Central obesity is the most critical determinant of obesity-related morbidity in many diseases. However, studies directly comparing obesity measures that assess central obesity with BMI measures are lacking in childhood asthma and allergic rhinitis. We directly compared obesity measures in children with allergic rhinitis with or without asthma. Our results demonstrate that measures that account for fat distribution and central obesity classify obesity differently than BMI. In fact, there was up to 46% discordance between BMI percentiles and the central obesity measures. Thus, a significant proportion of children with allergic rhinitis designated as obese or non-obese using BMI percentiles will be designated differently using alternative measures that account for central obesity. Furthermore, we observed a significant association of central obesity (assessed using conicity index) with having asthma and with more severe asthma. Although BMI percentiles were associated with asthma and asthma severity in Caucasians, the associations of central obesity measures with asthma were more consistent (even in mixed populations and in Caucasians), suggesting that central obesity may be superior to BMI percentiles in assessing the likelihood for having asthma in children with allergic rhinitis.
In contrast to asthma severity, a negative association was observed between obesity and allergic sensitization among asthmatics. Thus, allergic sensitization was less common among the obese subgroup. This finding was more pronounced with central obesity (assessed using waist circumference), and is supported by a study that found that central obesity was associated with non-atopic asthma in adults38
. This suggests that among obese children, there are factors that contribute to the development of asthma independent of allergic sensitization. This is an important and intriguing observation. Allergic sensitization still occurs in the context of obesity, but mechanisms other than allergic sensitization likely contribute to the link between obesity and asthma. The structural equation model further supported this observation, since none of the obesity measures were associated with atopy, despite the robust association of central obesity with asthma.
To date, the majority of the studies that support an association between asthma and obesity using measures that assess fat distribution have been performed in adults and have been mainly limited to Caucasians7, 38–40
. The study herein has several advantages. First, it was performed in Caucasian and African American children. In addition, the racial and socioeconomic makeup of the children participating in this study is similar to the national census figures (year 2000 figures, www.censusscope.org
). The only exception is a higher proportion of African Americans, which is not surprising since asthma disproportionately affects this subgroup. Second, weight and height were objectively measured. In previous studies that found an association between obesity with asthma, several used self-reported weight and height41, 42
, which is a potential source of error due to reporting bias. Third, the diagnosis of asthma was based on objective lung function criteria, while other studies have relied largely on self-reported asthma18, 41, 43
. Fourth, percentile curves were constructed for each obesity measure, providing race and gender-specific quantile reference values for this specific population. Finally, a structural equation model, examining the indirect effects of the obesity measures, confirmed the association of central obesity with asthma in all the children.
This study is not generalizable to the US population because it was performed in a clinic sample of children. Although the relationship between asthma and obesity, and specifically central obesity, is supported by our findings, no conclusions about causality can be made due to the cross-sectional design. Potential confounders that may impact the association between asthma and obesity include gastro-esophageal reflux disease and sleep disordered breathing. Neither of these was assessed in this study. However, gastro-esophageal reflux disease did not have an effect on the association between asthma and obesity in a longitudinal study49
. Similarly, sleep disordered breathing based on sleep apnea or habitual snoring did not alter the association between obesity and asthma50
Given the burden of childhood obesity, these results have public health relevance. Based on these data, measures of central obesity should be incorporated in pediatric and allergy/immunology practices in order to better identify patients with allergic rhinitis who may be at increased risk for asthma due to co-morbid obesity.