"However, whether or not the potential association between autism and traffic-related air pollution exists, reduction of traffic-related air pollution would be good for public health."

Car Emissions May Hike Autism Risk

By Cole Petrochko, Staff Writer, MedPage Today
Published: November 26, 2012
Reviewed by Zalman S. Agus, MD; Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania



Car Emissions May Hike Autism Risk

Car Emissions May Hike Autism Risk

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This study was designed to examine the relationship between traffic-related air pollution using measures of nitrogen dioxide and particulate matter and autism.

The investigators found that children with autism were more likely to live at residences that had the highest exposure to traffic-related air pollution, during gestation and during the first year of life.


Early life and prenatal exposure to nitrogen dioxide and air pollutants generated by traffic was associated with autism, researchers found.

Children with autism were more likely to live in homes in the highest quartile of exposure to traffic-related air pollution during gestation (adjusted odds ratio 1.98, 95% CI 1.20 to 3.31) and during the first year of life (aOR 3.10, 95% CI 1.76 to 5.57), compared with control children, reported Heather Volk, PhD, MPH, of the University of Southern California in Los Angeles, and colleagues.

Regional exposure measures of nitrogen dioxide and particulate matter less than 2.5 μm and 10 μm in diameter were also associated with autism during gestation, they wrote online in the Archives of General Psychiatry.

The authors noted that the associations were strongest "during late gestation and early life, although it was not possible to adequately distinguish a period critical to exposure," and that infants with autism "were three times as likely to have been exposed during the first year of life to higher modeled traffic-related air pollution."

However, they cautioned that further study of likely biological pathways was necessary to determine causality.

They analyzed relationships between traffic-related air pollution, air quality, and autism through a case-control study of 279 children with autism and a 245-child control group with typical development.

Participants were 24 to 60 months old at baseline, were born in California, and were enrolled in the CHARGE study (Childhood Autism Risks from Genetics and the Environment). They were also "frequently matched" by sex, age, and geographic region.

The study sample was mostly male (84%) and white (50%), and there was no difference between cases and controls in demographic, socioeconomic, or lifestyle variables.

To measure for air quality and pollutants, mothers' addresses from birth certificates and residential history questionnaires were used to estimate trimester-based and first year pollution exposures, which were based on regional data from the Environmental Protection Agency's Air Quality System.

The authors included exposures to nitrogen dioxide, ozone, and particulate matter measuring less than 2.5 μm and 10 μm in aerodynamic diameter when measuring associations between autism and environment. They also noted that prior research had found associations between parental and early-life exposure to high levels of air pollutants with poor birth outcomes, immunologic changes, and decreased cognitive abilities.

Among pollutants, only particulate matter and nitrogen dioxide exposure were significantly tied to risk of autism, while there was no association seen between autism risk and ozone exposure.

Nitrogen dioxide exposure during the child's first year was associated with a greater risk of autism (aOR 2.06, 95% CI 1.37 to 3.09), and was associated with an increased risk throughout pregnancy (aOR 1.81, 95% CI 1.23 to 2.65).

The risk also was higher during the second (aOR 1.62, 95% CI 1.17 to 2.25) and third (aOR 1.64, 95% CI 1.18 to 2.29) trimesters. First trimester exposure was associated with a nearly 50% increased risk of autism (aOR 1.47, 95% CI 1.05 to 2.20).

Particulate matter less than 2.5 μm was associated with greater than two-fold risks of autism during the child's first year (aOR 2.12, 95% CI 1.45 to 3.10) and throughout pregnancy (aOR 2.08, 95% CI 1.93 to 2.25). The second (aOR 1.48, 95% CI 1.40 to 1.57) and third trimesters (aOR 1.40, 95% CI 1.11 to 1.77) were significantly associated with risk of autism. However, there was no association between third trimester exposure and autism.

Particulate matter less than 10 μm had a significant association with risk of autism during the first year (aOR 2.14, 95% CI 1.46 to 3.12), throughout pregnancy (aOR 2.17, 95% CI 1.49 to 3.16), and during the first (aOR 1.44, 95% CI 1.07 to 1.96), second (aOR 1.83, 95% CI 1.35 to 2.47), and third trimesters (aOR 1.61, 95% CI 1.20 to 2.14).

Volk and co-authors noted that variation between local and regional levels of air pollution could inform follow-up studies to "understand both individual pollutant contributions and the effects of pollutant mixtures on disease," as well as establishing the biological pathways involved in the association between pollution and autism.

The authors noted that their study may be limited by unmeasured confounders, lack of measurement of trimester-specific effects, and lack of generalizability of the study population.

In an accompanying editorial, Geraldine Dawson, PhD, of the University of North Carolina at Chapel Hill, pointed out that in recent years, the "upsurge of [autism] research parallels a dramatic increase in autism prevalence," adding that in the last 6 years, the prevalence of autism spectrum disorder has increased 78% and the estimated annual cost of autism has more than tripled.

The findings from Volk's study highlight "the need for more research on prenatal and early postnatal brain development in autism, with a focus on how genes and environmental risk factors combine to increase risk for autism spectrum disorders," she said.



The study was funded by grants from the National Institute of Environmental Health Sciences.

Volk reported receiving speaker support from Autism Speaks.

Two co-authors are employees of Sonoma Technology.

Another co-author received support from a legal settlement between the South Coast Air Quality Management District and British Petroleum.


Primary source: Archives of General Psychiatry
Source reference:
Volk HE, et al "Traffic-related air pollution, particulate matter, and autism" Arch Gen Psychiatry 2012; DOI: 10.1001/jamapsychiatry.2013.266.

Additional source: Archives of General Psychiatry
Source reference:
Dawson G, et al "Dramatic increase in autism prevalence parallels explosion of research into its biology and causes" Arch Gen Psychiatry 2012.




Autism: Traffic pollution linked, study suggests

Heavy traffic in

San Diego, California


26 November 2012 Last updated at 22:14 ET Share this pageEmailPrint
Autism: Traffic pollution linked, study suggests
By James Gallagher
Health and science reporter, BBC News

The possibility that autism is linked to traffic pollution has been raised by researchers in California.

Their study of more than 500 children said those exposed to high levels of pollution were three times more likely to have autism than children who grew up with cleaner air.

However, other researchers said traffic was a "very unlikely" and unconvincing explanation for autism.

The findings were presented in the Archives of General Psychiatry journal.

Data from the US Environmental Protection Agency were used to work out levels of pollution for addresses in California.

This was used to compare exposure to pollution, in the womb and during the first year of life, in 279 children with autism and 245 without.

The researchers from the University of Southern California said children in homes exposed to the most pollution "were three times as likely to have autism compared with children residing in homes with the lowest levels of exposure".

They have previously shown a link between autism and living close to major roads.

They warn that there could be "large" implications because air pollution is "common and may have lasting neurological effects".

But how?
However, other researchers questioned how pollution could alter the brain's development and lead to autism.

Uta Frith, a professor of cognitive development at University College London, said: "It seems to me very unlikely that the association is causal."

She said the study did not "get us any further since it does not present a convincing mechanism by which pollutants could affect the developing brain to result in autism".

One of the challenges with this style of study is that it is difficult to account for every aspect of life which might affect the probability of developing autism, such as family history.

It means the study cannot say that autism is caused by traffic pollution, merely that there could be a link between the two.

Sophia Xiang Sun, from the University of Cambridge's autism research centre, argued that cutting pollution would be a good idea anyway.

"We know that traffic-related air pollution can contribute to many other diseases and conditions, and it is biologically plausible it also has a role in pathways of autism.

"However, whether or not the potential association between autism and traffic-related air pollution exists, reduction of traffic-related air pollution would be good for public health."

More on This Story

What is autism?

Autism and Asperger's syndrome are part of a range of disorders that can cause difficulties with communication and social skills
The conditions can lead to isolation and emotional problems for those living with them
Conditions can vary from very mild, where the person can function as well as anyone else, to so severe they cannot take part in normal society
The conditions are collectively known as autistic spectrum disorders and affect more than 580,000 people in the UK
Source: BBC Health