TIME Reproductive Health

How Prenatal Pollution Exposure Can Lead to Behavior Problems in Children

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WALTER ZERLA—Getty Images/Cultura RF

The air that expecting moms breathe can have lasting effects on their children, and the latest study details how

It’s no secret that polluted air — from cigarette smoke, cars and burning heating oil — can have a negative impact on our health. But there’s even stronger evidence now about how that air pollution can affect even growing babies in the womb.

In a study published in the Journal of Child Psychology and Psychiatry, researchers led by Amy Margolis at the Columbia Mailman School of Public Health looked for connections between how much exposure an expectant mother has to levels of a primary air pollutant, polycyclic aromatic hydrocarbons (PAHs) and measurements of children’s behavior and emotional states from age three to 11 years. In previous studies, the group showed that higher levels of maternal PAHs at birth were linked to higher rates of anxiety, depression and attention disorders in children at age six and seven years.

MORE: ADHD Linked to the Air Pregnant Women Breathe

In the current study, which follows the same group of children until age 11, the researchers focused on finding an explanation for the connection between PAHs and behavioral issues. They evaluated the children on a standard test of emotional self regulation that captures aggression, impulsiveness, and intensity of emotions. Other studies have linked this ability to self regulate to social competence and the ability to interact with others, a fundamental aspect of many emotional and social behaviors.

Among the 462 children monitored, those whose mothers showed higher levels of PAH at delivery (an indicator of PAH levels during pregnancy), were less likely to regulate their behaviors and emotions at age 9 and 11 than those whose mothers showed lower levels of the pollutant.

MORE: How the First Nine Months Shape the Rest of Your Life

In normal development, children gradually gain the ability to control their emotions and behaviors, learning how to delay gratification, for example, and manage their emotions and not always act on impulse. But the study showed that children whose mothers had higher levels of PAHs during pregnancy didn’t experience this normal trajectory of emotional and social development, which could lead to more high risk behaviors during adolescence, including drug abuse and aggression and violence. Abnormal self-regulation can also lay a foundation for problems in attention and socialization.

“There is a significant association directly between PAH exposure and poorer social competence,” says Frederica Perera, a co-author of the study from Columbia.

MORE: Study: Air Pollution Heightens Risk of Obesity and Diabetes

She and her co-authors believe that the PAHs may be reducing the amount of white matter in the brain; white matter is a measure of how extensive the brain’s nerve network is, and PAH exposure has been linked to compromised connections in areas of the brain associated with behavior and emotion.

Such exposure, however, can be reduced, and some of it is within people’s control. Recent policies to improve air quality in the areas of New York City where the study participants live, for example, are already having an effect. The study, which involves mother-child pairs in northern Manhattan and the south Bronx, is ongoing, and new mothers joining the study are already showing lower levels of PAHs than mothers in the original group. The researchers will continue to follow the original population of children as well, to monitor how long term the effects of the prenatal PAH exposure might be.

But even without policy changes, “the exposures [to PAHs] are preventable,” says Perera. Families can take action to reduce air pollution in their own homes by reducing exposure to cigarette smoke, avoiding wood-burning fireplaces in confined areas, and making sure that cooking areas are well ventilated to reduce filling the home with smoke from burned or charred food.

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