A new evidence suggests air pollution is not just associated with asthma and respiratory diseases, but may also impact metabolic and neurological development of children, putting them at an increased risk of anxiety and depression, says a study.

"Recent evidence suggests the central nervous system is particularly vulnerable to air pollution, suggesting a role in etiology of mental disorders, like anxiety or depression," said study lead author Kelly Brunst, Assistant Professor at the University of Cincinnati in the US.

"This is the first study to use neuro-imaging to evaluate exposure to traffic-related air pollution, metabolite dysregulation in brain and generalised anxiety symptoms among otherwise healthy children," Brunst said.

For the study, published in the journal Environmental Research, the researchers evaluated imaging of 145 children at an average age of 12 years, looking specifically at levels of myo-inositol in brain through a specialised MRI technique, magnetic resonance spectroscopy.

Myo-inositol is a naturally-occurring metabolite, mainly found in specialised brain cells known as glial cells, which assists in maintaining cell volume and fluid balance in brain and serves as a regulator for hormones and insulin in the body. Rise in myo-inositol levels correlate with increased population of glial cells, which often occurs in states of inflammation.

Among those exposed to higher levels of traffic-related air pollution, there were significant increases of myo-inositol in brain compared with those with lower pollution exposure, researchers said. They also observed rise in myo-inositol to be associated with more generalised anxiety symptoms. "In the higher, recent exposure group, we saw a 12 per cent increase in anxiety symptoms," said Brunst.

Brunst, however, noted that the observed increase in reported generalised anxiety symptoms in this cohort of typically developing children was relatively small and were not likely to result in a clinical diagnosis of an anxiety disorder.