Air pollution could increase children's risk of developing mental illness, a new study found. Alarmingly, the link persists even in low air pollution levels.

In the new study, researchers found a link between small surges in air pollution rates and the substantial increase in the numbers of psychiatric problems treated.

While it is the first study to establish such association, it adds to the growing research where evidence shows air pollution has significant impacts on the cognitive and mental well-being. These growing evidence also show that children are highly susceptible to poor air quality.

In the new study, the research team from Umeå University in Sweden analyzed the air pollution exposure data of over 500,000 young participants under the age of 18.

The researchers then compared the data with the records of the medications prescribed for the treatment of mental illnesses. These medicines range from simple sedatives all the way to antipsychotics.

"The results can mean that a lower concentration of air pollution, first and foremost from traffic, may reduce psychiatric disorders in children and adolescents," said researcher Anna Oudin who led the research team.

Personally, Oudin added that she would be worried if she lived in an area where air pollution rates are high.

In the United Kingdom, air pollution rates are above the allowed limits in several cities. Annually, there are an estimated 40,000 cases of early deaths linked to air pollution. The causes of death include conditions such as strokes, lung disease and heart attacks.

The World Health Organization and the European Union set a 40mcg/m3 (micrograms per cubic meter) for nitrogen dioxide (NO2). However, in many cities like London, the NO2 rates are often beyond the prescribed limit.

In the study, the team found a mere 10mcg/m3 increase surge in the levels of NO2 was associated with a 9 percent increase in children's mental illness rates.

Moreover, the same amount of increase in tiny particulate matter PM2.5 and PM10 was linked to a 4 percent increase in the mental conditions.

It gets even more alarming. Sweden has relatively low air pollution levels. But even in this country, the study still found the same association even below the 15mcg/m3 levels.

This suggests that more polluted cities carry much higher risks. They also face more challenges as they need to make substantial changes to improve their air quality.

While the study cannot tell what would happen to the mental illness rates in cities with even higher air pollution levels, Oudin made an assumption that it could also rise. In all the air pollution research Oudin had been part of, there seems to be a linear effect in the association.

However, the study does have its limitations and one of which is that it doesn't answer how air pollution increases mental illness in children. Oudin offered a probable mechanism - air pollution causes inflammation when it gets inside the body and the brain. Past research also linked inflammation to a series of psychiatric illness.

"The severe impact of child and adolescent mental health problems on society, together with the plausible and preventable association of exposure to air pollution, deserves special attention," wrote the researchers.

The findings were released in the journal BMJ Open on June 3.

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