Do you always look on the dark side of life? Or fret about things no one else even thinks about? If so, here's something new to worry about: Pessimistic and anxious personalities are associated with the development of Parkinson's disease years down the road, researchers say.

"This is the first study to show that people 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, MD, a neurologist at the Mayo Clinic in Rochester, Minn., and a researcher on the study.

The researchers followed nearly 5,000 men and women who took a standardized personality test between 1962 and 1965; 128 of them developed Parkinson's disease over the next 35 to 40 years.

People who scored highest on anxiety scores were 60 percent more likely to develop Parkinson's disease than those scoring lower, Bower says. And those who scored in the top 25 percent on the pessimism scale were 50 percent more likely to develop the progressive neurological disease, he tells WebMD.

The people who developed Parkinson's disease had anxieties that go beyond common worries about what's for dinner or job stress, Bower says. "These are the chronic worriers — the people who worry about things that most people never seem to worry about."

Parkinson's disease, a disorder that affects nerve cells in the part of the brain controlling muscle movement, is characterized by 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.

Which Comes First: Pessimism or Parkinson's?

The new study, presented today at the annual meeting of the American Academy of Neurology, does not show that anxiety or pessimism causes Parkinson's disease — just that there's a link, Bower stresses.

How does he explain the association? "That's still an unanswered question," Bower says.

One possibility is that anxiety and pessimism are risk factors for Parkinson's disease, he says. "Or, they could share a common risk factor such as a gene that makes you prone to both anxiety and Parkinson's."

Ettore Beshi, MD, a neurologist at the Institute for Pharmacological Research in Milan, Italy, offers another explanation. "It could be that symptoms of anxiety and pessimism are the very first signs of the beginning of Parkinson's," he tells WebMD.

Bower says he hopes that future research will shed light on these issues and help doctors learn whether treatment of anxiety or pessimism can help reduce the risk for Parkinson's disease.

Stanley Fahn, MD, a Parkinson's expert at Columbia University in New York and a past president of the American Academy of Neurology, says the findings are bolstered by previous research that hints of a link between certain personality types and risk of Parkinson's disease.

Some studies have shown that risk takers do not tend to develop Parkinson's, he says, while other research suggests that anxiety and depression raise the risk. "This study fits in with this other work," Fahn tells WebMD.

By Charlene Laino, reviewed by Brunilda Nazario, MD

SOURCES: American Academy of Neurology 57th Annual Meeting, April 9-16, 2005, Miami Beach, Fla. James Bower, MD, neurologist, Mayo Clinic, Rochester, Minn. Stanley Fahn, MD, professor of neurology, Columbia University; past president, American Academy of Neurology. Ettore Beshi, MD, neurologist, Institute for Pharmacological Research, Milan, Italy.