Do you suffer from depression? You may have a higher risk of developing Parkinson’s disease later in life.
Researchers studied approximately 140,000 Swedish adults ages 50 and older who had been diagnosed with depression. Each was then matched with three adults of the same gender and year of birth who had not been diagnosed with depression as “control” subjects, bringing the total number of participants to more than 400,000 adults.
Looking for the link to Parkinson’s
The participants were then followed for up to 26 years. During this time, 1,485 people with depression developed Parkinson’s disease, or 1.1 percent, while 1,775 people, or 0.4 percent of those who did not have depression, developed Parkinson’s disease.
“We saw this link between depression and Parkinson’s disease during a time span 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 study author Peter Nordström, PhD, at UmeÃ¥ University in UmeÃ¥, Sweden, in a press release from the American Academy of Neurology. The study was published online May 20 in Neurology, the academic research journal of the American Academy of Neurology.
The link between depression and Parkinson’s made headlines last year after performer Robin Williams committed suicide. His wife said Williams had struggled with both disorders, though findings after his death suggested he also suffered from a form of dementia that may have contributed.
Does it run in the family?
For the study, researchers also examined siblings, and found no link between one sibling having depression and the other having Parkinson’s disease. “This finding gives us more evidence that these two diseases are linked,” said 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.”
Parkinson’s disease was diagnosed an average of 4.5 years after the start of the study. The likelihood of developing Parkinson’s disease decreased over time. People with depression were 3.2 times more likely to develop Parkinson’s disease within a year after the study started than people who did not have depression. By 15 to 25 years after the study started, people with depression were about 50 percent more likely to develop Parkinson’s disease.
Severity makes a difference
People with more serious cases of depression were also more likely to develop Parkinson’s disease. People who had been hospitalized for depression five or more times were 40 percent more likely to develop Parkinson’s disease than people who had been hospitalized for depression only one time. People who had been hospitalized for depression were also 3.5 times more likely to develop Parkinson’s disease than people who had been treated for depression as outpatients.
The link between depression and Parkinson’s disease did not change when researchers adjusted for other conditions related to depression, such as traumatic brain injury, stroke and alcohol and drug abuse.
The study was supported by the Swedish Research Council.
The Parkinson’s Disease Foundation estimates 40 percent of people with Parkinson’s develop clinical depression at some point during the course of the disease, though one recent U.S. study found about 14 percent of Parkinson’s patients have depression. The organization has called for greater research and education of medical professionals regarding the prevalence of depression in adults affected by Parkinson’s disease.
