Having a mother who lived within 1,000 feet of a freeway while pregnant doubles a child's odds of having autism.
The finding comes from a study looking at environmental factors that might play a role in autism. University of Southern California researcher Heather E. Volk, PhD, MPH, and colleagues collected data from 304 California children with confirmed autism and from 259 children who developed normally.
"It has been estimated that 11% of the U.S. population lives within 100 meters [328 feet] of a four-lane highway, so a causal link to autism or other neurodevelopmental disorders would have broad public health implications," the researchers note.
Exposure to air pollution during pregnancy is suspected of a wide range of negative effects on the fetus. A particularly crucial period may be the third trimester, when the brain develops rapidly.
Air pollution is particularly heavy within a thousand feet of a highway. Volk and colleagues found that the 10% of women who lived closest to a freeway during pregnancy were within about 1,000 feet of center line. Children born to these women were 86% more likely to have autism than kids born to women who lived farther from the freeway.
The relationship was stronger for women who lived within 1,000 feet of a freeway during their third trimester. Children born to these women were 2.2 times more likely to have autism.
Interestingly, the odds of autism remained unchanged when the researchers controlled for factors such as child gender or ethnicity, household education, maternal age, and maternal smoking.
It's becoming clear that a child's genetic inheritance has a lot to do with whether that child has autism. But genes do not explain why one child develops autism while another does not. Many researchers believe that something or a combination of things in the environment trigger autism in genetically susceptible kids. That exposure may come while the child is still in the womb.
But what is it about living near a freeway that might trigger autism? Is it really air pollution? Or could it be the noise?
Volk and colleagues note that their findings should be confirmed in studies that measure the actual air pollutants to which pregnant women living near freeways are exposed.
The Volk study appears in the Dec. 16 online issue of Environmental Health Perspectives, published by the U.S. National Institute of Environmental Health Sciences.