Babies who are exposed to lots of traffic-related air pollution in the womb and during their first year of life are more likely to become autistic, according to a U.S. study.
The findings, which appeared in the Archives of General
Psychiatry, support previous research linking how close children
live to freeways to their risk of autism, the study's lead
author says.
"We're not saying traffic pollution causes autism, but it
may be a risk factor for it," said Heather Volk, an assistant
professor at the Keck School of Medicine of the University of
Southern California in Los Angeles.
The prevalence of autism has grown over the past few years,
and it's now estimated that the disorder - which runs a spectrum
from a profound inability to communicate and mental retardation
to milder symptoms seen in Asperger's Syndrome - affects one in
every 88 children born in the United States.
The increase in autism diagnoses has also been accompanied
by a growing body of research on the disorder. Volk's new study,
however, is one of a series of looks into how environmental
factors may be linked to a child's risk of being autistic, and
done over the past few years.
"I think it's definitely an area that's been understudied
until recently," Volk said.
While Volk and her colleagues used how close a child lived
to a freeway as a substitute for pollution exposure in their
last study, this time they looked at measures of air quality
around the children's homes.
Compared to 245 California children who were not autistic,
the researchers found that 279 autistic children were almost
twice as likely to have been exposed to the highest levels of
pollution while in the womb, and about three times as likely to
have been exposed to that level during their first year of life.
The found that children exposed to the highest amount of
"particulate matter" - a mixture of acids, metals, soil and dust
- had about a two-fold increase in autism risk.
Volk and her colleagues also saw a similar link between
autism and nitrogen dioxide, which is in car, truck and other
vehicle emissions.
"This is a risk factor that we can modify and potentially
reduce the risk for autism," wrote Geraldine Dawson, of the
University of North Carolina at Chapel Hill, in an email to
Reuters Health. Dawson wrote an editorial that accompanied the
study.
The researchers said certain pollutants could play a role in
brain development, but that doesn't prove that being exposed to
air pollution makes children autistic. They warned that there
may be other factors that explain the association, including
indoor pollution and second-hand smoke exposure.
"There are some potential pathways that we're examining in
our current research that will be coming up next," Volk said.