Apr. 20, 2005 ROCHESTER, Minn. -- Mayo Clinic researchers have found that people who score in the upper 25 percent in anxiety level on a personality test have a moderately increased risk of developing Parkinson's disease decades later. They also found a similar link between pessimistic personalities and Parkinson's.
"This is the first study that took a group of people with documented personality characteristics but no symptoms of Parkinson's disease and showed that those with high levels of an anxious or pessimistic personality are at higher risk for developing Parkinson's disease up to several decades later," says James Bower, M.D., Mayo Clinic neurologist and the study's lead investigator.
Although the study demonstrates an association between anxious and pessimistic personality types and Parkinson's, the findings do not provide the exact reason for these links; this will be the subject of further study by the investigators.
"What we have shown in this study is that there's a link between an anxious or pessimistic personality and the future development of Parkinson's," says Dr. Bower. "What we didn't find is the explanation for that link. It remains unclear whether anxiety and pessimism are risk factors for Parkinson's disease, or linked to Parkinson's disease via common risk factors or a common genetic predisposition."
Though the findings demonstrated a higher degree of risk for Parkinson's later in life for those with anxious and pessimistic personality types, the investigators did not find a huge increase in risk.
"We found a significant and definite link between anxious and pessimistic personalities and the future development of Parkinson's disease," says Dr. Bower. "But, the increased risk was relatively small. Just to give you an idea of numbers, if you take 1,000 40-year-olds, about 17 of them will eventually develop Parkinson's disease. If you take 1,000 anxious 40-year-olds, about 27 of them will develop Parkinson's disease."
Dr. Bower explains that the study subjects found to be at risk have anxieties that go beyond common worries about their children's safety or their aging parents' failing health.
"I think it's important to understand that what our study looked at is people with anxious personalities," says Dr. Bower. "These are the chronic worriers -- the people who worry about things that most people don't seem to worry about. Those are the people we're saying have an increased risk of developing Parkinson's disease. We did not look at people who are undergoing some acute, stressful life event or people who have very stressful jobs."
They also found that many subjects who later developed parkinsonism were both anxious and pessimistic at the time of personality testing many years before. This observation suggests that pessimism is linked to anxiety, according to Walter Rocca, M.D., Mayo Clinic epidemiologist and another study investigator.
Dr. Bower explains that this study's findings are not proof that anxiety or pessimism causes Parkinson's. Therefore, risk for Parkinson's should not play a leading role in determining whether to seek medical help, he says.
"I think the important thing to remember is that if you are questioning whether you should seek treatment for anxiety, the decision should be made based on your level of anxiety and how it's impacting your life, and not so much on any potential future risk of Parkinson's disease," says Dr. Bower.
This study does not address whether treatment of anxiety or pessimism can help reduce the risk for Parkinson's disease; however, Dr. Bower indicates that this is an important question he and colleagues hope to address in the future.
Dr. Bower and colleagues conducted this study to determine what types of personality or cognitive style -- one's habitual way of perceiving, remembering, behaving and experiencing emotions -- are associated with the development of Parkinson's disease later in life. Previous work done at Mayo Clinic and at other medical centers had given Dr. Bower's team hints that there might be psychiatric conditions or personality types that might put some people at increased risk for Parkinson's disease.
From an initial group of 7,216 people who took the Minnesota Multiphasic Personality Inventory (MMPI) between 1962 and 1965, the investigators were able to find information on 4,741 of them; 128 had developed Parkinson's disease. The researchers then looked at the MMPI scales for the categories of depression, anxiety, social introversion and pessimism. They found that those who had scored in the top 25 percent in the anxiety and pessimism scales were more likely to have developed Parkinson's disease than those in the bottom 75 percent.
Parkinson's disease is a disorder that affects nerve cells (neurons) in the part of the brain controlling muscle movement. People with Parkinson's often experience trembling, muscle rigidity, difficulty walking, and problems with balance and coordination. These symptoms generally develop after age 50, although the disease affects a small percentage of younger people as well.
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