Air pollution, fetal and infant tobacco smoke exposure, and wheezing in preschool children: a population-based prospective birth cohort

BACKGROUND: Air pollution is associated with asthma exacerbations. We examined the associations of exposure to ambient particulate matter (PM(10)) and nitrogen dioxide (NO(2)) with the risk of wheezing in preschool children, and assessed whether these associations were modified by tobacco smoke exposure. METHODS: This study was embedded in the Generation R Study, a population-based prospective cohort study among 4,634 children. PM(10) and NO(2) levels were estimated for the home addresses using dispersion modeling. Annual parental reports of wheezing until the age of 3 years and fetal and infant tobacco smoke exposure was obtained by questionnaires. RESULTS: Average annual PM(10) or NO(2) exposure levels per year were not associated with wheezing in the same year. Longitudinal analyses revealed non-significant tendencies towards positive associations of PM(10) or NO(2) exposure levels with wheezing during the first 3 years of life (overall odds ratios (95% confidence interval): 1.21 (0.79, 1.87) and 1.06 (0.92, 1.22)) per 10 μg/m(3) increase PM(10) and NO(2), respectively). Stratified analyses showed that the associations were stronger and only significant among children who were exposed to both fetal and infant tobacco smoke (overall odds ratios 4.54 (1.17, 17.65) and 1.85 (1.15, 2.96)) per 10 μg/m(3) increase PM(10) and NO(2), respectively (p-value for interactions <0.05). CONCLUSIONS: Our results suggest that long term exposure to traffic-related air pollutants is associated with increased risks of wheezing in children exposed to tobacco smoke in fetal life and infancy. Smoke exposure in early life might lead to increased vulnerability of the lungs to air pollution.