Nov. 20 (UPI) -- Children prenatally exposed to air pollution have a high risk of developing autism spectrum disorder, a new study says.
The study, published in the Monday edition of JAMA, examined more than 130,000 kids born in Vancouver between 2004 and 2009.
"We analyzed air pollution data in Vancouver over the same period to assess air pollution exposures in the pregnant woman," Lief Pagalan, lead author of the study and a member of the faculty of health sciences at Simon Fraser University, told CNN. "Their children were followed up for at least 5 years to see if they were diagnosed with autism spectrum disorder."
Researchers contrasted autism rates for children born to women who the least air pollution exposure to the children born to women with the most.
In all, they diagnosed about 1 percent of the kids with autism by age five.
The three air pollution measurements -- particulate matter, nitrogen dioxide and nitric oxide -- all link to autism development.
Children prenatally exposed to higher levels of PM2.5, or particulate matter under 2.5 micrometers in diameter, had a 1.04 percent risk of developing autism. Those odd rise to 1.06 percent with exposure to higher levels of nitrogen dioxide and 1.07 percent with exposure to higher levels of nitric oxide.
Another study found that mothers who lived close to highways in Los Angeles had a higher risk of giving birth to children who developed autism.
The cause of autism still remains a mystery.
One researcher said the study doesn't include enough factors in its attempt to pinpoint the cause of autism.
Robin P. Goin-Kochel, associate director for research at Texas Children's Autism Center, said the study excluded the socioeconomic status of the mother as another important factor determining the cause of autism.
"Also, the focus was on the mothers' residential locale, and it's possible that mothers' work locales have a different environmental makeup that might be important to consider," Goin-Kochel told CNN. "It's possible that these pollutants and/or other exposures have an influence on fathers and the quality of their sperm."
Many experts think the air pollution has a minimal effect on whether a child develops autism. One researcher pointed to another potential cause that the study neglected to consider.
"Autism is strongly genetic. We know this because it runs in families," said James Cusack, director of science at U.K.-based Autistica, to the Science Media Centre. "Other differences which were not measured, such as genetic differences, may explain this increase. This study does not provide evidence that air pollution causes autism."
However, the study's lead author thinks his work has helped to narrow down the list for potential causes.
"Identifying environmental risk factors helps identify opportunities for prevention," Pagalan said to CNN.