Exposure to air pollution linked with poor mental health

A baby’s exposure to air pollution while in the womb is associated with the development of certain mental health problems once the infant reaches adolescence, according to new UK research.

Growing evidence suggests air pollution, which comprises toxic gases and particulate matter, might contribute to the onset of mental health problems. It is thought that pollution could negatively affect mental health via numerous pathways — including by compromising the blood–brain barrier — promoting neuroinflammation and oxidative stress, and directly entering the brain and damaging tissue. But despite youth being a key period for the onset of these problems, until now, relatively few studies have investigated the associations of air and noise exposure during early life with mental health.

In a new study led by the University of Bristol, researchers sought to examine the long-term impact of air and noise pollution exposure during pregnancy, early childhood and adolescence on three common mental health problems: psychotic experiences, depression and anxiety. To investigate this, the team used data from over 9000 participants from Bristol’s Children of the 90s birth cohort study (also known as the Avon Longitudinal Study of Parents and Children), which recruited over 14,000 pregnant women from the Bristol area in the early 1990s and has followed the lives of these women, their children and their partners ever since.

By linking participants’ early childhood data with their mental health reports at the ages of 13, 18 and 24 years, researchers were able to use this to map against outdoor air and noise pollution in South West England at different time points. Their results were published in JAMA Network Open.

Researchers found that relatively small increases in fine particulate matter during pregnancy and childhood were associated with more psychotic experiences and depression symptoms many years later in teenage years and early adulthood. These associations persisted after considering many related risk factors, such as family psychiatric history, socioeconomic status and other area-level factors such as population density, deprivation, greenspace and social fragmentation.

The team found that every 0.72 mg/m³ increase in fine particulate matter (PM_2.5) during pregnancy and childhood was associated with an 11% increased odds and 9% increased odds for psychotic experiences, respectively; while exposure in pregnancy was associated with a 10% increased odds for depression. In contrast, higher noise pollution exposure in childhood and teenage years was subsequently associated with more anxiety symptoms.

“Childhood, adolescence and early adulthood are critical periods for the development of psychiatric disorders: worldwide, nearly two-thirds of those affected become unwell by the age of 25,” said Bristol’s Dr Joanne Newbury, the study’s lead author. “Our findings add to a growing body of evidence — from different populations, locations and using different study designs — suggesting a detrimental impact of air pollution (and potentially noise pollution) on mental health.

“This is a major concern, because air pollution is now such a common exposure, and rates of mental health problems are increasing globally. Given that pollution is also a preventable exposure, interventions to reduce exposure, such as low emissions zones, could potentially improve mental health. Targeted interventions for vulnerable groups including pregnant women and children could also provide an opportunity for more rapid reductions in exposure.

Newbury acknowledged that these findings, by themselves, do not prove a causal association. However, they come just weeks after a separate study — presented at ESC Preventive Cardiology 2024 — found that air pollution is linked with stress and depression, putting under-65-year-olds at increased risk of dying from cardiovascular disease.

To conduct the US-based study, county-level data on annual PM_2.5 levels were obtained from the Centers for Disease Control and Prevention (CDC). The researchers gathered data on the average number of days that county residents experienced mental health issues — including stress, depression and emotional problems — from the CDC; each county was then categorised into three groups based on these numbers. Age-adjusted premature cardiovascular mortality rates (under 65 years of age) for each county were also obtained from the CDC.

The study included 3047 US counties, representing 315,720,938 residents in 2013. Between 2013 and 2019, some 1,079,656 (0.34%) participants died from cardiovascular disease before the age of 65 years. The researchers analysed the associations between pollution, mental health and premature cardiovascular mortality after adjusting for factors that could influence the relationships.

Counties with dirty air (high PM_2.5 concentrations) were 10% more likely to report high levels of poor mental health (PMH) days compared to counties with clean air (low PM_2.5 concentrations) — and that risk was markedly greater in counties with a high prevalence of minority groups or poverty. The link between PMH and premature cardiovascular mortality was meanwhile strongest in counties with higher levels (≥10 µm²) of air pollution. In these counties, higher levels of PMH were associated with a three-fold increase in premature cardiovascular mortality compared to lower PMH levels. Further, one-third of the pollution-related risk of premature cardiovascular deaths was explained by increased burden of PMH.

“Our results reveal a dual threat from air pollution: it not only worsens mental health but also significantly amplifies the risk of heart-related deaths associated with poor mental health,” said lead author Dr Shady Abohashem, of Harvard Medical School. “Public health strategies are urgently needed to address both air quality and mental wellbeing in order to preserve cardiovascular health.”

Image credit: iStock.com/pcess609