For decades, scientists have known that air pollution harms people's bodies. Microscopic particles released by the burning of coal, oil and gasoline slip into people’s lungs and bloodstreams and trigger asthma and heart attacks.
Now it looks like air pollution might impair our minds, too.
A new study published in the Journal of the American Medical Association Psychiatry suggests that smoke-like emissions from vehicles and industry reduce the development of white matter in the brains of children. With less of this important wiring in the brain, children – especially in urban areas, with more air pollution – process information more slowly, and tend to be more hyperactive and aggressive.
These are the conclusions of Dr. Bradley Peterson, Director of the Institute for the Developing Mind at Children’s Hospital in Los Angeles, and colleagues working at Columbia University. They published a study on air pollutants called Polycyclic Aromatic Hydrocarbons, which are released by the incomplete burning of coal, diesel, wood, and other fuels.
"We found that exposure to higher levels of certain air pollutants during pregnancy and infancy seems to produce a distinct pattern of abnormality in growth and development of brain tissue, especially in white matter of the left side of the brain, the left hemisphere," Dr. Peterson said. “And these abnormalities were huge.
They extended form the front of the brain to the back of the brain, and the magnitude of the abnormalities was in direct proportion to the level of exposure to air pollutants in fetal life. So air pollution exposure in fetal life seems to produce long lasting disturbances to the growth and development of brain tissue.” How did the researchers figure this out? They had 665 pregnant mothers in New York City wear back-pack like air monitors that measured their exposure to Polycyclic Aromatic Hydrocarbons (also called PAH’s). Because tobacco is also a source of these pollutants, the scientists excluded smokers and people who lived in homes with anyone who smoked.
After their children were born, the researchers picked the 40 most representative kids and studied their air and health for a decade. They gave the kids intelligence tests, monitored their behavior and attention spans. And scientists had the children submit to brain scans with magnetic resonance imaging (MRI) machines to measure the development of white matter in their brains.
The researchers found a clear correlation between pollution levels, brain development, and behavior, Dr. Peterson said. "The logical consequence and conclusion is that the more air pollution exposure we have the more it will produce this form of brain disturbance and the more it will produce ADHD-like behaviors in children," Dr. Peterson said. "And that could lead to some of the increasing prevalence of ADHD and other behavioral problems that we see in our nation’s children."
Dr. Paul Strickland, a professor at the Johns Hopkins Bloomberg School of Public Health, said the new study is the most recent of a series of papers that have made an important contribution to the understanding of the impact of air pollution on brains.
But I asked him: Could the rise in children diagnosed with ADHD (Attention Deficit Hyperactivity Disorder) really be caused by pollution? That’s a tricky subject, in part because more doctors diagnosing the disorder does not necessarily mean there is more of the disorder. Dr. Strickland had another concern about the theory. “I think that’s unlikely,” he said of the rise in ADHD being drivenby a rise in air pollution. “And the reason is that over the last several decades – maybe 30 or 40 years – we’ve actually had a decline in particulate pollution in this country, due to regulation of industry and particularly automobile exhaust.
We are much better, for example, in Baltimore today that we were, say, 20 years ago, in terms of PAH (polycyclic aromatic hydrocarbon air pollution).” Dr. Strickland did note that, even though air pollution – both particulates and polycyclic aromatic hydrocarbons, which are closely related – is down overall, this pollution is still generally higher in urban areas than rural communities.
So air pollution could be contributing to an array of stresses – including poverty and poor nutrition -- that make it harder for kids in urban areas and elsewhere to perform in school and in life. The research is not conclusive yet. But it is possible that reducing the burning of fossil fuels could not only help the climate, but also make us smarter.
