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21 August 2012
The link between your seasonal runny nose and a potential cancer in your brain may not be immediately obvious but there is one. For some time researchers have believed that having allergies reduces the risk for a type of brain cancer known as glioma. Now a new study has confirmed that this is the case.
Glial cells make up the supportive tissue of the brain and, unlike neurons, don’t conduct electrical impulses. The glial cells include astrocytes, oligodendrocytes, and ependymal cells, each with specialised functions. Astrocytes regulate brain activity and control the movement of blood to the brain. They are star-shaped, hence their name ‘astro’. Oligodendrocytes produce the myelin sheath that surrounds the nerve fibres in the brain and spinal cord, and helps conduct messages along the nerves. Ependymal cells line the internal (ventricular) walls of the fluid spaces located inside the brain canal and spinal cord. Glioma is a cancer of any of these cells and it affects around three in 100,000 people.
Around 25 to 30 per cent of all gliomas involve the astrocytes while 35 to 40 per cent involve oligodendrocytes. If left untreated, any type of glioma may grow and press on other structures within the brain. Pressure on the brain can be harmful as it forces the brain against the skull, causing damage to the brain and hampering its ability to function properly. This reduced function can lead to long-lasting brain damage or, if left untreated, death.
There is however, an interesting aspect to gliomas; researchers have observed that having an allergy reduces your risk for developing glioma. The question has been whether gliomas somehow suppress allergies or do allergies somehow suppress glioma risk? This is what a new study sought to examine.
To do this the researchers examined stored blood samples from the Janus Serum Bank in Norway which contains samples of people who had annual medical check-ups over the last 40 years. Since 1953 Norway has also registered all cancer cases recorded in the country and personal ID numbers allow cross-referencing with blood samples. The researchers analysed samples from 594 people diagnosed with glioma between 1974 and 2007 and compared them to 1,777 samples from people who did not develop glioma.
The analysis showed that men and women with allergy had a 25 per cent reduction in their risk of developing glioma in the next 20 years. The interesting thing was that the effect seemed to be time specific. There was a 46 per cent reduction in risk for developing glioma 20 years later but the risk was only reduced by about 25 per cent for those with high levels of IgE taken between two and fifteen years before diagnosis. This suggests that it is the allergy that reduces cancer risk and not the other way around. Allergy was measured by levels of IgE (immunoglobulin E) in the blood. IgE is the part of the immune system that identifies specific components of an allergy causing substance. It might be that high circulating levels of these antibodies in the blood of allergic people somehow lowers the risk of glioma by stimulating the immune system.
No-one is suggesting that inducing allergy should be contemplated as a way to avoid the relatively low risk of developing a cancer. It does however take us a step closer to understanding cancer development and for allergy sufferers it is a silver lining that is not to be sneezed at.