By Kathleen Doheny
WEDNESDAY, March 25, 2015 (HealthDay News) -- Exposure to common air pollutants before birth may make children more likely to have the symptoms of attention-deficit/hyperactivity disorder (ADHD) and other thinking and behavioral problems, a small new study suggests.
"Exposure to air pollution in pregnancy and during early infancy [and] early childhood seems to produce brain disturbances in the left side of the brain, in direct proportion to the amount of exposure to air pollution that women experience in pregnancy," explained study author Dr. Bradley Peterson. He directs the Institute for the Developing Mind at The Saban Research Institute of Children's Hospital Los Angeles.
Peterson's team has been following 620 minority women who live in New York City. The researchers are planning to eventually scan 250 children born to the women, gathering information about the mothers' exposure to air pollutants during pregnancy and after.
For the new study, Peterson said, "we selected out 40 who had minimal exposure to other substances we know produce brain problems," so the team could focus on the effects of pollutants called PAHs.
PAH stands for polycyclic aromatic hydrocarbons. They are common in the environment, coming from motor vehicle emissions, oil and coal burning for power or home heating, agricultural burning, wildfires, hazardous waste sites, charred food and tobacco smoke.
The children in the study have been followed from before birth through ages 7 to 9. The children and their mothers enrolled during the years 1998 through 2006.
The researchers used MRIs to measure the children's brains and tested the children to see if they had symptoms related to ADHD or other problems. They found that prenatal exposure to the pollutants was linked with thinking and behavioral problems. The greater the exposure, the worse the brain changes and the more likely the kids were to have ADHD symptoms or other issues.
In earlier research, the team had found that exposure to PAHs during gestation was linked with several problems, including developmental delays by age 3, reduced verbal IQ at age 5 and anxiety and depression by age 7.
In the new study, the researchers found reductions in the white matter surface of the brain's left hemisphere. This type of reduction is linked to slower processing of information during IQ tests and more severe problems in behavior, including ADHD symptoms and aggression, the researchers said. Being exposed after birth was linked to additional white matter changes linked to problems in concentration and problem-solving ability.
The findings were published online March 25 in the journal JAMA Psychiatry.
Peterson couldn't explain for sure why the higher exposure was linked with more brain problems, although he noted that animal studies have found exposure to PAHs kills nerve cells in the brain. However, not all animal research translates into humans and the study only found an association between air pollution exposure and developmental problems in childhood, not a cause-and-effect link.
The research is ongoing, Peterson said. Even though the number of children studied was small, the ''purity'' of the number studied can somewhat make up for that limitation, he added.
Another expert said the finding should be taken seriously.
"I think the study provides some evidence for an anatomical basis for ADHD,'' said Dr. Enme Corrales Reyes, a pediatric neurologist at Nicklaus Children's Hospital, formerly Miami Children's Hospital. The findings should ideally spur government and other public health officials to control exposure to the PAHs, Reyes added.
Peterson said that while women may not have the option of moving away from a polluted area to help protect their unborn children, they can take steps to minimize exposure.
Those who smoke should stop, and those who don't should avoid secondhand smoke, he said.
When outside, they should avoid pollutants as much as possible. For example, if a truck is emitting a blast of diesel exhaust, avoid it if you can, he said.