It’s not often that having multiple allergies is a good thing, but that certainly seems to be the case if a recent study published in Cancer, Epidemiology, Biomarkers and Prevention is accurate. I was tempted to create a new category for ‘wacky findings’ but managed to resist the temptation, at least for now.
Self-reported data on medically diagnosed allergies and antihistamine use for patients with glioma (n=419) and cancer-free patients (n=692) was studied by researchers at the University of Chicago. The controls had no prior history of brain tumours or any other cancers, and did not have a history of neurodegenerative disease.
Respondents completed a web-based or telephone survey and were asked if they were medically diagnosed with allergies or asthma at least two years prior to the survey, and if so, the age of diagnosis. In addition, they were also asked to indicate the number of individual allergies within each of the following categories:
Details on regular medication usage two years or more prior to the survey, and information on specific medication brands, frequency and duration of usage were also collected.
What did they find?
- Allergies appeared to be protective, providing a reduced risk for those with who have a higher number and more types of allergies.
- Age of allergy diagnosis and years since diagnosis were not associated with glioma risk.
- Antihistamine use, including diphenhydramine hydrochloride (a possible neurocarcinogen), did not appear to affect glioma risk separately from the effects of allergies.
In essence, the study suggests that there is a relationship between the immune system of allergy sufferers and glioma risk.
However, if you look at the literature, the answer is not as clear cut as the researchers themselves point out:
“Allergies and/or atopic disease, on the other hand, have been associated with a significantly decreased risk of glioma in many, but not all, studies. The decreased risk associated with glioma has been hypothesized to be the result of an increase in immune surveillance related to atopic disease; this hyperactive immune surveillance may limit abnormal cell growth. However, the specific mechanism through which atopic disease may influence glioma risk has not been identified and noncausal associations with glioma risk have not been ruled out.”
They also went on to suggest that:
“A comprehensive study of allergies and antihistamine use using standardized questions and biological markers will be essential to further delineate the biological mechanism that may be involved in brain tumor development.”
To circle back to the original question…
Many of you will be very aware that discovering a relationship occurs between two variables does not imply causality, so until the mechanism of action for this phenomenon is delineated one way or the other, I would treat the results with a rather large pinch of salt.
McCarthy, B., Rankin, K., Il’yasova, D., Erdal, S., Vick, N., Ali-Osman, F., Bigner, D., & Davis, F. (2011). Assessment of Type of Allergy and Antihistamine Use in the Development of Glioma Cancer Epidemiology Biomarkers & Prevention, 20 (2), 370-378 DOI: 10.1158/1055-9965.EPI-10-0948