Children exposed to high levels of air pollution are up to 50 per cent more likely to self-harm later in life, a study has suggested.
A study of 1.4million kids under 10 in Denmark revealed those exposed to a high level of nitrogen dioxide were more likely to self harm in adulthood than their peers.
And people in the same age group exposed to above average levels of fine particulate matter (PM2.5) were 48 per cent more likely to subsequently self-harm.
Nitrogen dioxide is mainly produces by cars, while PM2.5 is mainly emitted by burning diesel and petrol, which is most commonly used for shipping and heating.
These two pollutants are among those most commonly linked with causing harm to physical health, such as heart and lung diseases, by getting into the bloodstream and causing inflammation.
Researchers are yet to explain the mechanism for how these pollutants can cause mental health problems.
But they suggested high pollution levels could trigger inflammation in the brain, leading to mental health problems.
Childhood is a ‘sensitive time for brain development’, so youngster may be ‘particularly susceptible’ to negative effects from toxic particle in the air, they added.
Children exposed to high levels of common air pollutants nitrogen dioxide and particulate matter are up to 50 per cent more likely to self-harm later in life, a study by researchers in the UK and Denmark has found
Researchers at the University of Manchester in England and Aarhus University in Denmark looked at national databases to track 1.4million Danes born between 1979 and 2006.
The study, which was published in Preventive Medicine, used each person’s place of residence from birth to their 10th birthday and how long they stayed at that address to measure outdoor levels of particulate matter and nitrogen dioxide.
They then tracked the individuals until December 2016, noting which ones went to hospital for self-harm.
They classified self-harm as overdosing and arm cutting, or any other intentional harm.
What is particulate matter and nitrogen dioxide?
Particulate matter (PM) is everything in the air that is not a gas.
It consists of a huge variety of chemicals and materials, some of which can be toxic.
Due to the small size of many of the particles that form PM some of these toxins can enter the bloodstream and be transported around the body, lodging in the heart, brain and other organs.
Therefore, exposure to PM can result in serious impacts to health, especially in vulnerable groups of people such as the young, elderly, and those with respiratory problems.
Meanwhile, nitrogen dioxide (NO2) is a gas mainly produced during the combustion of fossil fuels.
Short-term exposure to concentrations of NO2 can cause inflammation of the airways and increase susceptibility to respiratory infections and to allergens.
NO2 can exacerbate the symptoms of those already suffering from lung or heart conditions.
Source: Department for Environment Food & Rural Affairs
Some 32,984 people (2.3 per cent) harmed themselves in the study period, with cases higher among women, those whose parents had mental illness and individuals from poorer families.
Exposure to an average of 19 μg/m3 or more of particulate matter each day was associated with a 48 per cent higher chance of self-harming later in life, compared to children exposed to an average of 13 μg/m3 per day or less.
And for every 5 μg/m3 increase in exposure above 19 μg/m3, the risk of self harm rose by 42 per cent.
The researchers looked at particulate matter that is less than 2.5 micrometers in diameter.
The average daily exposure to particulate matter was 13.5 μg/m3 per day.
UK air quality standards require concentrations of this size of particulate matter not to exceed an annual average of 25 μg/m3.
Meanwhile, children who were exposed to an average of 25 μg/m3 or more of nitrogen dioxide between birth and 10-years-old were were 50 per cent more likely to self-harm than those who were in areas where they came into contact with less than 10 μg/m3 or less per day.
And for every 10 μg/m3 increase above 25 μg/m3, the risk of self-harm rose by 21 per cent.
The average daily exposure to nitrogen dioxide was 18.1 μg/m3 per day.
Air quality rules in the UK outline that annual average concentrations of nitrogen dioxide must not exceed 40 μg/m3.
Lead author Dr Pearl Mok, a research fellow at Manchester University said the research is the first population-based study to reveal that long-term exposure to two common pollutants during childhood, is associated with higher self-harm risks.
She said: ‘Our findings add to the growing evidence-base indicating that higher levels of air pollution exposure are linked with poor mental health outcomes.
‘Although air pollution is widespread, it is a modifiable risk factor and we therefore hope our study’s findings will inform policymakers who are devising strategies to combat this problem.’
The findings follow a study from China, which discovered that children who attended schools with higher daily concentrations of particulate matter had more cases of self-harm than those who went to schools in areas where the air was less polluted.
But that study didn’t spot any links between self-harm and nitrogen oxide.
Professor Roger Webb, a psychology and mental health expert at Manchester University and a co-author on the study said: ‘A growing body of evidence in recent years has indicated that exposure to air pollution is also associated with adverse mental health outcomes.
‘Children living in neighbourhoods with higher levels of air pollution have been reported to have increased risks of developing a range of psychiatric disorders including schizophrenia, depression, and attention-deficit hyperactivity disorder (ADHD).
‘Though the mechanisms linking air pollution and development and exacerbation of mental disorders or its associated distress have not yet been explained, it has been well-established that it can cause inflammation and oxidative stress.
‘This study is the first to provide valuable evidence on the association between childhood exposure to air pollution and subsequently elevated self-harm risk.
‘However, further research is needed to investigate to what degree our findings can be generalised to other countries, especially lower- and middle-income countries where levels of ambient air pollution are far higher than they are in Denmark.’