The more a child is exposed to air pollution, the more likely they are to experience a mental health issue later in life, new research suggests.
The link has been suggested by researchers from King's College London and Duke University in the US, who say that air pollution seems to be as harmful to mental health as lead exposure.
The team analysed 25 year's worth of data from the Environmental-Risk Longitudinal Twin Study, which followed 2232 twin children until their 18th birthday and recorded any exposure to environmental risk factors.
Researchers discovered higher rates of mental health illness symptoms in those exposed to greater levels of air pollutants – such as nitrogen oxide – during childhood and adolescence.
According to the study authors, the influence of air pollution on mental health appears to be modest compared with other factors such as family genetics, yet it remains significant enough to impact brain development.
“This study has demonstrated that children growing up in our biggest cities face a greater risk of mental illness due to higher levels of traffic," says Dr Helen Fisher, the study’s principal investigator and co-author.
Air pollutant exposure for each participant was measured at 10 and 18 years of age based on air pollution levels recorded in the area they lived.
In particular, researchers looked at exposure to nitric oxides (NOx) and particulate matter (PM) – two forms of air pollutant linked to the development of central nervous system diseases.
Once participants turned 18 years old, they were assessed for signs of various psychiatric disorders, including depression, anxiety, schizophrenia and ADHD.
Those consistently exposed to greater levels of air pollutants as children and adolescents displayed poorer mental health at the transition into adulthood, or had a higher 'p-factor' score.
The study also revealed that 22% of participants were exposed to nitrogen oxide levels that exceeded World Health Organization (WHO) guidelines, while 84% had a high exposure to PM2.5 – one of the two most dangerous air pollutants to human life.
Although an observational study, meaning researchers observed participants and recorded any changes with little to no interference, the results stayed the same even after adjusting for other risk factors.
The new findings are also unique with regards to the number of psychiatric disorders investigated, compared with previous studies that have demonstrated links between air pollution and specific mental health disorders.
"These results collectively suggest that youths persistently exposed to moderate levels of NOx air pollution may experience greater overall liability to psychiatric illness by young adulthood — a liability independent of other individual, family, and neighbourhood influences on mental health," say the study authors.
To read the full study paper, click here.
Written by Sylvie Ward
News reporter for Talking Mental Health