To the Editors:
In preschool children, exposure to traffic-related emissions is associated with increased prevalence of respiratory symptoms [1–3] and, in school-aged children, with reduced lung function growth [4]. However, to date, the association between air pollution and preschool lung function remains unclear. In a cross-sectional study, we investigated the effects of residential proximity to main roads and air pollutants on lung function in healthy preschool children.
Spirometric forced vital capacity, forced expiratory volume in 1 s and 0.5 s, lung clearance index (LCI) by multiple breath washout, plethysmographic specific airway resistance (sRaw) and exhaled nitric oxide fraction (FeNO) were measured in healthy preschool children as part of another study protocol [5]. Residential distance to the nearest main road was computed using Geographical Information System software (ArcGIS, ESRI, Redlands, CA, USA). An atmospheric dispersion model estimated the past 3 yrs exposure data for mean annual carbonaceous particulate matter with a 50% cut-off aerodynamic diameter of 10 μm (PM10), nitrogen dioxide (NO2) and nitrogen oxides (NOx). Statistical analysis was performed by Mann–Whitney U-tests, and simple and multiple linear regression analyses. Sample size was opportunistic and determined by the number of children recruited to the original study [5].
70 children, median (range) age 5.5 (4.1–6.9) yrs, were recruited (50% male) to the original study [5]. Spirometric measurements were successful in 55 children, LCI and sRaw in 70 children and FeNO in 65 children. While residential distance from main roads was computed for all 70 children, past 3 yrs mean annual air pollutants data could be estimated in 51 children living within Greater London, UK.
As expected, modelled exposure to air pollution was higher in children living within 150 m of a main road (table 1). There was no significant difference in any of the lung function variables or FeNO according to residential proximity to main roads (table 1). Simple and multiple linear regression analyses after adjusting for age, sex, height and atopy showed no significant associations between lung function parameters and FeNO with residential distance from main roads or mean 3 yr annual PM10, NO2 and NOx exposure.
In this cross-sectional study of healthy preschool children, we found no evidence of an association between living in proximity to a main road and lung function. It is possible that failure to show an association is related to inadequate power. However, we found no trends for reduced lung function in children living within 150 m of a main road. An alternative explanation is that decrements of lung growth are not the major drivers of air pollution triggered symptoms in young children who have had insufficient time for a cumulative effect of air pollution on lung function growth. In contrast, increased prevalence of clinically low lung function in adolescents living in areas of high air pollution reflects many years of a negative effect of air pollution on lung growth [4].
In conclusion, we have shown that lung function in a small cohort of healthy children at median age 5.5 yrs is not significantly affected by living in proximity to main roads with high traffic-related air pollutants. We therefore speculate that the association between air pollution and respiratory symptoms in preschool children is perhaps due to impaired pulmonary innate immunity as suggested by animal models and not impaired lung function per se [6].
Footnotes
Support Statement
This study was supported by Asthma UK, Smiths Medical and the European Respiratory Society.
Statement of Interest
A statement of interest for the study itself can be found at www.erj.ersjournals.com/site/misc/statements.xhtml
- ©ERS 2011