Original article
Systemic allergic disorder
Association between latitude and allergic diseases: a longitudinal study from childhood to middle-age

https://doi.org/10.1016/j.anai.2012.11.005Get rights and content

Abstract

Background

Worldwide variations in allergy prevalence suggest that geographic factors may contribute to asthma. Ecologic studies have suggested that latitude, a marker of UV-B exposure and allergen exposures, may be related to clinical allergies.

Objective

To examine the relationship between latitude or UV-B based on self-reported geolocation and allergic sensitization and disease prevalence in Australia.

Methods

The Tasmanian Longitudinal Health Study is a population-based study of respiratory disease spanning childhood to adulthood. The most recent follow-up included a postal survey of 5,729 participants and a clinical substudy of 1,396 participants. Participants' residential addresses were coded for latitude and linked with the UV-B data from satellite-based observations of atmospheric ozone. Multivariable logistic regression analyses were performed to estimate the associations between latitude or UV-B and allergic diseases.

Results

Most northerly latitude, that is, latitude closest to the Equator, and high current UV-B exposure were associated with increased odds of hay fever, food allergy, and skin sensitization to house dust mites and molds. More northerly latitude and higher UV-B exposure were associated with increased odds of current asthma among atopic individuals contrasting with a reduced odds of current asthma among nonatopic individuals.

Conclusion

This is the first study, to our knowledge, to demonstrate a differential effect of atopic status on the relationship between latitude and current asthma. Our study demonstrates in a genetically and culturally similar group of individuals that geographic factors may a play role in the development of allergic disease.

Introduction

Associations have been described between latitude and allergic diseases.[1], [2], [3], [4] In most studies, latitude was considered a marker for UV-B radiation exposure, which is linked to levels of vitamin D, a factor thought to modify the immune system toward a TH2 bias and an increased risk of allergy.[5], [6], [7], [8] Alternatively, latitude might simply reflect variation in aeroallergens due to climate, housing, social, and cultural differences.[9], [10]

Whether an increase in latitude is a risk or protective factor for allergy has not been established. Ecologic studies correlating latitude and surrogate measures of food allergy found a higher prevalence of infant hypoallergenic formula use and adrenaline prescriptions in the southern, less sunny part of Australia,[1], [2] whereas other international ecologic studies highlighted a higher prevalence of hay fever and asthma in equatorial areas.[3], [4] In contrast, a cross-sectional study reported no association between participants' residential latitudes, UV-B exposure, and vitamin D levels and asthma.11

To address these inconsistencies, we examined the relationship between latitude and allergic disease using data from the Tasmanian Longitudinal Health Study (TAHS). We used each participant's current residential location at the most recent TAHS follow-up survey and their yearly residential location in the previous 20 years to assign latitude exposure. We used self-reported allergy and results of skin prick tests (SPTs) to a panel of common aeroallergens.

Section snippets

Study Sample and Population

The sample was drawn from the fifth decade follow-up survey of TAHS, commencing in 2004. This included a postal survey, followed by a laboratory study of a subgroup of the respondents to the postal survey. Briefly, the TAHS started in 1968 when almost all 7-year-old children attending school in Tasmania (n = 8,583) were enrolled in a respiratory health study. Their parents completed a questionnaire concerning each child's respiratory symptoms, and the child underwent a clinical examination and

Participant Characteristics

Participants in the postal and laboratory surveys were similar with respect to sex and smoking status. As expected, those who participated in the laboratory study were more likely to have childhood (Table 1) and current asthma, as well as other allergies, than those only in the postal survey.

Self-reported Allergic Disease and Current Latitude–UV-B

The most northerly quartile for latitude, that is, closest to the equator, and the high quartile for current UV-B exposure were significantly associated with the highest odds of hay fever, food, and dust

Discussion

This is one of the few studies to date using individual latitude and UV-B exposure levels to examine their association with asthma and allergy and the first study, to our knowledge, to examine how these associations might vary with atopy. We found that latitude and UV-B exposure were associated with current asthma and that atopy modified those associations but asthma severity did not. Among atopic persons, proximity to the Equator and high UV-B exposure increased the odds of current asthma, but

Conclusion

This is the first study, to our knowledge, to demonstrate a differential effect of atopic status on the relationship between latitude and current asthma. Our study demonstrates in a large population-based cohort of genetically and culturally similar individuals that geographic factors may have a role in the development of asthma and allergic disease.

Acknowledgment

We acknowledge the study participants and previous investigators. We thank 6 current TAHS investigators who are not coauthors of this article (Dr James Markos, Associate Professor Paul Thomas, Associate Professor Mark Jenkins, Professor John Hopper, Professor Richard Wood-Baker, and Dr Iain Feather) for their assistance with obtaining funds and data collection. We also acknowledge Ms Cathryn Wharton and Dr Desiree Mészáros for coordinating the study and all the respiratory scientists who

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    Disclosures: Authors have nothing to disclose.

    Funding Sources: 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, The Asthma Foundation of Victorian, and Asthma Foundation of Tasmania. Drs Matheson, Dharmage, and Walters are supported by the National Health and Medical Research Council.

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