Pregnant women exposed to higher levels of air pollutants had children with lower IQs, compared to the children of women exposed to lower levels, a new study reports.

Researchers looked at 1,005 pregnant women participating in the Conditions Affecting Neurodevelopment and Learning study, set in Shelby County, Tennessee, and assessed the IQs of their offspring between the ages of 4 and 6.

As reported in Environmental Research, the findings show a negative association between IQ and exposure to PM10—pollutant particles with a diameter of one-seventh the width of a human hair that come from industry, power plants, cars, air traffic, and railways. Children with mothers in the highest 10 percent of exposure had IQ scores 2.5 points lower than those in the lower 10 percent.

When the researchers looked at plasma levels of maternal folate, found naturally in leafy vegetables, beans, and citrus fruit, and recommended for all pregnant women in its synthetic form as folic acid, they found the difference between offspring IQs in the highest and lowest PM10-exposed groups had widened to 6.8 points among those whose mothers had the lowest levels (bottom 25 percent) of folate.

PM10 exposure had no impact on IQ if maternal levels of folate were higher, the researchers found.

While the study underlines the importance of folic acid in pregnancy, there may be such a thing as too much folic acid supplementation, says first author Christine Loftus, an epidemiologist from the environmental & occupational health sciences department at the University of Washington.

“Although supplementation has been shown to be protective against neural tube defects, which are devastating birth defects of the central nervous system, recent research suggests that too much prenatal folic acid may impair healthy fetal neurodevelopment,” Loftus says. “The dose of folic acid is something that pregnant women should discuss with their doctors.”

Researchers have linked long-term exposure to PM10 to reduced lung function and the development of cardiovascular and respiratory diseases. In this study, researchers did not find that other pollutants, including nitrogen dioxide, which is a marker for high-concentration motor traffic, affected IQ.

The authors say that they could not explain how PM10 exposure contributes to lower IQ, but that animal studies indicate that air pollution exposure increases maternal inflammation and oxidative stress.

“This could result in placental inflammation and may interfere with placental or fetal epigenetic programming,” says senior author Kara LeWinn, associate professor of psychiatry at the University of California, San Francisco School of Medicine.

“While it’s beyond the scope of our paper to understand how folate might alter this association, it is possible that higher folate levels increase the antioxidant capability of the diet, buffering oxidative stress associated with PM10 exposure.

“It may also be that folate itself is protective, since it plays an important role in healthy neurodevelopment, regardless of air pollution exposure.”

About the Authors

Additional coauthors are from the University of Washington, UC San Francisco, Vanderbilt University Medical Center, and the University of Tennessee. The National Institutes of Health and the Urban Child Institute supported the work.

Source: University of Washington

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