Air pollution may raise autism risk
27th November 2012 - Being exposed to high levels of air pollution from traffic may raise the risk of autism, according to researchers.
" Children exposed to higher levels of traffic-related pollutants during pregnancy or during the first year of life were at increased risk of autism compared to children exposed to the lowest level," says Dr Heather Volk, assistant professor of research at the University of Southern California Keck School of Medicine.
The risk differed depending on timing.
During pregnancy, the highest exposures to pollution doubled the risk of autism, she says. High levels during the child's first year tripled the risk.
The study is published online in the Archives of General Psychiatry.
Air pollution & autism risk
Autism is a diverse disorder marked by problems in communicating and interacting socially. There are over half a million people with autism in the UK. That’s one person in every 100.
Researchers have been looking at the potential role of air pollution in autism for only about three years, says Dr Volk.
Air pollution has been linked with a variety of ill health outcomes, she says, including babies being born small for their gestational age. "When you think about the birth outcome literature, looking at air pollution [and autism risk] makes some sense."
In 2011, Dr Volk's team reported a higher risk of autism for children whose families lived within about 300 metres (1,000 feet) of a motorway.
For the new study, she looked at data from 279 children with autism and a comparison group of 245 children without it.
At the time they started, the children were aged two to five years.
Dr Volk used the mothers' addresses to estimate exposure to pollution during each trimester of pregnancy and during the child's first year of life.
Researchers used information from the Environmental Protection Agency and did traffic modelling to work out how much traffic-related air pollution there was at each location. They also looked at exposure to particulate matter and nitrogen dioxide.
In her previous study, Dr Volk says, she just looked at how far people lived from roads. The new study went further:"Now we consider how busy the road was, traffic density, volume of traffic, and how often the road is travelled."
The risk of autism was higher for those exposed to more pollution, either before birth or during their first year.
Based on the findings, however, Dr Volk says she can't say that living in a specific area is worse than another.
For instance, those who live in a rural area might be close to a very busy high-traffic intersection, increasing pollution exposure.
She found a link or association. It does not prove cause and effect.
The link held after she considered other factors that affect risk, such as prenatal smoking, the mother's age, race and ethnicity.