Hyperactivity in children linked to plastic additive, BPA.

Children in the U.S. with higher levels of BPA in their bodies were more likely to have Attention-Deficit/Hyperactivity Disorder (ADHD), according to a study.

The study of 460 children across the U.S. aged 8 to 15 years old found that 11 percent of those with BPA levels higher than the median level had ADHD. In contrast, 3 percent of those children with BPA levels below the median had ADHD.

The research, published online last week in the Environment Research journal, adds to evidence that children’s BPA exposure may alter brain development and lead to behavior problems such as reduced attention and hyperactivity. ADHD is the most common behavior disorder in U.S. children, causing them to have trouble concentrating and controlling their behavior.

It’s unclear what causes the disorder, but research suggests a mix of genetics and exposure to some environmental chemicals, such as BPA, which is known to disrupt hormones critical for developing brains.

The association was stronger for boys than girls, which reflects broader ADHD rates. Nationally about 10 percent of children between 5 and 17 have had an ADHD diagnoses, with boys having a much higher rate at 14 percent. By comparision about 6 percent have the disorder, according to the U.S. Centers for Disease Control and Prevention.

“You’d expect to see differences between the two sexes,” said Laura Vandenberg, an assistant professor of environmental health at the University of Massachusetts Amherst, who was not involved in the study. BPA mimics estrogen hormones.The sexes use hormones differently to influence brain function.

Overall boys seem to have a higher risk for neurological problems, and “we’re not entirely sure why that is, said Sarah Evans, an instructor at the Icahn School of Medicine at Mount Sinai, who was not involved in the current study. “It’s possible the male brain is maybe more vulnerable to environmental exposures.”

BPA—used to make plastic hard and shatterproof and to extend the shelf life of canned food—can leach out of can linings and into the food. Studies show that just about everyone has traces of the chemical in their body—for instance, 97 percent of the children in this study had BPA in their urine.

The additive has been linked to multiple health impacts in exposed babies and children—including obesity, asthma, low birth weights and genital defects.

A 2014 study on prenatal exposure to BPA found higher levels meant more behavior problems for school-age boys. Evans, lead author of that study, said prenatal exposure to chemicals is a “window of high susceptibility,” but so are the childhood years. The brain keeps developing into the 20s.

Research specifically looking at ADHD and BPA exposure has been mixed, with some finding a link and some not. Most of the previous studies, however, have been on children younger than 8 years old, and ADHD and its symptoms are often realized later than that.

“It’s hard to get an idea whether preschoolers have ADHD or not, as it’s normal for preschoolers to have behaviors that in an older child would be considered ADHD,” said Dr. Tanya Froehlich, senior author of the new study and a developmental-behavioral pediatrician at the Cincinnati Children's Hospital Medical Center.

Animal studies show that BPA may alter the body’s dopamine—a chemical messenger that helps people think and stay alert and focused. “Dopamine systems are modulated by estrogen and BPA is a synthetic estrogen,” Froehlich said.

There are also suggestions that BPA can interact with thyroid hormones—“critical in normal brain development,” Evans said.

The study was limited in that the researchers used a single urine test to determine exposure, as BPA is quickly eliminated from the body, and they don’t know what the children’s prenatal or early childhood exposure to the chemical was. “We’d really like to see levels of BPA exposure over time and how they correlate with risk to ADHD, we had this single snapshot with their levels at the time of the study,” Froelich said.

It’s also possible that kids with ADHD happen to have different eating habits and children with hyperactive behavior are eating poor foods with more BPA contamination, Vandenberg said.