,” said study author Monique M.B. Breteler, MD, PhD, with the Erasmus University Medical Center in Rotterdam, the Netherlands. “We’ll need to do more studies to understand the relationship between depression and dementia.”

One theory was that depression leads to loss of cells in two areas of the brain, the hippocampus and the amygdala, which then contributes to Alzheimer’s disease. But this study found no difference in the size of these two brain areas between people with depression and people who had never had depression.

The study also assessed whether the participants had symptoms of depression at the start of the study. But those with depressive symptoms at the start of the study were not more likely to develop Alzheimer’s than those with no depression at the start of the study.

The study was supported by the Netherlands Organization for Scientific Research and the Health Research and Development Council.

The American Academy of Neurology, an association of more than 21,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as stroke, Alzheimer’s disease, epilepsy, Parkinson’s disease, and multiple sclerosis.

Source: American Academy of Neurology (AAN)