Urban–rural differences in asthma prevalence among young people in Canada: the roles of health behaviors and obesity Joshua A. Lawson, PhD*; Ian Janssen, PhD†; Mark W. Bruner, PhD‡; Koroush Madani, MPH§; and William Pickett, PhD¶ Background: Asthma prevalence has been reported to be lower in rural regions, but the reasons for this are not known. Objective: To confirm the existence of an urban–rural geographic gradient in asthma prevalence among Canadian youths and to evaluate whether this gradient was mediated by health behaviors. Methods: Cross-sectional data from 4,726 Canadian youth (grades 6 –10) were collected during the 2001– 02 Health Behaviour in School-Aged Children survey. Geographic region was categorized as metro (urbanized), non-metro but adjacent to metro, and rural. Asthma was defined via self-report of doctors’ diagnoses and at least 1 of: (1) asthma symptoms or (2) a health care visit for asthma in the past year. Health behaviors (diet and physical activity) as well as obesity were also assessed. Results: Asthma prevalence was lowest in rural regions (metro = 17.7%, non-metro-adjacent = 15.6%, rural = 14.8%). A lower risk of asthma was associated with rural region (adjusted odds ratio [OR] = 0.76, 95% CI = 0.61– 0.95) and living in non-metro- adjacent regions (adjusted OR = 0.81, 95% CI = 0.65–1.01). Health behaviors and obesity status did not mediate the association between geographic region and asthma. Being overweight or obese, having a high physical activity level, and exposure to passive smoking independently elevated the risk of asthma, whereas increased consumption of whole milk or vegetables were each protective. Conclusions: Although asthma prevalence among youth was lower in rural areas, this association was not mediated by health behaviors or obesity. Other exposures, likely environmental, are the logical mechanisms through which rural geographic status is related to lower asthma prevalence. Ann Allergy Asthma Immunol. 2011;107:220 –228. INTRODUCTION Asthma conveys a large impact on the people affected by the disease and on society, especially pediatric populations. Quality of life is lower among children with asthma, 1 and asthma is resource intensive, because it results in a large amount of health care utilization. 2 Asthma has become quite common in children, but the prevalence has been shown to vary geographically. 3,4 A lower prevalence of childhood asthma has been associated with rural residence, 5 but the reasons remain unknown. Explanations could include differ- ences in diagnostic patterns and access to health care, varia- tions in exposures to environmental factors, and differences in body mass index (BMI) status and health behaviors. How- ever, little research is available that identifies which of these explanations is most plausible. Among the proposed explanations, urban–rural differences in health behaviors and obesity provide a logical explanation that accounts for the observed geographic gradients in the prevalence of asthma. Obesity status and health behaviors, such as physical activity and smoking, are associated with asthma in young people 6 –14 and are known to vary across urban and rural populations. 15–17 Consequently, these factors could be a mechanism by which the association between geographic location and asthma is occurring. Understanding the association between urban–rural status and asthma will help identify factors contributing to varia- tions in asthma prevalence. If an explanation for the urban– rural differences in asthma prevalence can be identified, by Affiliations: * Canadian Centre for Health and Safety in Agriculture, University of Saskatchewan, Saskatoon, SK, Canada, and the Department of Medicine, University of Saskatchewan, Saskatoon, SK, Canada; † School of Kinesiology and Health Studies, Queen’s University, Kingston, ON, Canada, and the Department of Community Health and Epidemiology, Queen’s University, Kingston, ON, Canada; ‡ School of Physical and Health Educa- tion, Nipissing University, North Bay, ON, Canada; § Department of Com- munity Health and Epidemiology, University of Saskatchewan, Saskatoon, SK, Canada; ¶ Department of Community Health and Epidemiology, Queen’s University, Kingston, ON, Canada, and the Department of Emer- gency Medicine, Queen’s University, Kingston, ON, Canada. Disclosures: Authors have nothing to disclose. Funding Sources: Pilot project funding from the Canadian Centre for Health and Safety in Agricultural with program funding from the Canadian Institutes of Health Research. The Canadian version of the World Health Organization- Health Behaviour in School-Aged Children Survey (WHOHBSC) was sup- ported by research agreements with the Public Health Agency of Canada (contract: HT089-05205/001/SS). The WHO-HBSC is a WHO/Euro collabora- tive study. International Coordinator of the 2001-02 study: Candace Currie, University of Edinburgh, Scotland; and Data Bank Manager: Oddrun Samdal, University of Bergen, Norway. This publication reports data solely from Canada (Principal Investigator in 2001/02: William Boyce). The study reported herein was supported by a pilot grant from the Canadian Institutes of Health Research program funding the Canadian Centre for Health and Safety in Agriculture projects. I.J. holds a Canada Research Chair in Physical Activity and Obesity, and was supported by investigator awards from the Canadian Institutes of Health Research and the Ontario Ministry of Research and Innovation. Received for publication April 17, 2011; Received in revised form May 31, 2011; Accepted for publication June 18, 2011. © 2011 American College of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.anai.2011.06.014 220 ANNALS OF ALLERGY, ASTHMA & IMMUNOLOGY