Study Suggests Link Between Depression and Parkinson’s Disease

According to a recent study, people with depression may be more likely to develop Parkinson’s disease.

The researchers used a cohort consisting of all Swedish citizens who were aged 50 or above at the end of 2005. The 140,688 people from this group who were diagnosed with depression between 1987 and 2012 were compared to a total of 421,718 control participants in the same age group who had not been diagnosed with depression. All participants were then followed up for up to 26 years. During this time, a total of 1,485 (1.1%) of those with depression developed Parkinson’s disease, as opposed to 1,775 (0.4%) of the much larger control group.

“We saw this link between depression and Parkinson’s disease over a timespan of more than two decades, so depression may be a very early symptom of Parkinson’s disease or a risk factor for the disease,” says study co-author Professor Peter Nordström, of Umeå University in Sweden.

Overall, the researchers calculated that participants with depression were 3.2 times more likely to develop Parkinson’s within a year of the study than those without. After 15-25 years, those with depression were almost 50% more likely to develop the condition.

Furthermore, the study involved an analysis of siblings to rule out the likelihood of the increase in risk being caused by genetic factors. There was no link found between one sibling having Parkinson’s disease and the other having depression.

“This finding gives us more evidence that these two diseases are linked,” says Professor Nordström. “If the diseases were independent of each other but caused by the same genetic or early environmental factors, then we would expect to see the two diseases group together in siblings, but that didn’t happen.”

The study authors suggest that depression or antidepressive treatment may increase the risk of Parkinson’s disease, or that depression may be an early symptom of the condition. However, the study was an observational one so causation could not be determined.