The research, conducted in both the United States and Sweden, looked at the levels of phthalates in pregnant women in relation to language development in their children.
Phthalates are a group of chemicals that are present in hundreds of products including toys, vinyl flooring and wall covering, nail polish and perfumes according to the US Food and Drug Administration
. Their uses include making plastics harder to break and more flexible and as solvents, according to the US Centers for Disease Control and Prevention
"When you compare the risk of language delay in mothers with high exposure versus low exposure, it was double the risk. They were twice as likely to have language delay," said Shanna Swan
, one of the authors of the new study. Swan is a professor in the Department of Environmental Medicine and Public Health
at Mount Sinai Icahn School of Medicine.
The study included 963 children and mothers from Sweden, who participated in the Swedish Environmental Longitudinal Mother and Child, Asthma and Allergy Study (SELMA) and 370 mothers and children from the United States, who participated in the Infant Development and the Environment Study (TIDES).
Researchers took urine samples from the mothers early on in their pregnancies, which were measured for the presence of phthalates. A questionnaire was filled out by parents about their child's language development at 30 months old in Sweden and when they were at least 2 years old in the US.
Vocabulary responses were split into groups according to the study: fewer than 25, 25 to 50, and more than 50 words. Any child who had a vocabulary of less than 50 words was considered to have a language delay.
The study found that 10% of both populations (96 of the SELMA children and 37 of the TIDES children) had language delays of vocabularies under 50 words. Twenty-six of the children in Sweden and 10 of the children in the United States used 25 words or less.
Two phthalates appeared to be particularly associated with language delays, according to the study.
"There are two bad actors in this study," Swan said, "dibutyl phthalate and butyl benzyl phthalate." Dibutyl phthalates are found in some personal care products, Swan said. The CDC says that butyl benzyl phthalates are used in products such as vinyl tiles.
"We noticed in both populations, and this is not a new finding, that language delay was more common in boys than in girls, and that's well known," Swan said.
Researchers controlled for factors such as the age of the child, the age of the mother and the educational level of the mother. There was less statistical significance in the results of the US cohort, but the results from both populations "were very consistent. They supported each other," Swan said.
Swan believes the research has a unique selling point. "It's very unusual to have two populations on other sides of the pond, if you will, and very similar response to shared chemicals. These chemicals are in Europe and the United States and they seem to be affecting the children similarly. So, there's a generalizability here that's important," she said. Joseph Braun
, associate professor of epidemiology at the Brown School of Public Health
"What they did here that was unique, was take the data from the two cohorts and analyze it and publish them together and actually show that there was some consistency of the associations and that actually makes it powerful," he said. "We see the same association in two arguably very different places."
The study is not without limitations however, according to Braun, who was not involved with the study.
Because of the nature of phthalates, which Braun says pass through the body very quickly, using only one urine sample from the expectant mothers could mean that the phthalate exposure measured is not typical. "It's a limitation, but not a fatal flaw to the study," he said.
The study adds to a "body of literature suggesting that there's some impact of prenatal phthalate exposure on children's brain development," according to Braun.
For pregnant women or anyone trying to avoid exposure to phthalates, he suggests buying personal care products that are labeled phthalate-free, eating a healthy, balanced diet and trying to avoid food that has been overly processed and packaged. He also suggests having a good dust control regimen, as phthalates present in the home, such as those on vinyl shower curtains, can end up in household dust.
The CDC previously found that exposure to phthalates
was widespread in the United States. The American Academy of Pediatrics
has spoken out about reducing children's exposure to phthalates and other food additives. Earlier this year, the organization released recommendations to help children avoid over-exposure to the chemicals, which it said could "affect male genital development, increase childhood obesity, and contribute to cardiovascular disease."
The group's recommendations included buying and serving more fresh fruit and vegetables and less processed meat, using alternatives to plastic when possible, and avoiding microwaving food or beverages in plastic when possible.
In 2017, the United States Consumer Product Safety Commission
prohibited toys and other children's items that contain certain phthalates.