Here's an interesting potential risk factor for allergies and asthma: your proximity to the Equator.
A new study in the journal Annals of Allergy, Asthma & Immunology shows that people who live closer to the Equator and who are exposed to high levels of UV-B radiation have a higher risk of allergies and asthma, compared to people who live further away from the equator.
Researchers examined data from the Tasmanian Longitudinal Health Study, which included respiratory disease rates of 5,728 people, as well as a clinical sub-study of 1,392 people. They found that those who lived in the northernmost latitude (closet to the Equator) were the most sensitive to hoist dust mites and mold, and were more likely to have food allergies or hay fever. People who lived closest to the Equator and who were exposed ot the most UVB radiation also had higher odds of having asthma.
The association between UVB radiation exposure and asthma risk "may be linked to vitamin D, which is thought to modify the immune system," study researcher Vicka Oktaria, MPH, of the University of Melbourne in Australia, explained in a statement. "These modifications can lead to an elevated risk of developing allergy and asthma."
This isn't the first time an association has been drawn between distance to the Equator, UV radiation and allergy/asthma risk. In 2011, another study conducted by Australian researchers also showed a link between distance to the Equator and increased asthma risk (though researchers said that once daily temperature was taken into account, this was no longer evident), as well as exposure to sun during the winter time and increased odds of having hay fever.