Prenatal Exposure to Air Pollution Harms Baby's Brain

Megan Brooks

March 31, 2015

A neuroimaging study provides more evidence that prenatal exposure to common air pollutants (polycyclic aromatic hydrocarbons [PAH]) may contribute to cognitive and behavioral impairment in children.

Dr Bradley Peterson

"The clinical and public health implications of these findings are enormous, particularly given the ubiquity of PAH in the environment and the large number of people who are exposed to high levels of PAH," Bradley S. Peterson, MD, director, Institute of the Developing Mind, Children's Hospital Los Angeles, in California, told Medscape Medical News.

These exposures are "likely" leading to increased rates of attention-deficit/hyperactivity disorder (ADHD) and externalizing problems in children, he said.

"Our findings in this new brain imaging study gives us important information about how specifically PAH are affecting brain structure and how those alterations in brain structure in turn lead to the PAH-related cognitive and behavioral problems seen in our cohort and other cohorts around the world," Dr Peterson added.

The study was published online March 25 in JAMA Psychiatry.

Major Implications

Emissions from motor vehicles, the burning of oil and coal for home heating or power generation, wildfires, agricultural burning, hazardous waste sites, tobacco smoke, and charred foods are all sources of exposure to PAH, which readily cross the placenta and affect the developing brain, the researchers note.

An earlier study of more than 600 mother-baby pairs recruited from minority communities in New York City showed that exposure to airborne PAH during gestation was associated with multiple cognitive and emotional disturbances in childhood, including development delay by age 3 years, reduced verbal IQ at age 5, and symptoms of anxiety and depression at age 7.

The current study included 40 minority urban school-aged children born to Hispanic (Dominican) or African American women. They were followed from before birth to ages 7 to 9 years.

Brain MRI showed that prenatal PAH exposure led to reductions in "nearly the entire white matter surface of the brain's left hemisphere ― losses that were associated with slower processing of information during intelligence testing and more severe behavioral problems, including ADHD and aggression," said Dr Peterson.

Furthermore, "postnatal PAH exposure ― measured at age 5 ― was found to contribute to additional disturbances in development of white matter in the dorsal prefrontal region of the brain, a brain region that supports concentration, reasoning, judgment, and problem-solving ability," he said.

The authors note that the study was limited to a minority population with a high level of poverty and low educational attainment and therefore may not be generalizable to other populations, although impoverished urban minority populations are disproportionately exposed to air pollutants. The sample size was also limited. The researchers are now conducting a much larger study to confirm and extend their findings.

Dr Peterson believes that health providers "should educate prospective parents, especially early in pregnancy, about these risks and urge them to avoid, to the extent possible and for the health of their baby, exposure to smoke, exhaust, and other sources of PAH."

"Policies that reduce the level of environmental PAH exposure and the prevalence of these PAH-related brain abnormalities can have tremendous societal impact not only by reducing the personal suffering that these problems cause in children and families but also by reducing the economic consequences of these adverse long-term outcomes," he concludes.

Biological Mechanism

Commenting on the findings for Medscape Medical News, Marie Pedersen, PhD, of the Danish Cancer Society Research Center, Copenhagen, Denmark, who was not involved in the research, described the study as "very interesting."

"It is new to use MR imaging in environmental epidemiological studies, and there are very few studies assessing the association between air pollution and cognitive functions in children using MR imaging," she explained. "The study population is selected due to higher risk and higher exposures than the general US population, so I am not surprised of the reported findings. The findings are in line with previous reports by the authors of effect of PAH exposure...on neurodevelopment," Dr Pedersen noted.

Marc Weisskopf, PhD, ScD, of the Departments of Environmental Health and Epidemiology, Harvard T. H. Chan School of Public Health, in Boston, Massachusetts, believes the study adds "important underlying biological underpinnings of potential air pollutant effects. It always helps to add biological mechanisms to the epidemiological literature on the main exposure and behavioral outcome," said Dr Weisskopf, who was not involved in the research.

The study was funded by the National Institute of Environmental Health Sciences, the US Environmental Protection Agency, and the National Institute of Mental Health. The authors have disclosed no relevant financial relationships.

JAMA Psychiatry. Published online March 25, 2015. Abstract

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