A new study suggests exposure to dirty air during pregnancy increases the risk of odds of behavior problems associated with attention-deficit hyperactivity disorder, or ADHD.

Researchers at the Columbia Center for Children’s Environmental Health at the Mailman School of Public Health discovered prenatal exposure to polycyclic aromatic hydrocarbons, or PAH, a component of air pollution, could influence the development of ADHD.

The study is published online in the journal PLOS ONE.

The researchers followed 233 nonsmoking pregnant women and their children in New York City from pregnancy into childhood.

They found that children born to mothers exposed to high levels of PAH during pregnancy had five times the odds of a higher-than-usual number and degree of ADHD symptoms as compared with children whose mothers did not have high PAH exposure.

The symptoms were associated with inattentive ADHD, characterized by difficulty focusing and maintaining attention.

The study is the first to explore the connection between prenatal PAH and ADHD in school-age children over time.

“This study suggests that exposure to PAH encountered in New York City air may play a role in childhood ADHD,” said lead author Frederica Perera, Dr.P.H., Ph.D.

“The findings are concerning because attention problems are known to impact school performance, social relationships, and occupational performance.”

The federal Centers for Disease Control and Prevention estimates that around 10 percent of American children have ADHD in one of three types: inattentive ADHD, in which children have a hard time focusing and are easily distracted and disorganized; hyperactive and impulsive ADHD; or a combination of the two.

Little is known about what causes ADHD, but, in addition to genes, environmental factors are known or suspected to play a role.

PAH are toxic air pollutants generated by many sources, such as traffic, residential boilers, and electricity generating plants using fossil fuel.

Researchers measured levels of maternal PAH exposure in maternal blood obtained at delivery.

Childhood PAH exposure was measured by PAH metabolites in urine at ages three or five years. ADHD behavior problems were assessed using the Conners’ Parent Rating Scale.

The current findings build on the center’s previous studies linking prenatal PAH exposure with behavioral and cognitive issues, including associations with developmental delay at age three, reduced IQ at age five, and symptoms of anxiety/depression and attention problems at ages six and seven.

Although the mechanism by which PAH exposure increases the likelihood of ADHD is not fully understood, researchers list several possibilities.

Investigators believe PAH exposure could disrupt the endocrine system, cause DNA damage, inflict oxidative stress, and interfere with placental growth factors resulting in decreased exchange of oxygen and nutrients.

Although more research is needed to fully understand this relationship, the researchers say these results are of concern since children with ADHD are at greater risk for risk-taking behaviors, poor academic performance, and lower earnings.

Source: Columbia University Mailman School of Public Health/EurekAlert