Obesity May Enhance the Adverse Effects of NO2 Exposure in Urban Schools on Asthma Symptoms in Children

Abstract

To evaluate relationships between inner-city classroom NO2 exposure and asthma symptoms and morbidity by BMI category.Children aged 4 to 13 (n = 271) years from 37 inner-city schools who had physician-diagnosed asthma for at least 1 year and were using daily preventive asthma medication, had wheezing within the last year, and/or had at least 1 unscheduled health care visit for asthma within the past year.This was a single-center prospective study conducted within the School Inner-City Asthma Study. Before the start of the academic year, baseline demographics, environmental factors, and asthma symptoms and medication use were obtained by questionnaire. Baseline evaluations included skin testing to common seasonal and perennial aeroallergens or by assessment serum-specific IgE to the same allergens, spirometry, and fractional exhaled nitric oxide (FeNO) measurement. BMI percentile was calculated and categorized by using CDC classifications. Classroom NO2 was measured twice during the school year, ∼6 months apart. The primary outcome was the number of days with asthma symptoms within the previous 14 days. The secondary outcomes assessed in the previous 2 weeks were the number of exacerbations (hospitalizations or unscheduled health care visits for asthma), the number of days caretakers had to change plans because of the child’s asthma symptoms, FeNO level, and pulmonary function (forced expiratory volume in 1 second [FEV1] and forced vital capacity [FVC]).Participants were predominantly African American and Hispanic (35% each) and impoverished (49% had an annual household income <$25 000). A total of 50% had normal BMI (fifth percentile to <85th percentile), 15% were overweight (85th percentile to <95% percentile), and 35% were obese (≥95th percentile). Most (69%) were atopic, with specific immunoglobulin E to at least 1 aeroallergen. Obese students with asthma had statistically (but likely not clinically relevant) lower pulmonary function (FEV1 and FVC but not FEV1/FVC ratio), more positive skin test results, and lower FeNO than students with normal weight. The BMI category did not affect asthma symptom days, asthma symptoms, medication use, health care use for asthma, or missed school days. Caretakers of children with normal weight changed their plans more often than those of students who were overweight or obese. For children with normal weight or those who were overweight, NO2 levels were not associated with any of the measured outcomes. However, among children who were obese, for every 10-fold increase in NO2 level there were increased odds of asthma symptom days (1.9-fold), acute asthma-related health care use (2.4-fold), a missed school day because of asthma (3.1-fold), and care takers’ plans being changed because of the child’s asthma (4.2-fold). As compared with children with normal weight, in students who were obese, every 10 parts per billion increase in classroom NO2 level increased the likelihood of an asthma symptom day (odds ratio: 1.86; 95% confidence interval: 1.15 to 3.02) and of care takers changing their plans (odds ratio: 4.24; 95% confidence interval: 2.33 to 7.70). NO2 levels did not affect other outcomes, lung function, or FeNO across BMI categories.Obesity in inner-city students with asthma appears to increase susceptibility to the adverse effects of classroom NO2.NO2 is formed by combustion of liquid or solid fossil fuels. Indoor sources include gas stoves, heaters, and poorly ventilated furnaces and fireplaces. Furthermore, outdoor levels are elevated in heavily trafficked urban areas. The Environmental Protection Agency’s standard for safe outdoor level of NO2 is ∼50 parts per billion over a 1-year averaging time and 100 parts per billion over a 1 hour averaging time. Although the authors of this study do not specifically report classroom NO2 levels, it is clear from the 2 figures in the article that levels did not exceed 30 parts per billion, hence they were nowhere near the level up to which the Environmental Protection Agency considers safe. This is a warning that “safe” might not be safe enough. I think we all recognize the multiple and varied effects that both pollution and obesity have on health. With this study, the authors suggest synergy between 2 health risk factors and indicate that, as physicians, we must address all known risk factors for disease as we provide the best preventive and prospective care we can.