There's strong evidence to suggest your aversion to dust, pollen, mold, and pets may be protecting you from brain cancer.

PROBLEM: Scientists have long suspected that there's an association between allergies and gliomas, a common and often fatal type of brain tumor. Studies had been done suggesting that people with allergies were less susceptible to the tumors, but they were all based on patients self-reporting whether or not they had allergies -- not on actual blood test evidence of allergy-related immune system variations. And because brain tumors themselves can weaken the immune system, including the immune response to allergens, it's been difficult to prove which condition came first.

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METHODOLOGY: In Norway, blood samples from annual check-ups and voluntary donations are saved and labeled with personal identification numbers. Thanks to this extremely organized and comprehensive system, researchers were able to obtain access to blood samples taken from 594 current glioma patients decades before they were diagnosed. They were also able to match them with samples from people who never developed glioma. In each sample, they measured the levels of two types of IgE, a protein that plays an essential role in allergic reactions. Then, they used statistical analysis to see whether elevated levels of IgE were associated with a reduced risk of developing a glioma.

RESULTS: People who tested positive for allergy-related antibodies had an almost 50 percent lower risk of developing a glioma 20 years later. For women, testing positive for the IgE associated with specific allergens that are common in Norway, such as dust, pollen, mold and pets, was also associated with a 50 percent lower risk of glioblastoma. In men, no such association was found, but those who tested positive both for these specific antibodies and for other, unknown antibodies did have a 20 percent lower risk of developing this same type of tumor. The earlier IgE was present in patients' blood samples, the greater the reduced risk of glioma.

CONCLUSION: The link between allergies and reduced risk of glioma is measurable and possibly causal, especially for women, and can be observed at least 20 years before diagnosis.

The full study, " Association Between Prediagnostic IgE Levels and Risk of Glioma" is published in the Journal of the National Cancer Institute.