Effect of Early Life Exposure to Air Pollution on Development of Childhood Asthma
Clark, Nina Annika, Demers, Paul A., Karr, Catherine J., Koehoorn, Mieke, Lencar, Cornel, Tamburic, Lillian, Brauer, Michael, Environmental Health Perspectives
BACKGROUND: There is increasing recognition of the importance of early environmental exposures in the development of childhood asthma. Outdoor air pollution is a recognized asthma trigger, but it is unclear whether exposure influences incident disease. We investigated the effect of exposure to ambient air pollution in utero and during the first year of life on risk of subsequent asthma diagnosis in a population-based nested case-control study.
METHODS: We assessed all children born in southwestern British Columbia in 1999 and 2000 (n = 37,401) for incidence of asthma diagnosis up to 3--4 years of age using outpatient and hospitalization records. Asthma cases were age-and sex-matched to five randomly chosen controls from the eligible cohort. We estimated each individual's exposure to ambient air pollution for the gestational period and first year of life using high-resolution pollution surfaces derived from regulatory monitoring data as well as land use regression models adjusted for temporal variation. We used logistic regression analyses to estimate effects of carbon monoxide, nitric oxide, nitrogen dioxide, particulate matter [less than or equal to] 10 [micro]m and [less than or equal to] 2.5 [micro]m in aerodynamic diameter ([PM.sub.10] and [PM.sub.2.5]), ozone, sulfur dioxide, black carbon, woodsmoke, and proximity to roads and point sources on asthma diagnosis.
RESULTS: A total of 3,482 children (9%) were classified as asthma cases. We observed a statistically significantly increased risk of asthma diagnosis with increased early life exposure to CO, NO, [NO.sub.2], [PM.sub.10], [SO.sub.2], and black carbon and proximity to point sources. Traffic-related pollutants were associated with the highest risks: adjusted odds ratio = 1.08 (95% confidence interval, 1.04-1.12) for a 10-[micro]g/[m.sup.3] increase of NO, 1.12 (1.07-1.17) for a 10-[micro]g/[m.sup.3] increase in [NO.sub.2] and 1.10 (1.06-1.13) for a 100-[micro]g/[m.sup.3] increase in CO. These data support the hypothesis that early childhood exposure to air pollutants plays a role in development of asthma.
KEY WORDS: administrative data, air pollution, asthma, children's health, in utero, respiratory, traffic. Environ Health Perspect 118:284-290 (2010). doi:10.1289/ehp.09009l6 available via http://ax.doi.org/ [Online 8 October 2009]
Asthma is the most common chronic disease in childhood [World Health Organization (WHO) 2006]. Its prevalence is high and has generally increased worldwide over the latter part of the 20th century (Asher et al. 2006; WHO 2006). Although explanations for relatively rapid changes in prevalence are unknown, environmental factors, independently and jointly with genetic factors, are thought to be responsible. Although air pollution has been consistently shown to exacerbate existing asthma (English et al. 1999; Lipsett et al. 1997; McConnell et al. 1999, 2006; Nicolai et al. 2003; Norris et al. 1999), there are few investigations of asthma onset and air pollution despite the hypothesized link with exposure to outdoor air pollution (Institute of Medicine 2000; von Mutius 2000).
Earlier studies have generally relied on simple measures of traffic proximity and density to estimate exposure and have not found an association between air pollution and asthma incidence (Ciccone et al. 1998; English et al. 1999; Wjst et al. 1993). More recent studies have used modeling approaches that provide high-resolution estimates of neighborhood-scale variations in air pollution. Several studies using this approach have observed increases in asthma incidence or asthma symptoms for children exposed to higher levels of traffic-related air pollution (Brauer et al. 2002, 2007; Gauderman et al. 2005; McConnell et al. 2006; Morgenstern et al. 2008; Zmirou et al. 2004). However, not all such studies of this type have reported consistent associations (Gehring et al. 2002; Zmirou et al. 2004).
Pre- and postbirth exposures to environmental tobacco smoke (ETS) are independently associated with increased asthma incidence (Haberg et al. …