Air Pollution Can Lead to Adverse Birth Outcomes and Impair Children's Brain Development

A new study led by the Harvard T.H. Chan School of Public Health has found an association between exposure to fine particulate matter (PM2.5) and altered immune responses in pregnant women that may lead to adverse birth outcomes. The study is the first to examine the link between PM2.5 and maternal-fetal health at the single-cell level and to demonstrate the health risk of PM2.5 exposure for pregnant women. The study was published in Science Advances.

“This study represents a major advance in our understanding of the biological pathways through which PM2.5 exposure affects pregnancy, maternal health, and fetal development. Its advanced methodology represents a significant innovation for studying immune responses to environmental exposures,” said corresponding author Kari Nadeau, John Rock Professor of Climate and Population Studies and Chair of the Department of Environmental Health. Previous research has found links between exposure to PM2.5 and maternal and child health complications, including preeclampsia, low birth weight, and developmental delays in early childhood.

Minimizing Air Pollution for Pregnant Women

To understand these links at the cellular level, the researchers used air quality data collected by the U.S. Environmental Protection Agency to calculate the average PM2.5 exposure of the study participants. The participants were both non-pregnant women and women at 20 weeks pregnant. The researchers then used an innovative technology to understand how pollution altered the DNA of each of the participants’ cells. In each cell, they were able to map changes to histones, the proteins that control the release of cytokines – proteins that control inflammation in the body and can affect pregnancy.

The study found that PM2.5 exposure can affect the histone profiles of pregnant women by disrupting the normal balance of cytokine genes and leading to increased inflammation in both women and fetuses. In pregnant women, this increased inflammation may be associated with adverse pregnancy outcomes. “Our findings underscore the importance of minimizing air pollution for pregnant women to protect maternal and fetal health,” said co-author Youn Soo Jung, a research scientist in the Division of Environmental Health. Policy measures to improve air quality, as well as clinical guidelines to help pregnant women reduce their exposure to pollutants, could have a direct impact on reducing pregnancy complications, according to the researchers.

How Air Pollution Affects Children’s Neurological Development

Exposure to certain pollutants such as particulate matter (PM2.5) and nitrogen oxides (NOx) during pregnancy and childhood is associated with differences in the microstructure of the white brain matter, and some of these effects persist throughout adolescence. These are the main conclusions of a study led by the Barcelona Institute for Global Health (ISGlobal), a center supported by the “la Caixa” Foundation. The results, published in Environmental Research, underscore the importance of addressing air pollution as a public health issue, particularly for pregnant women and children.

There is a growing body of evidence showing that air pollution affects the neurological development of children. Recent studies have used brain imaging to examine the effects of air pollutants on brain white matter, which plays a crucial role in connecting different brain regions. However, these studies were limited in that they only looked at one point in time and did not follow participants throughout their childhood.

The study included over 4,000 participants who had been followed since birth as part of the Generation R study in Rotterdam, the Netherlands. The research team estimated exposure to 14 different air pollutants during pregnancy and childhood based on the location of the families’ homes. For 1,314 children, the researchers were able to examine changes in the microstructure of the white matter using data from two brain scans – one at around 10 years of age and one at around 14 years of age.

Some Effects Persist, Others Decrease Over Time

The analysis indicated that exposure to certain pollutants, such as particulate matter (PM_2.5) and nitrogen oxides (NO_x), was associated with differences in the development of white matter in the brain. Specifically, higher exposure to PM_2.5 during pregnancy and higher exposure to PM_2.5, PM₁₀, PM_2.5-10 and NO_x during childhood were associated with lower levels of a measure called fractional anisotropy, which measures how water molecules diffuse in the brain. In more mature brains, water flows in one direction rather than all directions, resulting in higher values for this marker. This association persisted throughout adolescence (i.e., was also observed at the second scan), suggesting a long-lasting effect of air pollution on brain development. Each increase in air pollution corresponded to a delay of more than five months in the development of fractional anisotropy.

The study also found that some pollutants were associated with changes in another measure of white matter, called mean diffusivity. This reflects the integrity of the white matter and tends to decrease as the brain matures. Higher exposure to pollutants such as silicon in particulate matter (PM_2.5) during pregnancy was associated with initially higher mean diffusivity, which then decreased more rapidly with increasing age of the children. This suggests that some effects of air pollution may fade over time.

Overall, the study suggests that exposure to air pollution during both pregnancy and early childhood can have lasting effects on the brain’s white matter. Importantly, these results were present in children exposed to PM_2.5 and PM₁₀ concentrations above the current WHO recommended limits, but below the current European Union recommended limits. This supports the need for stricter European guidelines on air pollution, which the researchers expect to be adopted soon by the European Parliament.