Gender differences in effects of obesity and asthma on adolescent lung function: Results from a population-based study

Objective: To investigate lung function associated with asthma and body mass index (BMI) among adolescents at 96 northern Taiwan junior high schools participating in an asthma screening program. Methods: The questionnaires and lung function test results measured for 3669 boys and 3523 girls were included in this study for data analysis. Measures of forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1) and FEV1/FVC ratio were compared by sex, asthma status and BMI. Results: Overall mean FVC levels were similar between students with and without asthma, 3.71 L vs. 3.71 L for boys (p = 0.991) and 2.79 vs. 2.78 for girls (p = 0.517). The overall mean FEV1 levels were also similar between girls with and without asthma. Asthmatic boys had lower FEV1 than non-asthmatic boys. Mean FEV1/FVC was significantly lower in students with asthma than those without asthma. Mean FVC and FEV1 increased with BMI in both sexes. A lower mean FEV1/FVC was observed among students with asthma and high BMI, and was more pronounced in boys than in girls. Multivariable regression analysis also showed that FEV1/FVC ratios were negatively associated with asthma and high BMI, stronger in boys than in girls for asthma (β = −2.176 (standard errors (SE) = 0.268) vs. −1.085 (SE = 0.258) and for BMI (β = −0.309 (SE = 0.025) vs. −0.218 (SE = 0.029)). Conclusion: This northern Taiwan study suggests that FEV1/FVC is negatively associated with asthma and high BMI in adolescents, stronger for boys than for girls.