Pregnant women exposed to high levels of air pollution are twice as likely to have a child with autism compared to women exposed to low levels, scientists from Harvard School of Public Health (HSPH) reported in Environmental Health Perspectives (June 18th edition).
The authors claim that theirs is the first large nationwide study to examine associations between air pollution and ASD (autism spectrum disorder) rates across the United States.
Lead author Andrea Roberts, a research associate in the HSPH Department of Social and Behavioral Sciences, said:
“Our findings raise concerns since, depending on the pollutant, 20% to 60% of the women in our study lived in areas where risk of autism was elevated.”
Previous studies have shown how methylene chloride, lead, mercury, manganese, diesel and other particulates found in polluted air can affect the physical and neurologic development of the fetus and baby. Two studies have already demonstrated a link between air pollution exposure during pregnancy and ASD risk. However, they only examined three locations in the country.
Roberts and colleagues gathered and examined data from the Nurses’ Health Study II, which began in 1989 and included details on 116,430 nurses. They focused on data on 325 women who gave birth to a child who was eventually diagnosed with an autism spectrum disorder and 22,000 others whose children did not have the disorder.
The team analyzed environmental data from the EPA (US Environmental Protection Agency) to estimate how much air pollution the mothers were exposed to while pregnant. They also factored in some possible confounders, such as smoking during pregnancy, education and income. The main aim was to look at links between autism spectrum disorders and pollution levels at the time and place of birth.
The authors found that the pregnant mothers living in the 20% of areas with the most air pollution had twice the risk of having a child with autism, compared to those living in the 20% of locations with the lowest levels. The researchers focused on levels of diesel particulates and/or mercury in the air.
Regarding other pollutants, such as lead, methylene chloride, manganese, and combined metal exposure, a 50% higher risk of autism in offspring was found among those who had been living in areas with the highest levels during their pregnancy, compared to those with the least exposure.
There was a closer association between autism risk during pregnancy and pollution levels if the mother was carrying a boy, the researchers added. However, whether girls are less affected by air pollution should be examined further because there were many more boys with autism in the study than girls, i.e. there were not enough girls with an ASD in the study.
Senior author Marc Weisskopf, said:
“Our results suggest that new studies should begin the process of measuring metals and other pollutants in the blood of pregnant women or newborn children to provide stronger evidence that specific pollutants increase risk of autism. A better understanding of this can help to develop interventions to reduce pregnant women’s exposure to these pollutants.”
Researchers form USC (University of Southern California) and the Children’s Hospital of Los Angeles published a report in Archives of General Psychiatry which showed that exposure to air pollution during a child’s first 12 months of life may increase autism risk.
In another study, published in Environmental Health Perspectives, scientists found that children living near a freeway had twice the risk of autism compared to other kids.
ASD (autism spectrum disorder) and autism both refer to a group of complex brain development disorders. A person with an ASD typically has difficulties in social interaction, verbal communication, non-verbal communication, and repetitive behaviors.
Examples of ASDs include:
- Asperger’s syndrome
- Autistic disorder
- Childhood disintegrative disorder
- Pervasive developmental disorder not-otherwise-specified (PDD-NOS)
- Rett Syndrome
According to specialists, autism has its roots in the very early stages of brain development. Symptoms of ASD usually emerge when the child is two to three years of age.
According to the CDC (Centers for Disease Control and Prevention), approximately 1 in every 88 children in the USA has an ASD – ten times as many as four decades ago. ASDs are much more common in boys than girls; 1 in every 54 boys and 1 in every 252 girls have been diagnosed with an ASD in America.
It is estimated that about two million Americans live with an ASD.
Written by Christian Nordqvist