Prenatal exposure to polycyclic aromatic hydrocarbons, or PAH, a component of air pollution, raises the odds of behavior problems associated with attention deficit hyperactivity disorder, or ADHD, at age 9, according to researchers at the Columbia Center for Children's Environmental Health at the Mailman School of Public Health. Results are 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, and 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 symptoms that characterize ADHD—specifically inattentive-type ADHD at age 9—compared with children whose mothers did not have high PAH exposure. 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," says lead author Frederica Perera, DrPH, PhD, director of the Center and professor of Environmental Health Sciences at the Mailman School. "The findings are concerning because attention problems are known to impact school performance, social relationships, and occupational performance."
The Centers for Disease Control 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 using PAH-DNA adducts in maternal blood obtained at delivery. Childhood PAH exposure was measured by PAH metabolites in urine at ages 3 or 5 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 3, reduced IQ at age 5, and symptoms of anxiety/depression and attention problems at ages 6 and 7.
The mechanism by which PAH exposure increases the likelihood of ADHD is not fully understood, but the paper lists several possibilities, including the disruption of the endocrine system, DNA damage, oxidative stress, and interference 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. Moreover, ADHD imposes large annual costs to society, estimated between $36 and $52 billion in the U.S. and to individuals, estimated to be $12,005 to $17,458.
The study was supported by the National Institute for Environmental Health Sciences (NIEHS) and the U.S. Environmental Protection Agency (US EPA) (grants NIEHS/EPA P01ES09600/R82702701, NIEHS/EPA P01ES09600/RD832141, NIEHS/EPA P01ES09600/RD834509, NIEHS R01ES08977), the John & Wendy Neu Family Foundation, the New York Community Trust, and the Blanchette Hooker Rockefeller Fund.
Additional co-authors include Hsin-wen Chang, Deliang Tang, Emily L. Roen, Julie Herbstman, Amy Margolis, Tzu-Jung Huang, Rachel L. Miller, Shuang Wang, and Virginia Rauh—all with the Columbia Center for Children's Environmental Health at the Mailman School.
About Columbia University's Mailman School of Public Health
Founded in 1922, Columbia University's Mailman School of Public Health pursues an agenda of research, education, and service to address the critical and complex public health issues affecting New Yorkers, the nation and the world. The Mailman School is the third largest recipient of NIH grants among schools of public health. Its over 450 multi-disciplinary faculty members work in more than 100 countries around the world, addressing such issues as preventing infectious and chronic diseases, environmental health, maternal and child health, health policy, climate change & health, and public health preparedness. It is a leader in public health education with over 1,300 graduate students from more than 40 nations pursuing a variety of master's and doctoral degree programs. The Mailman School is also home to numerous world-renowned research centers including ICAP (formerly the International Center for AIDS Care and Treatment Programs) and the Center for Infection and Immunity. For more information, please visit http://www.mailman.columbia.edu.