Depression Diagnosis Increases Your Risk Of Parkinson's Disease

Michael J. Fox
Actor Michael J. Fox was diagnosed with Parkinson's disease, which has been linked to depression in a comprehensive study from Sweden. Reuters

Parkinson’s disease belongs to a group of conditions called motor system disorders. Symptoms include tremor, rigidity, slowness of movement, and impaired coordination. A comprehensive study from Sweden finds people with depression are more likely to develop this disease.

Beginning at the end of 2005, researchers looked at the records of all Swedish citizens age 50 or older. Then, they identified 140,688 people who’d been diagnosed with depression and matched each of these with three control participants (without depression) of the same sex and birth year. Going forward, the researchers tracked the depressed participants and their controls while also retroactively examining medical records.

During the study period, 1,485 people with depression developed Parkinson's disease, while 1,775 people of those who did not have depression similarly developed the disease. This amounts to 1.1 percent compared to 0.4 percent.

Analyzing the data further, the researchers found Parkinson's disease was diagnosed 4.5 years, on average, after the study began. Generally, the likelihood of developing Parkinson's disease decreased over time. Depressed people were 3.2 times more likely to develop Parkinson's disease within a year of the study’s start date than controls. At 15 to 25 years after the start date, depressed people were about 50 percent more likely to develop the disease.

“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,” Dr. Peter Nordström of Umeå University stated in a press release.

Elusive Cause

Parkinson’s is a result of the loss of dopamine-producing brain cells, yet scientists do not understand what causes the brain changes that lead to Parkinson’s disease. Generally, it is known that men are more likely than women to develop the disease. It also is known that the disease usually begins after age 60. Having a close relative with the disease and ongoing exposure to herbicides and pesticides increases your risk of developing the illness. For these reasons, scientists speculate a blend of genetic and environmental factors contribute to the disease.

In the Swedish study, the seriousness of depression impacted participants' risks of Parkinson's. Anyone who had been hospitalized for depression was 3.5 times more likely to develop Parkinson's disease than depressed people treated only as outpatients. And, compared to those hospitalized for depression just once, people with major depression and hospitalized five or more times were 40 percent more likely to develop Parkinson’s.

When researchers adjusted for other conditions related to depression, such as traumatic brain injury, stroke, and alcohol and drug abuse, the link between this form of mental illness and Parkinson's disease did not change. The researchers also examined siblings. Here, they found no link between one sibling having depression and the other having Parkinson’s disease.

"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," said Nordström.

Source: Gustafsson H, Nordtrom A, Nordstrom P.  Depression and subsequent risk of Parkinson disease A nationwide cohort study. Neurology. 2015.

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