In any event, it's important that depression be treated: "Depression is bad for the brain, and so is Parkinson's," Alcalay said.
Dr. David Straker, an adjunct assistant clinical professor of psychiatry at Columbia University Medical Center, agreed that depression should be treated promptly and aggressively. But "we always want to rule out other neurologic diseases when a person has symptoms of depression," he added.
Both depression and Parkinson's disease involve some of the same brain chemicals, notably dopamine, Straker said. He added that certain medications used to treat depression can also cause symptoms of Parkinson's disease. However, antidepressants did not appear to increase risk for Parkinson's in the new study.
Learn more about the causes of Parkinson's disease at the Parkinson's Disease Foundation.
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