A view of Thames river and London at sunset with red sky and air pollution with Tower bridge

Air pollution linked to increased risk of depression and suicide

Image credit: Osnuya - Dreamstime

People exposed to high levels of air pollution have higher rates of depression and suicide, a new analysis of global data has found.

While the effects on the body from breathing polluted air – such as asthma or heart disease – are well-established, the data reviewed by researchers from University College London (UCL) suggests that pollution may also affect a person’s mental health.

As part of the study, Dr Isobel Braithwaite of UCL Psychiatry and UCL Institute of Health Informatics and her colleagues assessed 25 studies published up to late 2017, for a meta-analysis on the links between emissions and mental health.

The team found that an individual living for at least six months in an area with twice the World Health Organisation’s (WHO) recommended limit for fine particulate matter, aka PM2.5, would have a 10 per cent increased risk of developing depression compared to a person living in an area that met the limit.

The findings, published in Environmental Health Perspectives, also show evidence of an association between short-term changes in PM10 exposure and the number of suicides.

The scientists said the risk of suicide appeared to be “measurably higher” on days when PM10 levels were high over a three-day period, with figures showing a 2 per cent increase in suicide risk for every 10 micrograms per cubic metre (μg/m3) rise in the average pollution level.

The WHO’s guidelines recommend that PM2.5 should be kept under 10μg/m3 on average over a year. People living in major UK cities are exposed to an average of 12.8μg/m3 of average particulate matter per annum, while Londoners may experience 13.3μg/m3 annually.

“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 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 estimate that lowering average air pollution levels to the WHO recommended limit could reduce the risk of depression among those living in the cities by roughly 2.5 per cent.

Braithwaite argued that establishing the links between pollution and mental health plays a vital role in the reduction of air pollution. She noted, however, that the UK has not yet adopted the WHO guidelines on PM2.5, despite London mayor Sadiq Khan saying he was committed to doing so.

“Knowing it 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 adds to the weight of the argument for cleaner air and policies that achieve it,” Braithwaite said.

However, the researchers said they cannot yet confirm whether air pollution directly causes mental ill health, but explained there are “a number of biologically plausible mechanisms that may underlie such a link”.

Dr Braithwaite said: “These [mechanisms] include the fact that exposure to air pollution increases the levels of inflammation within the brain, which has been linked with depression and other mental health problems through impacts on brain development and, potentially, through impacts on stress hormone production.

“We also can’t rule out the possibility that some or all of the relationship we observed is actually due to factors associated with both local air pollution levels and depression risk, but which were not fully accounted for by the individual studies, such as noise pollution or access to green space.”

In October, new figures from the European Environment Agency (EEA) found there were around 400,000 premature deaths in Europe in 2016 as a result of air pollution.

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