PURPOSE OF THE STUDY.
To examine the association of obesity and fitness on risk of asthma in adolescent girls and boys.
Cross-sectional analysis of data of 4828 subjects, 12–19 years old, from the 1999–2004 NHANES. Mean age of males was 15.5 years and mean age of females was 15.3 years.
Data including cardiorespiratory fitness testing (submaximal treadmill exercise test), body composition measurements, and respiratory questionnaires from NHANES were used. Asthmatics were defined as those who responded “yes” when asked whether a doctor or health professional had told them they had asthma. Participants were classified as normal weight if sex-specific BMI percentile-for-age was fifth to <85th, overweight if 85th to <95th, and obese if ≥95th. Comparisons of subjects’ characteristics were done for continuous variables with an independent sample t test and for categorical variables with a Pearson χ2 test; then, sex-specific associations of BMI and fitness with prevalence and morbidity were analyzed with logistic regression models, stratified by sex.
In females, being overweight or obese was associated with increased odds of history of or current asthma (aOR 1.63, 95% CI 1.16–2.3; aOR 1.73, 95% CI 1.13–2.64) in addition to asthma attacks (aOR 2.67, 95% CI 1.56–4.65) and exercise-related wheezing (aOR 1.6, 95% CI 1.07–2.38). This association was not seen in males. In males, there was an association between high fitness and lower odds of asthma-related visits to the emergency department (aOR 0.24, 95% CI 0.07–0.89), wheezing-related medical visits (aOR 0.31, 95% CI 0.13–0.75), wheezing-related missed days (aOR 0.14, 95% CI 0.06–0.33), and exercise-related wheezing (aOR 0.43, 95% CI 0.06–0.33), but this was not observed in females.
This study found that, in adolescent females, there is an association between overweight/obesity and increased asthma prevalence and morbidity, independent of fitness. In adolescent males, there is an association between high fitness and decreased rates of asthma morbidity that is independent of weight categorization. This suggests that the prevalence and morbidity of asthma are affected differently in adolescent females as compared with adolescent males.
It has been suggested before that there are gender differences in the effects of obesity on prevalence and morbidity of asthma, though there are few studies examining an adolescent population or that also consider fitness. As the authors noted, there is insufficient evidence to conclude that the observed differences were true as opposed to simply by chance. However, others have also noted this relationship between obesity and asthma in females, though it is unclear why this may be. More females reported wheezing related to exercise, which begs the question of directionality. Furthermore, if obesity is related to the development of and morbidity associated with asthma in females, there are likely a multitude of players in this complex relationship, including hormones, puberty, adipokines, adipose distribution, and inflammation, whose potential roles have yet to be elucidated. Nevertheless, the mechanisms in which obesity may predispose females to asthma and associated morbidity and, conversely, those related to high fitness that potentially protect males are currently unknown, and the potential of a biological mechanism based on the results of this study highlights the need for further research.
- Copyright © 2017 by the American Academy of Pediatrics