New study in Sweden indicates increased mental illness in children & teenagers exposed to air pollution
A major new study in Sweden has linked worse air pollution to increased mental illness in children, even at low levels of pollution. The research is the first study to establish the link, but is consistent with a growing body of evidence that air pollution can affect mental and cognitive health and that children and adolescents are particularly vulnerable to poor air quality. The suspected mechanism is that air pollution chemicals or small particles breathed in can get into the bloodstream and thus enter the brain. This can cause mild inflammation, and that is associated with a range of psychiatric disorders. The research, published in the peer-reviewed journal BMJ Open, examined the pollution exposure of more than 500,000 under-18s in Sweden and compared this with records of medicines prescribed for mental illnesses, ranging from sedatives to anti-psychotics. Though a relatively crude measure of mental problems, it is a reliable measure. The air pollution (NO2 and particulates) came primarily from traffic. Children are more sensitive and vulnerable to the damage than adults, as they tend to be more active and their brains and organs are still developing. There are confounding factors of poverty, with relatively deprived areas having worse environmental quality, and more studies are needed to corroborate the findings.
Air pollution linked to increased mental illness in children
New research is first to establish the link and builds on other evidence that children are particularly vulnerable to even low levels of pollution
By Damian Carrington @dpcarrington
Monday 13 June 2016
The full study is here
A major new study has linked air pollution to increased mental illness in children, even at low levels of pollution.
The new research found that relatively small increases in air pollution were associated with a significant increase in treated psychiatric problems. It is the first study to establish the link but is consistent with a growing body of evidence that air pollution can affect mental and cognitive health and that children are particularly vulnerable to poor air quality.
The research, published in the peer-reviewed journal BMJ Open, examined the pollution exposure of more than 500,000 under-18s in Sweden and compared this with records of medicines prescribed for mental illnesses, ranging from sedatives to anti-psychotics.
“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 Anna Oudin, at Umeå University, who led the study. “I would be worried myself if I lived in an area with high air pollution.”
Prof Frank Kelly, at King’s College London, said the research was important. “This builds on existing evidence that children are particularly sensitive to poor air quality probably because their lifestyles increase the dose of air pollution they are exposed too – ie they are more active – and that developing organs may be more vulnerable until they fully mature.”
Air pollution in the UK is above legal limits in many cities and estimated to cause 40,000 early deaths a year, though this only includes illnesses such as lung disease, heart attacks and strokes.
The EU and WHO limit for nitrogen dioxide (NO2) is 40mg/m3, but levels can reach many times that in polluted cities like London. The researchers found that a 10mg/m3 increase in NO2 corresponded to a 9% increase in mental illness in the children. For the same increase in tiny particulate matter (PM2.5 and PM10), the increase was 4%.
One striking aspect of the new research is that Sweden has low levels of air pollution, but the researchers still saw the link even below levels of 15mg/m3. “Sweden is not a country that suffers from very bad air quality, said Kelly. “This suggests that other countries and cities have an even bigger challenge, as they will have to make significant improvements to their air quality so that it is even cleaner than Sweden’s.”
It is not possible to say from this study what would happen to rates of mental illness at higher levels of air pollution, but Oudin said they could rise: “In all the air pollution studies I have been involved in, the effects seem to be linear.”
This type of research cannot prove a causal link between the air pollution and increases in mental illness, but there is a plausible mechanism. “We know air pollution can get into bodies and brains and cause inflammation,” said Oudin. Animal studies indicate that inflammation is associated with a range of psychiatric disorders.
There have also been several earlier studies that found associations between air pollution and autism spectrum disorders and learning and development in children. “This study adds to evidence that air pollution may have detrimental effects on the brains of children and adolescents,” the Swedish researchers said.
In May, the Guardian revealed an unpublished air pollution report that demonstrated that 433 schools in London are located in areas that exceed EU limits for NO2 pollution and that four-fifths of those are in deprived areas.
In May, a WHO report concluded that air pollution was rising at an “alarming rate” in the world’s cities, while a report in September found 3 million people a year suffer early deaths around the world from air pollution.
The new Swedish paper concludes: “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.”
The study’s Abstract says:
Objective To investigate associations between exposure to air pollution and child and adolescent mental health.
Design Observational study.
Setting Swedish National Register data on dispensed medications for a broad range of psychiatric disorders, including sedative medications, sleeping pills and antipsychotic medications, together with socioeconomic and demographic data and a national land use regression model for air pollution concentrations for NO2, PM10 and PM2.5.
Participants The entire population under 18 years of age in 4 major counties. We excluded cohort members whose parents had dispensed a medication in the same medication group since the start date of the register. The cohort size was 552 221.
Main outcome measures Cox proportional hazards models to estimate HRs and their 95% CIs for the outcomes, adjusted for individual-level and group-level characteristics.
Results The average length of follow-up was 3.5 years, with an average number of events per 1000 cohort members of ∼21. The mean annual level of NO2 was 9.8 µg/m3. Children and adolescents living in areas with higher air pollution concentrations were more likely to have a dispensed medication for a psychiatric disorder during follow-up (HR=1.09, 95% CI 1.06 to 1.12, associated with a 10 µg/m3 increase in NO2). The association with NO2 was clearly present in 3 out of 4 counties in the study area; however, no statistically significant heterogeneity was detected.
Conclusion There may be a link between exposure to air pollution and dispensed medications for certain psychiatric disorders in children and adolescents even at the relatively low levels ofair pollution in the study regions. The findings should be corroborated by others.
In terms of looking at confounding variables, the study says in its Introduction:
Perceived environmental noise and low air quality have been linked to mental health outcomes in adults such as depression.17
Epidemiological studies have shown that living in areas with elevated concentration of air pollution is linked with decreased cognitive function,18–23
Furthermore, children in Spain who attended schools with higher traffic-related air pollution have been observed to have a smaller improvement in cognitive development than children who attended schools with lower traffic-related air pollution.33
In a review from 2012 on epidemiological studies on neuropsychological effects of air pollution, the authors conclude that there is evidence for air pollution to be associated with mental development and mental decline.34
The National Institute of Environmental Health Sciences/National Institute of Health has convened an expert panel to identify research gaps and priority goals in the field of air pollution and mental disorders such as depression,3 and expressed the need for well-designed studies with good data on exposure, outcomes and possible confounders or mediators of effect.3
They were highlighting several methodological challenges when investigating air pollution and brain health. For example, parental mental health could influence exposure via socioeconomic status since there are often strong associations between socio economy and air pollution levels.
It has been argued that socially disadvantaged people tend to be segregated in relatively deprived areas with a worse environmental quality,35 ,36 and there are often strong socioeconomic gradients in mental health.37
Social characteristics may therefore modify the association between air pollution and mental health and also act as a major confounder. There is little consensus on the causal relationship between urbanisation and mental health, but it seems as if urban and rural environments can have pernicious and salutary consequences on mental health.38
Factors with strong urban–rural gradients related to the environment such as air pollution concentrations are often neglected as a possible cause of mental health problems.
Neighbourhood poverty has, for example, been observed to affect mental health in children,39 but there were no adjustments done for neighbourhood air pollution concentrations.
The conclusion of the study:
Conclusions and implications
“In Sweden, the societal cost for mental disorders has been estimated to be 2% of Gross Domestic Product (GDP). The onset is often in adolescence or young adulthood. Remission is not always possible and for many, symptoms persist despite use of treatments. If confirmed, our findings implicate that there may be a link between exposure to air pollution and dispensed medications for certain psychiatric disorders in children and adolescents.”