Pregnant Moms Who Breathe Dirty Air Have Children With Lower IQs, Study Finds

2 min
This photo taken in June 2013 shows a pregnant woman with a face mask walking on the street in Singapore. That month Singapore's smog index hit the critical 400 level, making it potentially life-threatening to the ill and elderly people, according to a government monitoring site.  (ROSLAN RAHMAN/AFP/Getty Images)

A new study focusing on mothers who breathe soot-laden air adds to a growing body of research into how air pollution affects cognitive development.

Fine particles of pollution, small enough to breathe deep into lungs, come from coal plants, burning fuel in cars and trucks, and airborne dust. Pregnant women exposed to more of this pollution had children with lower IQs compared to women who breathed cleaner air, according to new analysis published in the journal Environmental Research.

The study focused on a group of Tennessee mothers who researchers began to monitor while they were pregnant. As their children grew, researchers gave the kids IQ an test.

“It’s a very long battery that poor small children have to sit through,” says Kaja LeWinn, one of ten research team members and professor of psychiatry at UCSF. “It’s a long time to have a four-to-five year old sitting still.”

Children of mothers exposed to the worst soot pollution scored lower on IQ tests by about two-and-a-half points compared to mothers in cleaner neighborhoods.

“[Fine particulate] pollution is less well-studied as a neurodevelopment toxicant, so I think that makes it particularly interesting to have these results,” says Catherine Karr, a study author and pediatric environmental medicine doctor at the University of Washington.

Visitors gather on a path in Los Angeles' Griffith Park in July 2019 on a day of high air pollution. (Mario Tama/Getty Images)

Unlike many cities in California, Memphis tends to meet federal pollution standards for most days of the year.

Nutrition vs. Air Pollution?

“I think this work really highlights that low-level exposure might be important and that we need to do more work to know what a safe level is,” says Megan Herting, a neuroscientist at USC who was not involved in the research.

Herting says the work does a good job controlling for other factors that might influence cognitive development, like family economics. “It really narrows down and says there’s something about air quality that seems to be driving this decrease.”

The research team also has found something novel: evidence that nutrition buffers the impacts of air pollution. Pregnant women are told to eat foods rich in folate like leafy greens and citrus, or take prenatal vitamins, like folic acid.

“Women with the lowest folate levels, for their children the association between our measure of air pollution and IQ was much stronger,” LeWinn says.

The children of mothers who breathed dirtier air and carried less folate in their bodies scored about seven points lower on IQ tests than children in the top cohort.

“The effect there was about twice as strong as what we saw in the full sample,” she says.

LeWinn and other authors acknowledge the folate results haven’t been replicated. But they say that their work can help identify groups of mothers more vulnerable to pollution’s ill effects. Though doctors already recommend folate as a preventative measure against birth defects, among the cohort of mothers in Tennessee, researchers saw that not all pregnant women took enough of it.

“We as individuals might have ways to better our own outcomes of ourselves and our children,” Herting says. “This suggests that’s going to really help offset some of these other things we might not be able to control.”

Researchers in this area stress they don’t yet know the exact way air pollution might affect the brain.

The California Air Resources Board points out that air pollution may affect brains directly and indirectly, but also says that associations between air pollution and the brain are “just beginning to emerge.”

In recent years, scientists have been amassing evidence connecting air pollution to neurodevelopmental impacts. Last summer, research focused on China found that polluted air is linked to lower intelligence in adults, and worsens with age. A study published in The Lancet found that people living near busy roads in Ontario, Canada were more likely to be diagnosed with dementia, though whether that’s a consequence of respiratory and cardiac problems remains unclear.

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