By Rowenna Hoskin | Science Editor
Before modern medicine, doctors prescribed fresh countryside air as a solution to many illnesses. According to new research, this prescription may not actually be as unscientific as it sounds; a recent overview of studies has found that depression and suicide may be linked to pollution levels.
Pollution has been studied in relation to physical illness such as asthma, cardiovascular damage and even nervous system damage but its effects on mental health are relatively understudied.
Isobel Braithwaite at University College of London and her colleagues looked at 25 studies published up to the end of 2017; upon meta-analysing the data, the team distinguished clear links between pollution levels and the risk of depression and suicide.
To quantify pollution levels the team used particulate matter (PM); PM2.5 refers to particles or liquid droplets in the air that have a diameter less that 2.5 micrometres. Some are naturally occurring like sea salt and dust, or manmade such as particulates from vehicle exhausts.
The World Health Organisation (WHO) guidelines of PM2.5s should not exceed 10 micrograms per cubic metre of air (µg m-3) an average over a year. This is the average level in the UK, while London is higher at 13.3µg m-3, and Delhi is even higher at 133µg m-3.
The UK government’s Committee on the Medical Effects of Air Pollution (COMEAP) estimate that exposure to PM2.5 contributes to 29,000 premature deaths in the UK every year, these refer to deaths from illness. This figure does not take into account the deaths caused from mental health related issues.
The team found that short term exposure to larger levels of pollution (exceeding 10µg m-3) is associated with increased risks of suicide. With each 10µg m-3 increase in PM10 a person was exposed to during a three day period is linked to a 2% increase in risk of suicide.
Braithwaite says that the links between pollution and mental health is of the upmost importance as there is still so much work left to do to reduce air pollution:
“Knowing [pollution levels] not only affects physical health but it could also be affecting our mental health, which is something that does affect large numbers of people, I think it adds to the weight of the argument for cleaner air and policies that achieve it,”
Research on the links pollution has on mental health is decades behind the research into its effects on physical health. Braithwaite predicts that within five to ten years there may be enough data to give a certain analysis on whether or not dirty air has a significant impact on mental health.
He notes that the study found that there was a link between PM2.5 and depression across the world for different study designs – suggesting a significant relationship between the two.
The uncertainty surrounding the associations between mental health and pollution stem from the fact that the exact mechanisms of how it affects the brain are not clear at this point in time. There is evidence that tiny particulate matter can enter the blood and travel to the brain. Furthermore, air pollution is known to affect inflammation and stress hormones which are both associated with depression.
Another factor that clouds the results is the uncontrolled factors in the study such as the impacts of noise pollution and living near green spaces on study participants.
Braithwaite and her team did not find any associations of pollution with Bipolar disorder or Psychosis, and very limited evidence for anxiety.
Considering the fact that 1 in every 15 people in the UK attempt suicide, research on this subject is essential. A solution to high particulate matter will not only help mental health, but it will also help the environment.
Science and Technology Rowenna Hoskin