"The association with Parkinson's disease is increased to almost three times that of someone who does not have allergic rhinitis," says James Bower, M.D., Mayo Clinic neurologist and lead study investigator. "That's actually a pretty high elevation."

Previous studies had shown that people who regularly take nonsteroidal anti-inflammatory drugs, such as ibuprofen, are less likely to develop Parkinson's disease. These results prompted the Mayo Clinic investigators to look further into the links between diseases characterized by inflammation and Parkinson's. They studied 196 people who developed Parkinson's disease, matched with people of similar age and gender who did not develop Parkinson's. The study was conducted in Olmsted County, Minn., home of Mayo Clinic, over a 20-year period.

The researchers examined these groups to determine if those who developed Parkinson's disease had more inflammatory diseases. They found that those with allergic rhinitis were 2.9 times more likely to develop Parkinson's. They did not find a similar association between inflammatory diseases such as lupus, rheumatoid arthritis, pernicious anemia or vitiligo and Parkinson's disease. The researchers hypothesize that they may not have found significant links between these diseases and Parkinson's disease due to the relatively small number of those in the population who have these diseases, and thus the small number with these diseases in their population sample study. They also did not find the same association with Parkinson's disease in patients with asthma that they discovered in those with allergic rhinitis.

Dr. Bower says that this study did not examine patients' types of allergies or when they developed allergies.

The investigators theorize that a tendency toward inflammation is the key link between the diseases.

"People with allergic rhinitis mount an immune response with their allergies, so they may be more likely to mount an immune response in the brain as well, which would produce inflammation," Dr. Bower says. "The inflammation produced may release certain chemicals in the brain and inadvertently kill brain cells, as we see in Parkinson's."

Dr. Bower explains that this study does not prove that allergies cause Parkinson's disease; instead, it points to an association between the two diseases. He advises that allergy patients can do little to reduce the potential risk for Parkinson's.

"I wouldn't worry if you have allergies," he says. "Treat the allergy symptoms you have to alleviate them at the time. At this point, we have no good evidence that this treatment will protect you from possibly developing Parkinson's disease later."

Dr. Bower and colleagues hope, however, that the clues in this study may give scientists a strong hint about inflammation's role in Parkinson's.

"This is exciting, because we may be able to develop medications to block the inflammation," he says.

Parkinson's is a complex disease, says Dr. Bower, because many factors can contribute to its development and its causes can differ. The complexity can be compared to heart attacks, which can be caused by hypertension, high cholesterol or smoking, among other factors. Thus, allergic rhinitis would now be considered one among many possible risk factors for development of Parkinson's disease.

Parkinson's disease affects nerve cells (neurons) in the part of the brain that controls muscle movement. People with Parkinson's disease often experience trembling, muscle rigidity, difficulty walking, and problems with balance and coordination. These symptoms generally develop after age 50, although the disease also affects a small percentage of younger people. The normal lifetime risk to develop Parkinson's disease for men and women combined is 1.7 percent.

Note: If no author is given, the source is cited instead.

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