In utero exposure to the chemical phthalate has been linked with autistic traits in young boys in an analysis published Wednesday in the journal Environmental Health Perspectives.
The authors also noted that folic acid -- taken in the form of a dietary supplement -- may block the effects of phthalate, a group of endocrine-disrupting chemicals present in cosmetics and other common household products, and other toxic chemicals in the womb. Phthalates are also used in certain plastics, food packaging, and medical devices.
The study is the first to find this particular protective effect.
"One of the most important findings is how adequate folic acid supplementation in pregnancy may offset the potential harmful effects of phthalates in regard to autistic traits," co-author Youssef Oulhote, assistant professor of biostatistics and epidemiology at UMass-Amherst, said in a press release.
While autism spectrum disorder, or ASD, "undoubtedly" has an underlying genetic basis, Oulhote and his colleagues noted, the study's findings add to evidence that prenatal exposure to toxic chemicals contributes to the development of certain social impairment traits. Boys are four times more likely to develop ASD than girls.
The researchers analyzed data from the Maternal-Infant Research on Environmental Chemicals, or MIREC, project, which enrolled 2,001 women during their first trimester of pregnancy from 10 cities in Canada between 2008 and 2011.
To date, researchers have produced more than 70 papers in peer-reviewed scientific journals based on MIREC data.
For the new study, the team measured 11 different phthalate metabolites in the pregnant women's urine samples taken during their first trimester and recorded the women's folic acid supplement intake. Later, they performed neuropsychological assessments on 601 three- and four-year-old children of the participating women, screening for ASD.
In general, they found that increases in urinary concentrations of phthalate chemicals were associated with increases in the presence of ASD traits. Fewer of these autistic traits -- which are characterized by social behavior, repetitive behaviors, and restricted interests, but do not necessarily constitute an autism diagnosis -- were found among boys whose mothers had taken the recommended dose of supplementary folic acid -- 400 mcg daily -- during their first trimester of pregnancy.
The links between phthalate exposure and ASD traits were more significant in boys than in girls, the authors said.
"We do not know if these subtle effects associated with prenatal phthalate exposure will last after the preschool period," said child development specialist and study co-author Gina Muckle, professor at Université Laval and Quebec-CHU Research Center in Quebec City, Canada.
The authors added that most of the women in the study were white, employed, married or living with a partner, and well-educated. Cosmetics and other personal care products free of phthalates tend to be more expensive.
"These are not the higher exposures for certain phthalates you will find in low-income communities," Oulhote said.