Articles
Exposure to air pollution and development of asthma and rhinoconjunctivitis throughout childhood and adolescence: a population-based birth cohort study

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Summary

Background

Previous published analyses have focused on the effect of air pollution on asthma and rhinoconjunctivitis throughout early and middle childhood. However, the role of exposure to air pollution in the development of childhood and adolescent asthma and rhinoconjunctivitis remains unclear. We aimed to assess the longitudinal associations between exposure to air pollution and development of asthma and rhinoconjunctivitis throughout childhood and adolescence.

Methods

We did a population-based birth cohort study of 14 126 participants from four prospective birth cohort studies from Germany, Sweden, and the Netherlands with 14–16 years of follow-up. We linked repeated questionnaire reports of asthma and rhinoconjunctivitis with annual average air pollution concentrations (nitrogen dioxide [NO2], particulate matter [PM] with a diameter of less than 2·5 μm [PM2·5], less than 10 μm [PM10], and between 2·5 μm and 10 μm [PMcoarse], and PM2·5 absorbance [indicator of soot]) at the participants' home addresses. We analysed longitudinal associations of air pollution exposure at participants' birth addresses and addresses at the time of follow-up with asthma and rhinoconjunctivitis incidence and prevalence in cohort-specific analyses, with subsequent meta-analysis and pooled analyses.

Findings

Overall, the risk of incident asthma up to age 14–16 years increased with increasing exposure to NO2 (adjusted meta-analysis odds ratio [OR] 1·13 per 10 μg/m3 [95% CI 1·02–1·25]) and PM2·5 absorbance (1·29 per 1 unit [1·00–1·66]) at the birth address. A similar, albeit non-significant, trend was shown for PM2·5 and incident asthma (meta-analysis OR 1·25 per 5 μg/m3 [95% CI 0·94–1·66]). These associations with asthma were more consistent after age 4 years than before that age. There was no indication of an adverse effect of air pollution on rhinoconjunctivitis.

Interpretation

Exposure to air pollution early in life might contribute to the development of asthma throughout childhood and adolescence, particularly after age 4 years, when asthma can be more reliably diagnosed. Reductions in levels of air pollution could help to prevent the development of asthma in children.

Funding

The European Union.

Introduction

Mechanistic support for a causal role of ambient air pollution in the development of asthma and allergic rhinoconjunctivitis is strong.1 Evidence from prospective cohort studies suggests a causal role of ambient air pollution in the development of childhood asthma,1, 2 but is less clear for allergic rhinoconjunctivitis.1

Most published analyses focus on the effect of traffic-related air pollution on asthma and rhinoconjunctivitis throughout early and middle childhood. Findings from the Dutch PIAMA birth cohort study3 showed positive associations between exposure to air pollution in early life and asthma incidence and prevalence during the first 8 years of life. At age 12 years, lifetime risks of asthma remained heightened.4 In the Swedish BAMSE birth cohort,5 exposure to nitrogen oxides (NOx) and particulate matter with a diameter of less than 10 μm (PM10) from traffic during the first year of life was positively associated with prevalent and incident asthma at age 12 years, but not at ages 1, 2, 4, and 8 years. In a cohort of young children from California, new-onset asthma was associated with increasing traffic-related pollution at homes and schools.6 Exposure at birth to particulate matter with a diameter of less than 2·5 μm (PM2·5) was associated with an increased risk of asthma at age 7 years in a cohort from Canada.7 However, no association was shown between nitrogen dioxide (NO2) or particulate matter exposure and asthma prevalence until age 10–11 years in the German GINIplus and LISAplus cohorts8 and one British birth cohort.9 Air pollution tended to be positively associated with hay fever until age 12 years in the PIAMA cohort,4 but associations with rhinitis prevalence were heterogeneous across study regions of the GINIplus and LISAplus cohorts.8

Heterogeneity between findings might be partly explained by differences in exposure assessment, definition of health outcomes, and statistical analysis. Previous multicohort analyses with harmonised exposure and health data have been limited to cross-sectional analyses of asthma prevalence at specific ages.10 Moreover, statistical power to assess age-specific associations with air pollutions in individual cohorts, in particular for onset of disease, is often limited by small numbers. Therefore, we used the framework of the European collaborative Mechanisms of the Development of ALLergy (MeDALL) project11 to harmonise data for four European birth cohort studies for which a standardised assessment of air pollution exposure is available. We linked estimated residential air pollution exposures to repeated questionnaire reports of asthma and rhinoconjunctivitis throughout childhood and adolescence to elucidate associations between air pollution and onset and presence of disease at different ages.

Research in context

Evidence before this study

No systematic review was done as part of the planning for this study. Evidence from prospective cohort studies suggests a causal role of ambient air pollution in the development of childhood asthma, but is less clear for the development of allergic rhinoconjunctivitis. Studies done so far differ with regard to exposure assessment, health outcome definition, and statistical analysis, which might explain part of the heterogeneity in study findings. In the past few years, cohort-specific cross-sectional analyses with subsequent meta-analyses of the association between air pollution and asthma prevalence, but not incidence, at specific ages were undertaken in five European cohorts with harmonised exposure and health data. Age-specific associations with air pollution have been studied in single cohorts, but statistical power is low, particularly for onset of disease.

Added value of this study

For the first time, we were able to pool data from four large prospective birth cohort studies. We included data from repeated follow-up assessments up to age 14–16 years and made full use of these data by undertaking longitudinal rather than cross-sectional analyses. We studied associations with incidence in addition to prevalence and estimated both overall and age-specific effects.

Implications of all the available evidence

We recorded adverse effects of exposure to air pollution early in life on asthma incidence and prevalence, in particular after the age of 4 years when asthma can be more reliably diagnosed. Our results strengthen the evidence for the contribution of ambient air pollution to the development of asthma in children and adolescents, and suggest that reductions in levels of air pollution could help to prevent the development of asthma in children.

Section snippets

Study design and participants

In this population-based birth cohort study, we pooled data of participants from four European birth cohort studies designed to investigate the development of asthma and allergies in Stockholm county, Sweden (BAMSE12); two parts of Germany (the Munich metropolitan area and the northwestern part of North Rhine-Westphalia (Wesel area), referred to as South and North, respectively (GINIplus13 and LISAplus14); and a series of communities in the north, west, and centre of the Netherlands (PIAMA15).

Results

Our study sample included 98% of the original participants from the BAMSE (4010/4089 [98%]) and PIAMA (3867/3962 [98%]) cohorts and roughly 80% of the original participants from the GINI and LISA North (2691/3390 [79%]) and South (3558/4416 [81%]) cohorts. The table shows characteristics of the study population and figure 1 shows frequency distributions of health outcomes. More than a third of the participants from the BAMSE and PIAMA cohorts, and 10–15% of those from the GINI and LISA cohorts,

Discussion

Our findings provide evidence for positive associations of exposure to NO2 and PM2·5 absorbance early in life with incidence and prevalence of asthma, but not rhinoconjunctivitis, throughout childhood and adolescence. The adverse effects of air pollution on asthma incidence and prevalence were more consistent after age 4 years than before that age.

The present study, using data from four large prospective birth cohort studies with 14–16 years of follow-up, is a major extension of previous

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