Air Pollution During Pregnancy Increases the Risk of Mental Health Problems

A baby’s exposure to air pollution in the womb is linked to the development of certain mental health problems once the child reaches adolescence, new research has found. The University of Bristol-led study, published in JAMA Network Open, looked at the long-term effects of early childhood exposure to air pollution and noise on mental health.

How Particulate Matter Exposure During Pregnancy and Childhood Affects Mental Health

There is growing evidence that air pollution, which consists of toxic gases and particulate matter, may contribute to the onset of mental health problems. It is thought that pollution could negatively affect mental health through numerous pathways, including compromising the blood-brain barrier, promoting neuroinflammation and oxidative stress, and directly entering the brain and damaging tissue.

Although adolescence is a key period for the onset of these problems, relatively few studies have examined the relationship between air and noise exposure in early childhood and mental health. In this new study, the researchers investigated the long-term effects of air and noise exposure during pregnancy, early childhood and adolescence on three common mental health problems: psychotic experiences (including hallucinations, such as hearing or seeing things that others cannot see, and delusions, such as highly paranoid thoughts), depression and anxiety.

To investigate this, the team used data from over 9,000 participants in the Bristol birth cohort study Children of the 90s (also known as the Avon Longitudinal Study of Parents and Children), which recruited over 14,000 pregnant women from the Bristol area between 1991 and 1992 and has since followed the lives of the women, their children and their partners. By linking the participants’ early childhood data with their reports of their mental health at the ages of 13, 18 and 24, the researchers were able to use this data to map outdoor air and noise pollution in South West England at different points in time.

The researchers found that relatively small increases in particulate matter exposure during pregnancy and childhood were associated with more psychotic experiences and symptoms of depression many years later in teenage and early adulthood. These associations persisted even after accounting for numerous related risk factors, such as family history of psychiatric illness, socioeconomic status and other area-level factors such as population density, deprivation, green space and social fragmentation.

Air Pollution: Measures to Reduce Exposure

The team found that each 0.72 micrograms per cubic meter increase in particulate matter (PM2.5) exposure during pregnancy and childhood was associated with an 11 percent and 9 percent increased likelihood of psychotic experiences, respectively, while exposure during pregnancy was associated with a 10 percent increased likelihood of depression. In contrast, higher noise exposure during childhood and teenage years was associated with more anxiety symptoms later on.

According to the study’s lead author, Dr. Joanne Newbury, childhood, adolescence and early adulthood are critical periods for the development of psychiatric disorders: Worldwide, almost two-thirds of sufferers become ill by the age of 25. These findings add to a growing body of evidence – from different populations, in different locations and with different study designs – suggesting a detrimental impact of air pollution (and possibly noise pollution) on mental health.

As air pollution is also an avoidable burden, measures to reduce exposure, such as the establishment of low emission zones, could improve mental health. Targeted measures for vulnerable groups such as pregnant women and children could also provide an opportunity for a faster reduction in exposure. It is important to emphasize that these results do not in themselves prove a causal relationship. However, other recent studies have shown that low emission zones appear to have a positive effect on mental health.