Residential proximity to main roads during pregnancy and the risk of allergic disorders in Japanese infants: The Osaka Maternal and Child Health Study

The role of traffic-related air pollution in the initiation of allergic disorders in children is still not clearly understood. The present prospective study examined the relation between proximity of the home during pregnancy to the nearest main road, which was used as a surrogate for traffic-related air pollutants, and the risk of allergic disorders in Japanese infants in an urban area. Subjects were 756 mother-child pairs. Distance of each subject's home during pregnancy from the center line of all of the 235 main roads in Osaka Prefecture was computed using geographical information system software. The first survey during pregnancy and the second survey between 2 and 9 months post-partum collected information on potential confounding factors. In the third survey, which was from 16 to 24 months post-partum, a self-administered questionnaire included questions on allergic disorders. In the third survey, 22.1% and 18.7% of infants became positive for wheeze and atopic eczema based on criteria of the International Study of Asthma and Allergies in Childhood (ISAAC), respectively. The risk of doctor-diagnosed asthma and doctor-diagnosed atopic eczema was 4.4% and 8.9%, respectively. A shorter distance of the residence during pregnancy from the nearest main road was associated with an increased risk of doctor-diagnosed asthma and atopic eczema (adjusted odds ratios for comparison of < 50 m with 200 m or more = 4.01 and 2.26, 95% confidence intervals: 1.44-11.24 and 1.08-4.59, p for trend = 0.02 and 0.03, respectively). No evident relationships were observed between the distance of the residence during pregnancy from the nearest main road and the risk of wheeze or atopic eczema based on the ISAAC criteria. It was difficult to distinguish the effect of the pre-natal from the post-natal exposure because most subjects lived at the same home address both before and after childbirth. Our results are likely to support the hypothesis that intrauterine exposure to traffic-related air pollutants and/or such exposure after birth may increase the risk of more extreme manifestations of allergic disorders in infants.