However, the study didn't specify exactly how much more likely it is that an allergy-free person will develop a glioma compared to someone who has allergies.
What might allergies -- or the lack of them -- have to do with brain tumors? McCarthy said overactive immune systems may cause allergies and also allow people to fight off cancer. Figuring out what to do about this is the tough question.
"Obviously, it's not like allergies are a modifiable risk factor," she said. "You can't tell people to go out and develop allergies. That's not going to happen. And you can't tell people with allergies that, 'You're doing a good thing, and don't try to get rid of them.'"
The study doesn't prove a cause and effect -- that allergies directly lower the risk of brain tumor. It only shows a possible connection, one that doesn't sway Dr. Eugene S. Flamm, chairman of the department of neurosurgery at Montefiore Medical Center in New York City.
Flamm said the study is small and draws conclusions "far beyond the observational data."
"As the authors point out, there are several conflicting reports in the literature, and this paper does not resolve the issue in any way," Flamm said.
One reason for the conflicting reports, the authors said, was that "allergy" was defined differently in various studies -- sometimes broadly and sometimes narrowly, as in seasonal allergies alone. Further studies are essential, they said.
For more about brain cancer, visit the U.S. National Library of Medicine.
SOURCES: Bridget J. McCarthy, Ph.D., research associate professor of epi
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