People who are exposed to higher levels of air pollution are more likely to experience depression or die by suicide, researchers have discovered.
The study of data from 16 countries, led by University College London (UCL), suggested that reducing global average exposure to fine particulate matter (PM2.5) air pollution from 44 micrograms per metre cubed (µg/m3) to 25µg/m3 could result in a 15% reduction in depression risk worldwide.
The World Health Organisation guidelines recommend that fine particulate matter pollution – small airborne particles that can include dust and soot – should be kept under 10µg/m3.
“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,” said the study’s lead author, Dr Isobel Braithwaite. “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.”
The researchers also found that a 10µg/m3 increase in the average level of fine particulate matter people were exposed to over long periods was associated with an approximately 10% increase in their odds of depression.
In UK cities, the average particulate matter level that people are exposed to is 12.8µg/m3. The researchers estimated that lowering average air pollution levels to the WHO recommended limit of 10µg/m3 could reduce urban UK residents’ depression risk by roughly 2.5%.
The researchers also found evidence of a connection between short-term changes in coarse particulate air pollution (PM10) exposure and the number of suicides. The risk of suicide appeared to be measurably higher on days when PM10 levels were high over a three-day period than after less polluted periods.
The researchers said they cannot yet confirm whether air pollution directly causes mental ill-health, but said 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,” Braithwaite said.