We have all heard of the warnings of air pollution affecting our health, but a sobering study released last week suggests that even the developing brain of the unborn can be affected. The effect can be so profound, in fact, that it may lead to Attention Deficit Hyperactivity Disorder later on during childhood.
A worrisome new brain imaging study carried out by researchers at the Institute of the Developing Mind, Children’s Hospital in Los Angeles, suggests that prenatal exposure to common air pollutants (polycyclic aromatic hydrocarbons [PAH]), are able to cross the placenta and lead to both developmental and cognitive impairment years later after birth. These pollutants are all around us, and not only include car exhaust, but also emission from burning fossil fuels for energy generation, tobacco smoke and even fumes from charred foods.
The California study included 40 school-aged urban children born to Hispanic or African-American parents, and were followed from before birth to ages 7 to 9 years.
Detailed brain MRIs revealed that prenatal PAH exposure led to distinct changes in the brain, specifically in shrinking of the white matter in the brain’s left hemisphere. This reduction was found to lead to symptoms of ADHD, aggression and other disruptive behaviors, and slower processing speed when performing complex tasks.
“The severity of all these behavioral and cognitive problems are in direct proportion to the magnitude of the PAH-related abnormalities in left hemisphere white matter,” said lead author Bradley Peterson, Director of the Institute for the enveloping Mind, in an interview with Yahoo Canada News.
“These abnormalities are large, extending from the front of the brain to the back of the brain, and their magnitude is in direct proportion to the level of exposure to PAH in fetal life. These findings suggest that pregnant women and young children should avoid, to the extent possible, exposure to smoke, exhaust, and other sources of PAH.”
The brain’s white matter is where fat-coated nerve fibers create web-like communication wiring between different regions of the brain. Disrupting these lines of communication is what Peterson and his team believe produces the ADHD symptoms, behavioral problems, and slow processing of information in children exposed to higher levels of PAH in fetal life and early childhood.
“PAH are likely either damaging those interconnecting fibers or the fatty substance, called myelin, that surround them,” he explained.
This study backs up another recent one by Columbia University, which shows prenatal PAH exposure is associated with developmental delays by the age of three, and anxiety, depression and poor language skills at five years old.
Dr. Stephen Faraone, a leading psychologist and ADHD researcher on the disorder working out of SUNY Upstate Medical University and who is not connected to this study, says that the these new findings are intriguing and that it definitely adds another piece to the ADHD puzzle. However he believes that while the pollution study is first rate, there still isn’t a consensus in the scientific community as to the exact role air pollution may actually play in the manifestation of this disorder.
“While the finding is consistent with the idea that early environmental impacts to the brain may predispose to ADHD, there are not too many studies of air pollution and ADHD, and one [finding] actually disagrees with the idea that early exposure to pollution causes (ADHD),” said Faraone.
The 2014 Swedish study examined over 3,400 twins and tried to correlate symptoms of ADHD with exposure to pre-and post-natal air pollution from local road traffic. Surprisingly no clear correlation was found with neurodevelopment disorders appearing in young children.
More work is clearly needed in this line of research, Faraone says. At the very least, he adds, the new California study is telling us that the entire puzzle is probably a lot more complicated than what many originally thought.
“A key point is that, like genetic risk factors, environmental risk factors, taken alone, have a small effect of ADHD, so parents living in polluted environments should not [automatically] conclude that their children are doomed to develop ADHD,” he added.
There is no doubt the there is an underlying genetic component involved. In recent years, molecular studies of twins show that heritability of ADHD runs at about 75 percent, making it as easy to pass to the next generation as schizophrenia or bipolar disorder.
But with ADHD, what makes it so difficult to pin down the specific genes, is that many are likely involved, and their individual effects would be small and perhaps nearly imperceptible.
Environmental effects contributing to ADHD have been known for many years and are something we can examine in great detail. One source is tobacco smoke, which is one of the more potent sources of PAH in the environment. We have known for decades that smoking during pregnancy increases substantially the risk of babies developing ADHD later on in early childhood. Other known or probable environmental sources include exposures to insecticides, lead, prenatal exposure to alcohol, problems during labor and delivery and head injury.
Unfortunately, exposure to these compounds turns out to be pretty universal for most of the population in North America living in large cities. The fact is that no one can completely escape certain levels of exposure especially in cosmopolitan locales.
Just how serious of a problem could air pollution be in terms of developing ADHD? The latest statistics are worrisome as they indicate that over the past 10 years, rates of ADHD in the United States alone have risen from 7.8 per cent of children in 2003 to 11 per cent in 2011.
No one can escape PAHs in entirety, and many cannot escape high levels of exposure.
But if the effects seen in this small sample of children followed in this new study are extrapolated to the entire population who are being exposed to air pollutants during fetal life or early childhood, the public health implications become staggering, says Peterson.
“Pregnant mothers and young children, should avoid even second-hand exposure to tobacco smoke, and they should, to the extent possible, avoid heavy exposure to burning organic materials, including gas and diesel exhaust from cars, trucks, and buses,” he pointed out.
“This may be the price we pay for living in an industrialized, technological society, but we know with certainty that governmental and environmental regulations can dramatically reduce the levels of air pollution to which we are all exposed.”