Short-term spikes in pollution levels ‘linked to increased risk of suicide’

People exposed to higher levels of air pollution are more likely to suffer depression or take their own life, London researchers have found.

They raised concerns about the tiny PM10 and PM2.5 particulates that are emitted from the brakes and tyres of all types of vehicles — including “greener” electric buses and cars.

Experts worry that although central London’s ultra low emission zone is reducing nitrogen oxide exhaust gases, it is not cutting particulates because drivers are switching from petrol or diesel to hybrid cars to avoid paying the £12.50 daily levy.

Today’s study, led by University College London, is the first to use a “meta analysis” of five previously published studies to draw conclusions about the link between air pollution and mental health. 

World Health Organisation guidelines recommend that particulates — small airborne particles that include dust and soot — should be kept under 10µg/m3 (micrograms per metre cubed). Global city PM2.5 levels — the more dangerous smaller particles whose diameters are less than 2.5 micrometers — range from 114 and 97 in Delhi and Dhaka, to six in Ottawa and Wellington.

In UK cities, the average is 12.8µg/m3. The researchers estimate that lowering average air pollution levels to the WHO recommended limit could reduce urban UK residents’ depression risk by about 2.5 per cent.

Reducing average levels across the world from 44µg/m3 to 25µg/m3 could result in a 15 per cent reduction in depression, according to the research published in Environmental Health Perspectives

The number of UK suicides in 2018 increased by 686 on the previous year to 6,507, though the reasons for the deaths are unknown. 

Lead author Dr Isobel Braithwaite, from UCL Psychiatry and UCL Institute of Health Informatics, said: “We already know that air pollution is bad for people’s health, with numerous physical health risks ranging from heart and lung disease to stroke and a higher risk of dementia. Here, we’re showing that air pollution could be causing substantial harm to our mental health as well, making the case for cleaning up the air we breathe even more urgent.”

A 10µg/m3 long-term increase in exposure to PM2.5 particles increased the risk of depression by 10 per cent.

“We found quite consistent results across the studies we reviewed that analysed the relationship between long-term air pollution exposure and depression, even after adjustment for many other factors which could explain the association,” Dr Braithwaite said.

The researchers also found evidence of a connection between short-term changes in larger PM10 coarse particulates and the number of suicides, from pooling the results of four different studies. The risk of suicide appeared to be higher on days when PM10 levels had been high over a three-day period than after less polluted periods.

The researchers say they cannot yet confirm whether air pollution directly causes mental ill health, but say there is evidence to suggest possible causal mechanisms. “We know that the finest particulates from dirty air can reach the brain via both the bloodstream and the nose, and air pollution has been implicated in increased neuroinflammation, damage to nerve cells and to changes in stress hormone production, which have been linked to poor mental health,” Dr Braithwaite said.

For confidential support on mental health call the Samaritans on 116 123, email jo@samaritans.org or attend a local Samaritans branch.