Pollution, early life stress may be a "double hit" on children's mental health: Study

High exposure to early life stress at home, coupled with elevated prenatal exposure to air pollution, may put children at a higher risk of attention and thought problems, according to a study.

Researchers, including those from Columbia University in the US, said early life stress is common among children from disadvantaged backgrounds, who also often live in areas with greater exposure to air pollution.

The study, published in the Journal of Child Psychology and Psychiatry, assessed the combined effects of air pollution and early life stress on school-age children.

"Prenatal exposure to polycyclic aromatic hydrocarbons (PAH), a neurotoxicant common in air pollution, seems to magnify or sustain the effects of early life social and economic stress on mental health in children," said study first author David Pagliaccio from Columbia University.

The new research analysed data from the CCCEH Mothers and Newborns study conducted in the US, which includes many participants who self-identify as African American or Dominican.

In the study, mothers wore an air monitoring backpack during the third trimester of pregnancy which measured exposure to air pollutants in their daily lives.

The mothers then reported on stress in the lives of their children when they were five years old, along with information on neighbourhood quality, material hardship, intimate partner violence, perceived stress, lack of social support, and general distress levels.

Mothers continued to report on their child's psychiatric symptoms at ages 5, 7, 9 and 11.

The researchers said the combined effect of air pollution and early life stress could be seen across several measures of thought and attention problems at age 11, including obsessive thoughts, and behaviours.

According to the researchers, these effects are linked to PAH-DNA adducts -- a dose-sensitive marker of air pollution exposure.

"Air pollutants are common in our environment, particularly in cities, and given socioeconomic inequities and environmental injustice, children growing up in disadvantaged circumstances are more likely to experience both life stress and exposure to neurotoxic chemicals," said senior author Amy Margolis from Columbia University.

"These exposures have a combined effect on poor mental health outcomes and point to the importance of public health programs that try to lessen exposure to these critical risk factors, to improve not only physical, but psychological health," said Julie Herbstman, another co-author from Columbia University.

According to the study, PAH and early life stress may act as a "double hit" on shared biological pathways connected to attention and thought problems.

The researchers said stress may lead to wide-ranging changes in biological processes like epigenetic expression, stress hormone function, inflammation, and brain function.