Obesity may enhance the adverse effects of NO2 exposure in urban schools on asthma symptoms in children

Abstract

Background: Sparse data address the effects of nitrogen dioxide (NO₂) exposure in inner-city schools on obese students with asthma.

Objective: We sought to evaluate relationships between classroom NO₂ exposure and asthma symptoms and morbidity by body mass index (BMI) category.

Methods: The School Inner-City Asthma Study enrolled students aged 4 to 13 years with asthma from 37 inner-city schools. Students had baseline determination of BMI percentile. Asthma symptoms, morbidity, pulmonary inflammation, and lung function were monitored throughout the subsequent academic year. Classroom NO₂ data, linked to enrolled students, were collected twice per year. We determined the relationship between classroom NO₂ levels and asthma outcomes by BMI stratification.

Results: A total of 271 predominantly black (35%) or Hispanic students (35%) were included in analyses. Fifty percent were normal weight (5-84th BMI percentile), 15% overweight (≥85-94th BMI percentile), and 35% obese (≥95th BMI percentile). For each 10-parts per billion increase in NO₂, obese students had a significant increase in the odds of having an asthma symptom day (odds ratio [OR], 1.86; 95% CI, 1.15-3.02) and in days caregiver changed plans (OR, 4.24; 95% CI, 2.33-7.70), which was significantly different than normal weight students who exhibited no relationship between NO₂ exposure and symptom days (OR, 0.90; 95% CI, 0.57-1.42; pairwise interaction P = .03) and change in caregiver plans (OR, 1.37; 95% CI, 0.67-2.82; pairwise interaction P = .02). Relationships between NO₂ levels and lung function and fractional exhaled nitric oxide did not differ by BMI category. If we applied a conservative Holm-Bonferroni correction for 16 comparisons (obese vs normal weight and overweight vs normal weight for 8 outcomes), these findings would not meet statistical significance (all P > .003).

Conclusions: Obese BMI status appears to increase susceptibility to classroom NO₂ exposure effects on asthma symptoms in inner-city children. Environmental interventions targeting indoor school NO₂ levels may improve asthma health for obese children. Although our findings would not remain statistically significant after adjustment for multiple comparisons, the large effect sizes warrant future study of the interaction of obesity and pollution in pediatric asthma.

Keywords: Asthma; BMI; NO(2); air; body mass index; children; environment; exposure; indoor; inner-city; nitrogen dioxide; obesity; pollutant; school; urban.

FIGURE 1.. Schematic diagram of SICAS procedures and assessments.

FIGURE 2.. Effect of BMI Status on the Association of Increasing Classroom NO2 Exposure and Asthma Symptom Days

The p value for pairwise interaction between obese and normal weight BMI effects is 0.03, see Table 2 statistics. All models adjusted for age, race, sex, baseline controller medication use, season, any sensitization, and environmental tobacco smoke exposure.

FIGURE 3.. Effect of BMI Status on the Association of Increasing Classroom NO2 Exposure and Change in Caregiver Plans

The p value for pairwise interaction between obese and normal weight BMI effects is 0.02. All models adjusted for age, race, sex, baseline controller medication use, season, any sensitization, and environmental tobacco smoke exposure.