People who suffer from depression could have a higher risk of developing Parkinson's disease, a recent study found.
The large study looked at all Swedish citizens age 50 and older at the end of 2005 and narrowed them down to a sample size of 40,688 people who were diagnosed with depression between 1987 and 201, Umeå University reported. These participants were matched with three control participants of the same age and gender who had never been diagnosed with depression.
"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 study author Peter Nordström of Umeå University.
The study subjects were followed for up to 26 years, and during this follow-up period 1,485 people with depression developed Parkinson's disease (1.1) percent, compared to the 1,775 people (0.4 percent) who developed Parkinson's but did not suffer from depression.
Parkinson's disease was diagnosed an average of 4.5 years following the start of the study, and after that the likelihood of a Parkinson's diagnosis decreased. The findings shows people who were hospitalized for depression five or more times were 40 percent more likely to develop Parkinson's than those who had only been hospitalized once. The study also suggested people who had been hospitalized for depression were 3.5 times more likely to develop Parkinson's than those who had been treated as outpatients.
The researchers also analyzed pairs of siblings, and did not find a link between one sibling having depression and the other developing Parkinson's disease.
"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 findings were published in a recent edition of the journal Neurology.
