Scientists have described for the first time the biochemical mechanism linking attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) to the common but problematic compound bisphenol A (BPA). Building on previous studies of ADHD and BPA exposure, researchers from the Rowan-Vertua College of Osteopathic Medicine and Rutgers New Jersey Medical School found that people with neurodevelopmental disorders have a harder time expelling BPA from their bodies.
"[This is] the first conclusive biochemical evidence of a link between BPA and the development of autism or ADHD," said first author T. Peter Stein, professor of surgery at Rowan-Vietua University. "We were surprised to find that ADHD suffers from the same deficit in BPA detoxification."
In 2016, U.S. researchers found that children with ADHD had significantly higher concentrations of BPA in their urine. This was confirmed two years later by a large Chinese study, which found that schoolchildren with ADHD had significantly higher urinary concentrations of both bisphenol A and 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage.
To date, there are few data on the metabolic processes associated with exposure to BPA and neurodevelopmental diseases in humans.
Bisphenol A, an industrial compound that hardens plastics, has been used in food packaging since the 1960s. It is found in a variety of common products, including polycarbonate beverage bottles, food packaging and containers. Earlier this year, the U.S. Food and Drug Administration backed its previous stance on the chemical's use in consumer products, saying "BPA is safe at current levels in foods."
Bisphenol A is also an endocrine disruptor that interferes with the body's natural hormones, affecting cellular responses and important endocrine pathways. Recent research shows that long-term exposure to BPA can interfere with dopamine transmission, a key area of brain dysregulation in ADHD.
Stein and his team are studying the glucuronidation process in children: 66 children with ASD, 44 children with ADHD, and 37 children without neurodevelopmental problems. Glucuronidation is a key process in the liver that adds sugar molecules to toxins, making them more soluble in water so they can be eliminated from the body more quickly. While this process varies from person to person, the inability to process BPA quickly can expose body tissue to the toxin for longer.
They found that children with ADHD were about 17 percent less able to efficiently glucuronidate added sugar molecules than controls. The glucuronidation process of children with ASD is about 10% worse.
"The clearance of BPA is a 'major pathway' or it would not have been detected so easily in a modest-scale study," Stein said.
ASD and ADHD are complex, multifactorial neurodevelopmental disorders that cannot be attributed to one cause. However, little is known about how the interaction between environmental factors and genes contributes to both diseases.
The team also notes that not every child with ADHD or autism is unable to process BPA correctly, and there are few studies of older children or adults with these neurodevelopmental disorders. BPA has been linked to cognitive impairment, reproductive problems, cancer and type 2 diabetes. Recent research suggests that consumers should not view its "alternative" bisphenol S as a healthier choice.
The research was published in the journal PLoSONE.