Over the last decade, the number of children in the U.S. who suffer from autism has skyrocketed. In 2002, the Centers for Disease Control and Prevention estimated that one out of every 150 children would be affected by the genetic condition. By 2012, the CDC revised that number to one out of every 50 children. While better understanding and ways of testing for the condition account for part of that increase, researchers still remain baffled by what remains the primary cause for the rise in children born with autism.
Now a recent study has found evidence that might explain another possible factor behind this three-fold rise of autism cases. According to researchers at the Harvard School of Public Health, pregnant women who live in areas with heavy smog may have twice the risk of having a child with autism.
While researchers were quick to point out that the study did not find a clear cause and effect relationship between smog and autism, it did find a strong association that suggests pollution could contribute to autism rates.
The results of the study were published online in Environmental Health Perspectives.
The Dangers of Dirty Air
To collect their data, researchers compared the amount of air pollution 325 women who had given birth to a child with autism were exposed to in relation to 22,000 women who had given birth to a child without autism. The mothers who participated in the study were enrolled in the Nurses’ Health Study II, an ongoing program that has followed the health of approximately 117,000 women since 1989.
As part of the study, researchers measured each woman’s exposure to certain pollutants, such as methylene chloride, mercury, manganese, lead, diesel particulate matter, and overall metal exposure.
Of the women involved, between 20 to 60 percent lived in areas considered as highly polluted at any one time. Those who lived in the areas with the highest levels of mercury or diesel particulates in the air had twice the risk of giving birth to a child with autism when compared to women who lived in areas with the lowest levels of these two pollutants.
Additionally, women who lived in areas that had the highest levels of methylene chloride, manganese, lead, and combined metal exposure were 50 percent more likely to give birth to a child with autism when compared to women who lived in areas with the lowest concentration of these pollutants.
These findings remained consistent even after researchers took into account other known risk factors for autism, such as education, income, and whether the mother smoked during her pregnancy. Overall, participants who lived in either condition were more likely to give birth to a boy with autism than a girl.
The results of this study only add more compelling data to the notion that the air a woman breathes while pregnant can strongly influence the development of her child. Studies have previously shown women who live near a freeway have a higher risk of giving birth to a child with autism, but those were conducted on a local level, while this latest research used data from women living across the country.
While researchers don’t know why breathing in pollutants seems to have an effect on the developing minds of infants, they do consul that by definition, pollution has a negative effect on the body. And even though pollution may only play a small role in the increase in the number of children born with autism, the results of this study provide further evidence that a child’s development is influenced by both genetics and nature.