Several previous studies indicate that living near major roadways increases risk of asthma, but the association between risk of asthma and the exposure to on-road commuting exposure to air pollution has not been explored.
We used time and distance from school to home as an indicator of commuting exposure in a cohort of 4737 kindergarten and first grade children participating in the southern California Children’s Health Study. Time and distance from school to home was obtained by using a PERL program employing the routines of MAPQUEST. We examined the relationships between prevalent asthma, lifetime asthma, late onset asthma [diagnosed age 5 or later], early [before age 4] and late onset wheeze [age 4 or later], and commuting time at the time of study entry in 2003.
Compared with children in the lower quartile of commuting time, those in the upper quartile were more likely to have lifetime asthma (OR 1.31; 95%CI 1.01–1.71), prevalent asthma (OR 1.29; 95%CI 0.98–1.70), late onset asthma (OR 1.94; 95%CI 1.01–3.74), and late onset wheeze (OR 1.44; 95%CI 1.00–2.10), but not early onset wheeze or asthma. These associations were robust to confounding by socio-demographic and household characteristics and by traffic-related exposure modeled at the home of the child (which was independently associated with asthma). Similar associations were obtained between asthma and commuting distance to school.
These results suggest that commuting may increase the risk of asthma. However, the latency from entry to school was short, range of commuting time was modest (upper quartile range from 5 to 44 minutes) and exposure would have been misclassified by this crude index. (Information about actual commuting route, other on-road travel, and traffic volume was not available). Therefore, it is possible that (1) these results could be explained by other unmeasured confounders, (2) school commuting time may have been a proxy for on-road travel elsewhere, or (3) effects of even modest on-road exposure were substantial.