As anyone with seasonal allergies to tree pollen knows, allergy season has begun. Aside from the sneezing, itchy eyes, nasal congestion, and general sense of being ill, is there anything good about this springtime immune system dysfunction? I came across some evidence that might slightly relieve that annual sense of “suffering” – having allergies of any kind seems to reduce the risk of glioma, including malignant brain tumors, by up to 40%.
Asthma, eczema, and hay fever seem to all have this “protective” effect. Multiple observational, case-control studies have shown that allergic conditions are associated with a lower risk of glioma, and this has been confirmed by a larger, systematic meta-analysis. One prospective study found a 25% lower risk of gliomas in subjects with high IgE levels. When women alone were analyzed, those with the highest IgE levels had up to a 50% reduced risk of gliomas. IgE is the type of antibody most often found abnormally high in those with allergic/atopic conditions. It is not known why women seems to have greater protection than men.
It is postulated that a general immune system activation with heightened immune surveillance explains this cancer reduction phenomenon among those with allergies. An activated, vigilant immune system may destroy central nervous system cancer cells.
Ironically, the most common treatments for allergies, antihistamines, contain precursors of n-nitroso compounds which have been found to be potent neurocarcinogens. Some think these chemicals, which are also found in cured meats and bacon, may increase the risk of brain cancer by 2-3 fold. More recent studies, however, have been done prospectively and show no clear association between n-nitroso compounds and glioma.
And so while the nuisance of allergies as a medical problem cannot be compared with the profound suffering of those with malignant brain tumors, it seems as though all the sniffles, wheezes, and congestion may have at least one potential benefit.