People who suffer from depression were much more likely to develop Parkinson's disease later in their lives, according to a new study that strengthens the theory that depression and Parkinson's are linked, NBC News reported. The study, published team of Swedish researchers, tracked the entire population of Swedish people who were over 50 by the end of 2005. Of the 140,000 people in the study diagnosed with depression between 1987 and 2012, about 1 percent eventually developed Parkinson's — compared to only about .4 percent who were never diagnosed with depression. "Depression may be a very early symptom of Parkinson's disease or a risk factor for the disease," Peter Nordström of Umea University, who led the study, said in a statement. But James Beck, the vice president of scientific affairs at the U.S. Parkinson's Disease Foundation, cautions that depression does not necessarily causes Parkinson's. "The bigger message is that depression and Parkinson's disease really go hand in hand," Beck told NBC News.