Higher rates of depression and suicide noticed in people living with air pollution, found by a systematic review of global data.
The research suggests that millions of people could be prevented from becoming depressed by cutting air pollution to the EU’s legal limit worldwide. It assumed that exposure to toxic air is resulting in these cases of depression. Although scientists believe this is likely, however difficult to prove beyond doubt.
The study analyzed the particle pollution that is produced by burning fossil fuels in vehicles, homes, and industry. According to researchers, the new evidence has strengthened the calls to tackle the “silent public health emergency” of dirty air as called by the World Health Organization.
“We’ve shown that air pollution could be causing substantial harm to our mental health, making the case for cleaning up the air we breathe even more urgent,” said Isobel Braithwaite, at University College London (UCL), who led the research.
A significant difference could be made by meeting the EU limit, she said. “You could prevent about 15% of depression, assuming there is a causal relationship. It would be a very large impact, because depression is a very common disease and is increasing.” People diagnosed with depression have crossed 264 million, according to the WHO.
“We know that the finest particulates from dirty air can reach the brain via both the bloodstream and the nose, and that air pollution has been implicated in increased [brain] inflammation, damage to nerve cells and to changes in stress hormone production, which have been linked to poor mental health,” Braithwaite said.
Joseph Hayes, also at UCL and part of the research team, said: “The evidence is highly suggestive that air pollution itself increases the risk of adverse mental health outcomes.”
The research, published in the journal Environmental Health Perspectives, followed strict quality criteria while selecting and collecting research data from 16 countries published up to 2017. A strong statistical link between toxic air and depression and suicide revealed from this. This is supported by more recent research, including studies that linked air pollution with “extremely high mortality” in people with mental disorders and a quadrupled risk of depression in teenagers.
Other research indicates a “huge” reduction in intelligence due to air pollution and is linked to dementia. Earlier in 2019, a comprehensive global review disclosed that air pollution may be damaging every organ and virtually every cell in the human body.
The data analyzed in new research found a link between the depression and air pollution particles smaller than 2.5 micrometers (equivalent to 0.0025 millimeters and known as PM2.5). Exposure to an increase of 10 micrograms per cubic meter (µg/m3) in the level of PM2.5 for a year or more caused a 10% higher risk of getting depression in people. Levels of PM2.5 in cities range from as high as 114µg/m3 in Delhi, India, to just 6µg/m3 in Ottawa, Canada.
In 2017, in the cities of the UK, the average PM2.5 level was 13µg/m3. The researchers estimated that depression in city dwellers could be reduced by about 2.5% by lowering this level to the WHO recommended limit of 10µg/m3.
The data available on suicide risk was for particles ranging up to 10 micrometers (PM10). The researchers found a short-term effect; the risk of suicide increased by 2% with a 10µg/m3 increase over three days.
As more than 90% of the global population is exposed to air pollution above WHO-recommended levels, small increases in risk can still cause harm to many people, scientists say. “This is something everyone is exposed to, so at the population level it is potentially concerning,” said Braithwaite.
Although the results show strong correlations, proving a causal link is difficult for the research as ethical experiments cannot expose people deliberately to harm. Many factors, including the location of the home, education, employment, income, obesity, and smoking, are taken into account in the studies that might affect mental health. However, the potential impact of noise, which often occurs alongside air pollution, was not possible to be separated and is known to have psychological effects.
“This is a comprehensive review over a 40-year period,” said Ioannis Bakolis, at King’s College London, not part of the research team. “Although the studies included were from different parts of the world – eg, China, the US, Germany – and varied in sample size, study design and measures of depression, the reported associations were very similar.”
But according to him, the evidence was limited, and it needed more research. By understanding the impact of the reduction of pollution on mental health, policymakers would get further proof of the benefits of action.
“We all need to do what we can to reduce our own contribution to air pollution, whether that is walking or cycling,” said Braithwaite. “But we also need to be thinking about system change, meaning [government] policies that help reduce overall air pollution levels.” The researchers said it required walking, cycling, and more green spaces to cut air pollution and also improving mental health.
In the UK and Republic of Ireland, the Samaritans can be contacted on 116 123. In the US, the National Suicide Prevention Lifeline is 1-800-273-TALK. In Australia, the crisis support service Lifeline is on 13 11 14.