The Pollution-IQ Equation Smog Is Affecting More than Asthma Rates—It's a Factor in Falling IQ Scores

Smog is more than just a health hazard for the elderly and asthmatic. The latest research suggests living near a busy roadway with higher-than-average smog may be linked to lower IQ scores and other health impacts in developing newborns.

Smog occurs when ground-level pollution mixes with pollutants like those released from car and truck tailpipes and from coal-burning power plants’ smokestacks, creating a dense haze. A 2007 study from the Harvard School of Public Health found the first link between smog and falling IQ scores in children. Researchers conducted two intelligence tests—the Kaufman Brief Intelligence Test and the Wide Range Assessment of Memory and Learning—at ages 8 and 11 for 202 Boston-area children. After controlling for other factors, the numbers showed children living and attending school in areas with higher levels of traffic pollutants scored an average of 3.7 points lower than children living in less polluted areas.

Lead researcher Shakir Franco Suglia reported that smog particles could be reaching, and impacting, the brain. It’s well established that exposure to lead and high levels of fluoride can inhibit intelligence. But a number of studies published in 2009 suggest that the problem starts before birth. Evidence suggests a correlation not only between smog and IQ, but also between smog and other health problems affecting the growing infant pre- and post-birth, including preclampsia, low birth weight, small head circumference and miscarriage.

In the April 9, 2009, edition of the Journal of Epidemiology and Community Health, a study linked high concentrations of traffic pollution with slow fetal development. In particular, the study noted, exposure to fine particle matter in the first and third trimesters, and nitrogen dioxide throughout pregnancy. Led by professor David Rich, the research team from the University of Medicine and Dentistry in New Jersey collected data from 336,000 birth records from babies born over a span of five years. They then compared that information to levels of smog recorded by the Environmental Protection Agency’s pollution monitoring sites in the area.

Controlling for other risk factors such as smoking and drug use, a link was discovered between women living in areas with high traffic pollutants and smaller-than-average babies. When published, Rich and his team stressed that just living near a well-traveled roadway might be enough to affect fetal growth.

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In January 2010, a study was published in the Environmental Health Journal with similar findings. In that trial, a Spanish research team followed 785 women and their newborns in and around Valencia. They collected samples looking for levels of nitrogen dioxide near the women’s homes, and conducted interviews with participants to help rule out other risk factors. Again scientists found that women living in areas with high levels of smog gave birth to smaller babies with smaller head sizes.

Some researchers believe that traffic pollution acts like secondhand smoke or marijuana use, restricting oxygen and nutrients delivered to the fetus. Others, like Dr. Shuk-mei Ho, chair of the Environmental Health Department at the University of Cincinnati in Ohio, believe prenatal exposure to pollutants changes human cell development and causes problems later in life.

Published in 2009 in PLoS ONE, a study by researchers from the University of Cincinnati and Columbia University in New York delved into the specific reasons that inner city kids were prone to higher asthma rates. Along with looking at pollutant exposure after birth, researchers monitored pregnant mothers and analyzed umbilical cord blood. Their results showed that mothers exposed to higher levels of traffic-related polycyclic aromatic hydrocarbons—or PAHs—gave birth to infants whose blood contained a DNA sequence associated with asthma. And recent studies in the U.S. and Brazil attribute high-pollution conditions to higher rates of miscarriage.

We often think of smog as an environmental ill—a side effect of higher temperatures brought on by global warming. New evidence shows that efforts to reduce smog may in fact accelerate global warming, because when you reduce nitrogen oxides in the air it has the unfortunate side effect of increasing the amount of methane—and methane is a potent global warming gas. Simultaneously reducing methane—a byproduct of coal mines and animal farms—is one way to reduce that eventuality. But beyond smog’s environmental problems are its very real and immediate public health ones.

Not only does traffic pollution make it harder for people to breathe on days when the smog alerts are high, it impacts the health and development of children exposed pre- and post-birth, and can lead to serious, lifelong problems.

HILARY EVANS is a freelance journalist living in North Central Iowa.