A new study linking the likelihood of autism and ADHD symptoms in early life to in-utero exposure to a common plasticizer is no doubt going to cause a stir.
It’s another chapter in the ongoing search for answers to some pretty complex questions, like why autism and ADHD diagnoses are on the rise, and why so many children around the world seem to be afflicted with behavior problems, and what the chemicals in plastics could be doing to our brains.
And while it’s an interesting addition to the research, there are very specific things this new study can (and can’t) tell us about all these hot topics in science, and what patterns are emerging between them.
Let’s get into it.
The study, published in Med (a peer-reviewed journal owned by Cell Press), looked at children’s behavioral traits at ages two and four, and how they correlate with the child’s potential prenatal exposure to the common plastic additive DEHP.
DEHP (di-(2-ethylhexyl) phthalate) is a synthetic chemical that helps make plastics more flexible. It’s often used in vinyl furniture upholstery, garden hoses, shower curtains, medical tubing, and vegan leathers.
It’s also known to easily leach out of the material it was added to, which is how it can end up in our food, water, and ultimately, our bodies.
“Chemical exposure levels are mainly determined at the population level and are not easily a matter of personal choice,” explains Anne-Louise Ponsonby, neuroepidemiologist at the University of Melbourne in Australia.
“Plastic chemicals like DEHP are often ingested, so government safety regulations around food processing and packaging are very important.
“Global plastic control efforts should take into consideration recent evidence as it emerges on the need for health protection, particularly for vulnerable populations such as pregnant women and young babies.”
Animal experiment studies and observational studies in humans have picked up links (that’s correlation, not cause) between DEHP exposure in utero and neurodevelopment issues, including symptoms generally associated with ADHD and autism.
The new study probes further into this association, and especially the epigenetic factors that some suspect could be involved in a causal link, if there is one.
Epigenetics is a scientific discipline that examines the way environmental factors – like exposure to DEHP – affect the way genes function, even though the DNA sequences in the organism are unchanged.
DNA methylation is one way an epigenetic effect can occur, in which methyl (CH3) groups latch on to genes and either increase or decrease their expression.
“What we have found is a possible biological explanation and one that provides new evidence that exposure to DEHP in pregnancy may contribute to autism and ADHD,” says the study’s lead author Sam Tanner, bioinformatics analyst at the University of Melbourne.
“Our study found infants exposed to higher levels of DEHP before birth showed distinctive changes in DNA methylation – an epigenetic switch that turns genes on or off – in their umbilical cord blood at birth.
“Children who carried this ‘epigenetic signature’ went on to show more autism- and ADHD-related symptoms at ages two and four, with clearer effects in males than females.”
This observational study draws on data from 847 Australian mothers and their babies, who participated in the Barwon Infant Study, with 589 of the mother-infant pairs providing a complete set of data points.
The researchers started collecting data before the children were even born. At 36 weeks into their pregnancy, each mother provided a single urine sample.
In these samples, the researchers looked for metabolites that would help them estimate how much DEHP a mother was probably taking into her body on a daily basis. These metabolites are pretty reliable indicators of DEHP exposure: they are the byproducts our bodies produce when breaking down this specific phthalate.
And then, when the babies were born, DNA was extracted from their umbilical cord blood and analyzed for epigenetic signatures that might be linked to DEHP exposure.
A group of 531 genes, affected by methylation patterns that seemed to occur together, appeared to mediate 21 percent of the link between estimated DEHP exposure and the autism and ADHD symptoms that were measured when the children reached ages 2 and 4.
Another test for methylation, based on 1,000 sites across the genome, pointed to the same conclusion, giving some extra weight to the possibility that DEHP could be contributing to the symptoms.
Importantly, these links were only really significant among boys.
We should be wary of several aspects of this method.
For one, a single urine sample may not necessarily be representative of what’s normal for a person over the long run.
Also, the developing baby’s potential DEHP exposure here is based on an estimate, which was based on a proxy measurement (urine), not a direct measurement (actual DEHP levels in the fetus, placenta, or uterus, for instance).
And, as medical researcher Mirko Uljarevic reiterates, this study is observational, not experimental, so it cannot prove cause and effect.
“Autism and ADHD are complex conditions; however, the measures used by the authors were not developed for the purpose of comprehensively assessing autism or ADHD; rather, they provide very limited information,” says Uljarevic, who was not involved in the research.
What he means here is that the behavioral symptoms being measured in the study – which were based on questionnaires filled out by the children’s parents – are not actually clinical diagnoses of ADHD or autism.
They highlight behaviors that might warrant further investigation for a diagnosis when the child reaches school age, but they’re not conclusive (and are also fairly subjective).
“Crucially, the authors could not test the full chain from chemical exposure to brain changes to symptoms, only part of it,” Uljarevic adds.
Together, the findings present some interesting patterns, but it remains impossible to say DEHP has any specific health effect based on these results.
Related: A Low-Plastic Diet Has Detectable Impacts on Urine Levels Within a Week, New Experiment Shows
“The current study offers important avenues for future research; however, autism, ADHD, and other neurodevelopmental conditions are multifactorial conditions that arise from many genetic and environmental factors together,” Uljarevic concludes.
“No single exposure like this is likely, on its own, to meaningfully change an individual child’s risk.”
The research was published in Med.
This article was fact-checked by Michael Irving and edited by Michael Irving. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
