Depression may raise the risk of developing Parkinson's disease, according to a new study.
Researchers from Taipei Veterans General Hospital in Taiwan found that people with depression have a tripled risk of developing Parkinson's disease over a 10-year period compared to those without depression.
However, the study only showed an association, and does not prove that depression causes Parkinson's disease, researchers cautioned. Parkinson's is a chronic condition that involves the loss of dopamine-producing brain cells, and has symptoms of movement problems and tremors.
"Many questions remain, including whether depression is an early symptom of Parkinson's disease rather than an independent risk factor for the disease," study researcher Albert C. Yang, M.D., Ph.D., said in a statement.
The study, published in the journal Neurology, is based on 10 years' worth of data from 4,634 people with depression and 18,544 people without depression. Researchers found that having depression raised the risk of developing Parkinson's disease over the study period by 3.24 times.
In addition, they found that both age and difficult-to-treat depression were independent risk factors for Parkinson's disease.
Depression and Parkinson's have long been known to be intertwined, with the National Institutes of Health saying that symptoms of one condition can make symptoms of the other condition worse, and vice versa. The NIH explained:
For example, people with both illnesses tend to have more movement problems and greater levels of anxiety than those who have just depression or Parkinson's disease. Compared with people who are depressed but do not have Parkinson's, people who have both illnesses may have lower rates of sadness and guilt, but greater problems with concentration.