Parkinson's Disease Risk Higher for Adults Diagnosed With Depression, Research Shows

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Individuals who have been clinically diagnosed with depression have an increased risk of developing Parkinson's disease later on. A Swedish study has found a link between the two.

A comprehensive study that utilized 26 years worth of data from 400,000 Swedes, aged 50 and above, was published in the journal Neurology on Wednesday.

According to Live Science, the researchers looked at more than 140,000 Swedish citizens who have depression and matched them with three other people of the same sex and age who do not have depression. The participants of the study were at least 50 years old by 2005.

The scientists found that 1.1% of the people in the study who have depression developed Parkinson's, and 0.4% of those who did not have depression developed Parkinson's disease, according to Eureka Alert.

"We saw this link between depression and Parkinson's disease during 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," said Dr. Peter Nordström of Sweden's t Umeå University.

Scientists also examined data from siblings and found that there is no connection between one sibling with depression and the other with Parkinson's.

"This finding gives us more evidence that these two diseases are linked," Nordström said. "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 Swedish study suggested that the more severe the person's depression is, the greater is his chance of developing Parkinson's. In a report by Medical Daily, any individual who has been hospitalized for depression has a 3.5 times increased risk of having Parkinson's than depressed outpatients.

However, the study doesn't necessarily mean that Parkinson's is caused by depression, according to James Beck, of the US Parkinson's Disease Foundation, who was not involved in the study.

"I think the bigger message is that depression and Parkinson's disease really go hand in hand," Beck told NBC News. "We have known that before, but this is a very large study."

He says that the majority of people who do get diagnosed with Parkinson's learn late about their condition because they wait until the symptoms become more apparent. Although there is no cure, early detection could lead to the delay and management of the disease's worst symptoms.

NBC News pointed out that the association of depression to Parkinson's in media was partly due to comedian Robin William's death and the report that the actor was struggling with both.

"Understanding how depression occurs still remains a mystery," Beck said. "There is something about the Parkinson's disease brain that leads to depression."