In a new study, researchers found that people exposed to higher levels of air pollution are more likely to experience depression or die by suicide.
This is the first systematic review and meta-analysis of evidence connecting air pollution and a range of mental health problems.
The research was led by a team at University College London.
The team reviewed the study data from 16 countries.
They found that, if the link with depression reported in some of these studies is causal, then reducing global average exposure to fine particulate matter (PM2.5) air pollution from 44 micrograms per meter cubed (μg/m3) to 25μg/m3 could result in a 15% reduction in depression risk worldwide.
The World Health Organization guidelines recommend that fine particulate matter pollution—small airborne particles that can include dust and soot—should be kept under 10μg/m3.
Previous research has shown 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.
The current study shows 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 team says they found quite consistent results across the studies they reviewed that analyses the link between long-term air pollution exposure and depression.
The association seems to be similar in magnitude to those that have been found for some physical health impacts of particulate matter, such as all-cause mortality.
Global city PM2.5 levels range from 114 and 97 in Delhi and Dhaka, to 6 in Ottawa and Wellington.
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 appears to be measurably higher on days when PM10 levels have 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.
The lead author of the study is Dr. Isobel Braithwaite (UCL Psychiatry and UCL Institute of Health Informatics).
The study is published in Environmental Health Perspectives.
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