Individuals living closer to the equator are at an increased risk for hay fever, food allergy, and skin sensitization to house dust mites (HDM) and molds, research shows.
In the study, both living closer to the equator and higher UV-B exposure were also associated with an increased risk for current asthma among atopic individuals and a reduced risk for current asthma among non-atopic individuals.
"We found that latitude and UV-B exposure were associated with current asthma and that atopy modified those associations but asthma severity did not," report Shyamali Dharmage (University of Melbourne, Australia) and colleagues.
Writing in the Annals of Allergy, Asthma, and Immunology, the researchers say their findings suggest that geographic factors "may have a role in the development of asthma and allergic disease."
The group analyzed data from 5729 participants in the Tasmanian Longitudinal Health Study, a population-based study of respiratory disease spanning childhood to adulthood.
In the most northerly latitude, that being closest to the equator, individuals had a significant 28% increased risk for hay fever, a significant 34% increased risk for food allergy, and a significant 41% increased risk for dust allergy compared with those in the most southerly.
Similarly, individuals living in the most northerly latitude had a significant twofold increased risk for skin sensitization to HDM. They also had a significant twofold increased risk for sensitization to Alternaria and a fivefold increased risk for sensitization to Aspergillus.
Cumulative UV-B exposure was associated with a sensitization to HDM and Aspergillus, but the association was not statistically significant.
In an analysis of individuals by atopic status, the researchers observed that atopic individuals living in the most northerly latitude had a 51% increased risk for current asthma. By contrast, non-atopic individuals in the most northerly latitude had a 74% reduced risk for current asthma.
Higher cumulative UV-B status in atopic individuals in the most northerly latitude was associated with a 90% higher risk for current asthma, whereas there was a trend toward a lower risk among non-atopic individuals.
"The finding of a differential effect of atopy on the relationship between latitude or UV-B exposure and asthma has not been reported previously," according to Dharmage and colleagues.
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