The odds of having a child with autism were more than double (2.46 times higher) for families living less than 309 meters (approx 1000 ft) from a "freeway." Doctors at the Children’s Hospital Los Angeles, University of Southern California determined family proximity to high traffic roadways for 304 children with autism and 259 non-autistic children. Using specific addresses of each family, the 485 total children were divided into groups of 10% (called deciles) depending on the distance of their residence to a 4 lane freeway. Read more below.
The most striking difference came when comparing families living the closest 10% to the freeway (less than 300 meters) to the 10% of families living the farthest away (more than 5,150 meters). Those living in the closest group had a 2.48 times greater risk of having a child with autism. A unique design of this study is scientists chose to use 10% quintiles of exposure for comparison rather than the 25% quartiles typically used in other studies. This allows for observing a more accurate consequence of exposure. Being that autism is now affecting close to 1 in 30 children today (2024), a doubling of autism rates (as seen here) would result in 1 in 15 being diagnosed with autism. This study, by extension, also raises serious concerns of higher rates of autism for pregnant mothers spending extended time driving in busy roadway traffic as well.
The scientists concluded by stating,
"Our analysis is the first step in examining a hypothesized relationship between air pollutants and autism. It has been estimated that 11% of the U.S. population lives within 100 m of a four-lane highway, so a causal link to autism or other neurodevelopmental disorders would have broad public health implications.
ABSTRACT
Background: Little is known about environmental causes and contributing factors for autism. Basic science and epidemiologic research suggest that oxidative stress and inflammation may play a role in disease development. Traffic-related air pollution, a common exposure with established effects on these pathways, contains substances found to have adverse prenatal effects.
Objectives: We examined the association between autism and proximity of residence to freeways and major roadways during pregnancy and near the time of delivery, as a surrogate for air pollution exposure.
Methods: Data were from 304 autism cases and 259 typically developing controls enrolled in the Childhood Autism Risks from Genetics and the Environment (CHARGE) study. The mother's address recorded on the birth certificate and trimester-specific addresses derived from a residential history obtained by questionnaire were geocoded, and measures of distance to freeways and major roads were calculated using ArcGIS software. Logistic regression models compared residential proximity to freeways and major roads for autism cases and typically developing controls.
Results: Adjusting for sociodemographic factors and maternal smoking, maternal residence at the time of delivery was more likely be near a freeway (≤ 309 m) for cases than for controls [odds ratio (OR)=1.86; 95% confidence interval (CI), 1.04-3.45]. Autism was also associated with residential proximity to a freeway during the third trimester (OR=2.22; CI, 1.16-4.42). After adjustment for socioeconomic and sociodemographic characteristics, these associations were unchanged. Living near other major roads at birth was not associated with autism.
Conclusions: Living near a freeway was associated with autism. Examination of associations with measured air pollutants is needed.