The environment has long been suspected as a possible cause of autism. Now a new study from the University of Southern California shows that mothers exposed to high levels of air pollution during pregnancy and during the first year of their baby’s life are three times as likely to have an autistic child.
“Exposures to traffic-related air pollution, particulate matter and nitrogen dioxide were associated with an increased risk of autism,” the authors wrote in the Archives of General Psychiatry.
Researchers looked at over 500 children who were enrolled in the Childhood Autism Risks from Genetics and the Environment study in California. About half of the children were diagnosed with autism.
Researchers used mothers’ addresses to estimate their exposure to traffic-related air pollution, based on air quality data from the Environmental Protection Agency. They found that air pollution had a quantitative, measurable impact on a child’ susceptibility to developing autism.
Children living in homes with the highest levels of traffic-related air pollution were three times as likely to have autism compared with children living in homes with the lowest exposure. Exposure to high levels of particulate matter and nitrogen dioxide were highly correlated to autism, while there was little association with ozone pollution.
“Although additional research to replicate these findings is needed, the public health implications of these findings are large because air pollution exposure is common and may have lasting neurological effects,” wrote lead author Heather E. Volk, PhD, of the University of Southern California.
An earlier study by Volk and her colleagues found that living near a freeway was associated with autism, but that study only relied on distance from a freeway as a proxy for air pollution. The new study builds on that earlier research.
“The results provide more convincing evidence that exposure to local air pollution from traffic may increase the risk of autism. Demographic or socioeconomic factors did not explain these associations,” Volk said.
Autism is a diverse disorder with genetic and environmental factors likely contributing to its origins. It is characterized by problems in communication, social interaction and repetitive behaviors. The incidence rate of all autism disorders is now reported to be as high as 1 in 110 children.
Previous studies have found that polycyclic aromatic hydrocarbons reduce the expression of a gene that is important in early neurodevelopment and is markedly reduced in autistic brains. Researchers have also found that that traffic-related air pollution induces inflammation and oxidative stress in the brain, which may be associated with autism.
Volk says that even though the emerging evidence suggests that environment plays a role in autism, there is only limited information available about what exposures are relevant, their mechanisms of action, the stages in development in which they act and the development of effective of preventive measures. She called for further research into the epidemiological and toxicological associations with autism.
In an accompanying editorial also published in the Archives of General Psychiatry, Geraldine Dawson, Phd, of the University of North Carolina at Chapel Hill, wrote, “In the past six years alone, the prevalence of autism spectral disorder (ASD) has increased 78 percent and the estimated annual cost of autism has more than tripled.”
“Despite a substantial increase in autism research publications and funding during the past decade, we have not yet fully described the causes of ASD or developed effective medical treatments for it. More research is needed to develop strategies for preventing or reducing the disabling symptoms associated with this highly prevalent and costly neurodevelopmental disorder,“ she concluded.