Living near the equator, where medium-wave ultraviolet light (UV-B) exposure is high, may increase the odds of developing allergy and, for people who are genetically predisposed, asthma, according to an article published in the February issue of the Annals of Allergy, Asthma & Immunology.
Vicka Oktaria, MPH, from the Centre for Molecular, Environmental, Genetic and Analytical Epidemiology, School of Population Health, University of Melbourne, Australia, and colleagues analyzed data from the Tasmanian Longitudinal Health Study (TAHS) to investigate whether a relationship existed between latitude of residence and UV-B exposure and allergic sensitization. Their analysis covered 5729 participants who responded to a 2004 respiratory questionnaire and a subgroup of 1397 of those participants who underwent clinical testing.
The researchers found that living closest to the equator and having high UV-B exposure were associated with greater odds of having hay fever and food allergy, in addition to skin sensitization to dust mites and mold. For instance, participants living in the most northerly quartile for latitude had an odds ratio (OR) of 1.41 (95% confidence interval [CI], 1.14 - 1.74; P = .002) for dust allergy and an OR of 5.03 (95% CI, 2.10 - 12.0; P < .001) for the prevalence of sensitivity to Aspergillus mold compared with participants living in the most southerly quartile.
The researchers also found an association between latitude and UV-B exposure, with greater odds of atopic individuals having asthma and decreased odds of nonatopic individuals having asthma.
In reaching these associations, the researchers used multivariate logistic regression models adjusting for confounders including sex, childhood asthma and eczema, parental allergy, socioeconomic status, and smoking. They also took into consideration the month of laboratory visits and location altitudes.
"This is the first study, to our knowledge, to demonstrate a differential effect of atopic status on the relationship between latitude and current asthma," the researchers write. "Our study demonstrates in a genetically and culturally similar group of individuals that geographic factors may play a role in the development of allergic disease."
The reason for the associations may be greater synthesis of vitamin D from high sun exposure. "UV-B...exposure is higher for people living in areas closer to the equator," Dr. Oktaria stated in a news release. "This increase in UV-B may be linked to vitamin D, which is thought to modify the immune system. These modifications can lead to an elevated risk of developing allergy and asthma."
One limitation of the study, the researchers write, was the inability to investigate other possible environmental considerations, such as temperature and rainfall, which were not collected as part of the data.
Collection of information in the TAHS began in 1968, when researchers enrolled almost all 7-year-old school children (n = 8583) in Tasmania. Data for the current study came from the fifth-decade follow-up survey, in which 7312 of the original enrollees were traced to an address in 2004.
This study was funded by the National Health and Medical Research Council of Australia, LEW Carty Charitable Fund, Clifford Craig Medical Research Trust of Tasmania, Asthma Foundation of Victorian, and Asthma Foundation of Tasmania. Three coauthors are supported by the National Health and Medical Research Council. The other authors have disclosed no relevant financial relationships.
Ann Allergy Asthma Immunol. 2013;110:80-85.e1. Abstract
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Cite this: High UV-B Exposure May Increase Allergy, Asthma Risks - Medscape - Feb 05, 2013.