Early prenatal exposure to phthalates — the synthetic chemicals commonly found in household items and personal care products — has been tied to language delays in children, new research shows.

In the first study of its kind, the collaboration between investigators from the Icahn School of Medicine at Mount Sinai, New York City, and Karlstad University, Sweden, showed that the risk for language delay was as much as 30% greater in children whose mothers were exposed to twice the levels of dibutyl phthalate and butyl benzyl phthalate, two chemicals commonly found in such everyday items as cosmetics, plastic toys, and food.

"The bottom line here is that the phthalates that a mother is exposed to in early pregnancy can affect the development of the brain in her children, particularly in this area of language development," principal investigator Shanna Swan, PhD, professor of environmental and public health at the Icahn School of Medicine at Mount Sinai, told Medscape Medical News.

"Unfortunately, these results point to different phthalates than we've found to be bad actors in the past. We've previously observed negative associations with di-ethylhexyl phthalate, which is more commonly found in food. Now we have more phthalates to worry about," said Swan.

The study was published online October 29 in JAMA Pediatrics.

Onus on Regulators, Manufacturers

Phthalates — high-volume semivolatile synthetic chemicals that make plastic soft and flexible — are used in a variety of industrial products, including polyvinyl chloride flooring, food packaging, personal-care products, medical supplies, and even toys. Their chemical structure precludes them from leaching, which is why they are often found in indoor air, dust, food, and water.

Global biomonitoring data show that most phthalate metabolites are ubiquitous in the urine of children and adults alike. It is also present in blood, breast milk, and amniotic fluid.

Previous research in both animals and humans has demonstrated that phthalates are endocrine disruptors with antiandrogenic properties. Indeed, prenatal phthalate exposure has been associated with male genital defects. Moreover, studies found inverse associations between phthalate metabolite level in prenatal urine and subsequent child neurodevelopment, behavioral outcomes, mental and psychomotor development, and neurologic status.

Given that language-development delays can affect academic achievement later in life, such delays serve as an important indicator of later neurodevelopmental impairment.

With that in mind, the investigators sought to examine the association between metabolite phthalate level in first-trimester urine samples and subsequent language development in early childhood.

The researchers used data from two independent pregnancy cohort studies for the analysis — the Swedish Environmental Longitudinal, Mother and Child, Asthma and Allergy study (SELMA; 963 pregnant women and their children) and the Infant Development and Environment Study (TIDES; 370 women and their children). The latter study was conducted in the United States.

In both trials, phthalate levels were obtained from the women at their first prenatal visit (median, 10th week of pregnancy). After their children were born and had begun acquiring language, the women were asked how many words their children understood (at 30 months in SELMA and 37 months in TIDES) through use of a screening questionnaire. The questionnaire is routinely used in Sweden and was translated into English. Responses were categorized as <25, 25 to 50, and >50 words. Children who understood <50 words were classified as having language delay.

Both studies found that 10% of children used 50 words or fewer; 2.7% understood fewer than 25 words. Interestingly, language delay was more common among boys than girls in both studies.

Raw analyses of the data demonstrated that metabolites of two chemicals — dibutyl phthalate and butyl benzyl phthalate — were statistically significantly associated with language delay.

After adjusting for potential confounders, a doubling of prenatal exposure to these two metabolites increased the odds ratio of language delay by 25% to 40%. These adjusted findings were significant in the Swedish study but not in the American study. The researchers attribute this difference to the smaller sample size in the US study.

The investigators note that the current study is one of the first to examine the association between early language development and first-trimester phthalate exposure. The findings have far-reaching implications, given the ubiquity of phthalates in modern society.

"Until there's some testing of chemicals before they're put into products, we're not going to get around this," Swan said. "I don't think consumers can do very much, because these things aren't labeled. You don't know what's in your furniture, and you certainly don't know which foods have phthalates in them.

"So the consumer is at a loss," Swan added. "It really is the responsibility of the regulators and the manufacturers."

Exposure Difficult to Avoid

Commenting on the findings for Medscape Medical News, Susan Schantz, PhD, professor of toxicology and neuroscience at the University of Illinois in Urbana, who was not involved in the study, said the findings are very much needed.

"We did a review a couple of years back looking at environmental chemicals and language development, and I was shocked to see how little research there was on this really important aspect of neurodevelopment," said Schantz.

"Phthalates are present in many different consumer products," Schantz added. "So it's very hard to avoid exposure. I think studies like this are important because we need to start phasing phthalates out of products and find better, less toxic solutions."

"I don't know what the answer is," Swan concluded, "but I know we'd be doing pregnant women and their children a service if we could keep some of these chemicals out of their bodies."

The studies were supported by grants from the National Institute of Environmental Health Sciences, the Swedish Research Council Formas, and the County Council of Varmland, Sweden.

JAMA Pediatrics. Published online October 29, 2018. Abstract