New US study strengthens link between child brain development and air pollution

Evidence is growing of a tangible link between city air pollution and how a child’s brain develops, including implications for possible behavioural problems.

Researchers in the USA are the latest to draw attention to how toxic fumes like nitrogen dioxide in the environment, when exposed to pregnant women, can linger long after a child’s birth and affect their development.

A new study by the University of Washington has found that children whose mothers, while expecting, experienced higher nitrogen dioxide (NO2) exposure, particularly in the first and second trimester, were more likely to have behavioral problems. Interestingly, boys were more likely to be affected in the second part of a pregnancy.

The study, published in Environmental Health Perspectives, also showed that higher exposures to small-particle air pollution (PM2.5) when children were two to four years old was associated with poorer child behavioral functioning and cognitive performance.

‘Implications for behavioral problems’

Yu Ni, lead author and a postdoctoral scholar in the Department of Environmental & Occupational Health Sciences, said: “Even in cities like Seattle or San Francisco, which have a lot of traffic but where the pollution levels are still relatively low, we found that children with higher prenatal NO2 exposure had more behavioral problems, especially with NOexposure in the first and second trimester.”

The study involved almost 2,000 mothers recruited during pregnancy from six cities: Memphis, Tennessee; Minneapolis; Rochester, N.Y.; San Francisco; and two in Washington, Seattle and Yakima. Originally, these participants were enrolled as part of three separate studies: CANDLEGAPPS and TIDES.

The three studies have been combined under a major NIH initiative called ECHO, which brings together multiple pregnancy cohorts to address key child health concerns. These three combined cohorts are known as the ECHO PATHWAYS consortium.

The study employed a state-of-the-art model of air pollution levels in the United States over time and space that was developed at the University of Washington. Using participant address information, the researchers were able to estimate each mother and child’s exposures during the pregnancy period and early childhood.

Exposure to NO2 and PM2.5 pollution in early life is important to understand, Ni said, because “there are known biological mechanisms that can link a mother’s inhalation of these pollutants to effects on placenta and fetal brain development.”

‘Critical time of ongoing brain development’

Researchers say the first few years are a ‘critical time of ongoing brain development’, as the number of neural connections explodes and the brain reaches 90 per cent. of its future adult size, the researchers write. And for young children in particular, inhaled pollutants that invade deep in the lung and enter the central nervous system can cause damage in areas relevant for behavioral and cognitive function.

Dr. Catherine Karr, senior author and a professor in the UW School of Public Health and School of Medicine, said: “This study reinforces the unique vulnerability of children to air pollution – both in fetal life where major organ development and function occurs as well as into childhood when those processes continue.

These early life perturbations can have lasting impacts on lifelong brain function. This study underscores the importance of air pollution as a preventable risk factor for healthy child neurodevelopment,” said

Researchers found that exposure to PM2.5 pollution was generally associated with more behavioral problems in girls than boys, while the negative effects of PM2.5 exposure in the second trimester was stronger in boys.

“We hope the evidence from this study will contribute to informed policymaking in the future,” added Yu Ni said. “In terms of reducing air pollution, the U.S. has gone a long way under the Clean Air Act, but there are threats to continued improvement in the nation’s air quality. The evidence suggests there is reason to bring the level of air pollution down even further as we better understand the vulnerability of pregnant women and children.”

Click here for more on the study.

Author: Simon Weedy

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