A child who lives near a freeway has double the risk of autism compared to other kids, researchers from California revealed in the journal Environmental Health Perspectives. There has been a considerable increase in autism diagnoses over the last few years, which cannot be fully explained just by more awareness and changes in diagnostic criteria, the authors explained. According to the CDC (Centers for Disease Control and Prevention), the incidence of autism in the USA rose by 57% between 2002 and 2006.

The researchers are from Children’s Hospital Los Angeles, the Keck School of Medicine of the University of Southern California (USC) and the UC Davis MIND Institute.

Study author, Heather Volk, PhD, MPH, said:

    “Children born to mothers living within 309 meters of a freeway appeared to be twice as likely to have autism.”

The authors believe that genetics together with environmental factors may play a significant role in the increase in autism rates.

Previous studies had shown that exposure to air pollution during pregnancy can have a negative impact on a fetus’ development. Some articles in academic journals had also identified a possible link between air pollution during an infant’s first years of life and cognitive developmental delay. This is the first study, the authors wrote, to identify a link between autism risk and vehicular traffic pollutants.

The researchers gathered data from the Childhood Autism Risks from Genetics and Environment (CHARGE) study. They compared children with autism and typically developing kids. They were aged between 24 and 60 months when the study began and lived in Los Angeles, Sacramento and San Francisco. Controls were recruited from the state of California birth files and were matched for frequency to the autism cases by gender, age, and broad geographic area. Each family was evaluated with a personal visit. All the children were assessed, and autism assessment was carried out using well-validated instruments.

The investigators tracked where the mothers lived while pregnant, during their first, second and third trimesters, as well as when the babies were born. They also noted what distance each household was from a freeway or major road. Gestational ages of participants were identified with the help of ultrasound measurements as well as prenatal records.

They found that a baby at birth whose household was within 309 meters (1013.7 feet) of a freeway had double the risk of having autism compared to other babies. Even after making adjustments for the baby’s sex, educational levels of household members, the mother’s age, prenatal smoking and ethnicity, the link remained the same.

The link was only there when close to a freeway, not a major road, the authors wrote.

Human and toxicological studies have shown that traffic-related air pollutants trigger inflammation and oxidative stress. The authors note that the growing evidence that inflammation and oxidative stress play a role in the development of autism supports the findings of their study.

Irva Hertz-Picciotto, PhD, principal researcher on the CHARGE study, said:

    “We expect to find many, perhaps dozens, of environmental factors over the next few years, with each of them probably contributing to a fraction of autism cases. It is highly likely that most of them operate in conjunction with other exposures and/or with genes.”

“Residential Proximity to Freeways and Autism in the CHARGE study”
Heather E. Volk, Irva Hertz-Picciotto, Lora Delwiche, Fred Lurmann, Rob McConnell
Environ Health Perspect :-. doi:10.1289/ehp.1002835

Written by Christian Nordqvist