TUESDAY, June 18 (HealthDay News) -- Pregnant women who live in
smog-filled areas may be twice as likely to have children with
autism, a new study suggests.
"The study does not prove that pollution increases risk for
autism. It found an association," cautioned lead author Andrea
Roberts, a research associate at the Harvard School of Public
Health in Boston. "It adds to the weight of the evidence that there
may be something in air pollution that increases risk for
Researchers compared exposure to air pollution among 325 women
who had a child with autism and 22,000 women who did not. The women
were participants in the Nurses' Health Study II. Pollutants
measured included diesel particulate matter, lead, manganese,
mercury, methylene chloride, and a combined measure of metal
Twenty percent to 60 percent of the women lived in areas
considered highly polluted. And the study showed that: those women
who lived in the 20 percent of locations that had the highest
levels of diesel particulates or mercury in the air were twice as
likely to have a child with autism, compared to those who lived in
the 20 percent of areas with the lowest levels of these
In addition, those who lived in the 20 percent of locations with
the highest levels of lead, manganese, methylene chloride, and
combined metal exposure were about 50 percent more likely to have a
child with autism than those who lived in the 20 percent of areas
with the lowest concentrations.
The findings held even after the researchers took into account
other factors known to affect autism risk, such as income,
education and smoking during pregnancy. Overall, the association
was stronger for boys than it was for girls, but the number of
girls included in the new study was too low to draw any firm
The findings, which were published June 18 online in
Environmental Health Perspectives, do add to a growing body
of research that suggests the air women breathe while pregnant is
one of many factors linked to autism risk. Previous studies have
shown that pregnant women who live in polluted areas or close to
freeways are more likely to have a child with autism, but the
studies were done regionally. The new data is nationwide.
Exactly how, or even if, air pollution affects the developing
brain is murky. "By definition, pollution is stuff that is not good
for us," Roberts said.
Still, the overall increase in autism risk that may be
attributed to pollution is low. "Let's say a woman's risk for
having a child with autism is one in 100, women who live in the
most polluted cities have a risk that is about one in 50, which
means that 49 children would not have autism," Roberts said.
"Even if the risk is doubled, it's still low," she
The U.S. Centers for Disease Control and Prevention now
estimates that about one in 50 children aged 6 to 17 in the United
States has an autism spectrum disorder, the name for a larger group
of disorders that can range from the mild to the severe, and affect
social and communication skills.
Other experts also urged caution in interpreting the new
"There many genes, probably hundreds, and many environmental
factors, probably hundreds, that increase risk of autism," said
Alycia Halladay, senior director for environmental and clinical
sciences at the advocacy group Autism Speaks. "The real message is
that a lot of things cause autism, namely genetics and the
environment and their interaction."
Laura Anthony, the associate director of the Center for Autism
Spectrum Disorders at Children's National Medical Center in
Washington, D.C., said that these risks accrue during pregnancy,
delivery and within the first month of a newborn's life.
"Everything points to that as the critical period. This is the time
when the brain is most sensitive because it is still developing,"
The new findings don't mean that pregnant women should head for
the hills to avoid smog, Anthony added. "Even if you live someplace
rural, you may be exposed to pollution while driving or you could
live in a rural place right next to a plant [or factory]," she
said. "We all need to campaign for cleaner air for a lot of
Dr. Andrew Adesman, chief of developmental and behavioral
pediatrics at Steven and Alexandra Cohen Children's Medical Center
in Lake Success, N.Y., said that the new findings do add weight to
previous studies that looked at the connection between prenatal
exposure to airborn pollutants and later autism.
"While they do validate and affirm what other studies have
found, there are many risk factors and genetic causes identified
with autism," Adesman said. "Even with the strength of this study,
parents can't presume that most cases of autism are due to airborne
contaminants. It's easier said than done to suggest that she move
or not breathe the air."
Learn more about autism at
Department of Health and Human Services.