The puzzling link between air pollution and suicide
Getty ImagesCould cleaner air reduce the risk of suicide? BBC Future looks at the evidence.
How do you prevent people from taking their own lives? There are no easy answers, but one thing is clear: suicide is a major public health problem. More than 700,000 people kill themselves worldwide every year, according to the World Health Organization (WHO).
Every year, on 10 September 2023, the WHO marks World Suicide Prevention Day, aiming to focus attention on the scale of the death toll and its causes.
People in the US might be particularly troubled to learn that the suicides there have increased by around 40% over the past two decades. Last year, almost 50,000 people in the US took their own life – one death every 11 minutes – and the nation now has one of the highest rates of wealthy, developed countries. (For comparison, the UK suicide rate is around 25% lower than that of the US).
Preventing these deaths is a complex problem, and there are no silver bullets. However, research in recent years has suggested that there are interventions that politicians and public health officials can make – and they extend beyond established responses like investing in mental healthcare provision, or reducing loneliness.
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For example, in 2018 researchers in the journal Science reported how Denmark had managed to reduce its suicide rate significantly by restricting access to the most dangerous means of suicide, as well as establishing specific Suicide Prevention Clinics for people with suicidal ideation.
Now a new frontier of potentially preventative research is emerging that might, at first, seem unrelated: improving air quality. Over the past few years, various studies have identified associations between raised levels of air pollution and suicide risk. What should we make of this evidence?
What does the research show?
In 2021, Seulkee Heo and colleagues at Yale University reviewed 18 studies that explored the association between air pollution and suicide. They found significant associations with increased suicide risk for particulate matter – the stuff emitted by wood burners, wildfires or construction dust – as well as the gases sulphur dioxide and nitrogen dioxide emitted by industrial facilities, fossil-fuel burning and some vehicles.
Getty ImagesThis chimes with a 2019 review of the research led by Isobel Braithwaite of University College, London. By analysing data from various studies, Braithwaite and colleagues found that, when particulate matter levels are high, the risk of suicide appears to be measurably higher over a three-day period. The review also ed the hypothesis that long-term air pollution exposure may increase the likelihood of depression.
A number of the studies have been conducted in Europe and Asia, but one recent analysis of US data, published by the National Bureau of Economic Research in Cambridge, Massachusetts, found that when particulate matter increased in US cities by one microgram per cubic metre daily suicide rates rose by up to 0.5%. (Unlike the other studies, however, this particular paper did not appear in a peer-reviewed journal.)
What might the biological mechanism be?
It's not known for certain, but researchers have their suspicions. Air pollution entering the lungs can inhibit the flow of oxygen into the bloodstream, and then the brain. Other studies unrelated to suicide have shown that this can lead to cognitive impairments, among other effects.
In the case of suicide risk, researchers suspect that pollution can lead to inflammation in the brain, deficits in serotonin, and disrupt stress response pathways, which can in turn make depressive behaviours and impulsivity more likely. It's possible, then, that bad air can affect how people think: leading to a brain fog that could encourage suicidal ideation without them realising.
What are the caveats to know?
The studies reviewed by the teams at Yale and UCL looked at associations – comparing statistics – rather than fully unpicking into the mechanisms and factors that could cause pollution to affect the brain.
As with any research that examines correlations, there could well be other environmental influences at play. For example, in their analysis Heo and colleagues also reviewed studies that found a correlation between suicide and high temperature, finding there is also a significant association between hot days and increased suicide rates. All else being equal, a 7C increase in temperature leads to a 9% higher suicide rate, explains co-author Michelle Bell of Yale. "A larger increase in heat would have a larger risk," she says.
While many of the studies investigating air pollution ed for the possible effects of hotter days, there will always be challenges when seeking to untangle the two, because they are closely related. Higher temperatures can lead to spikes in air pollution, write Heo and colleagues, and people may be more likely to breathe in air pollution on hot days because they open the windows.
Another area of uncertainty in the science is whether air pollution has different effects for suicidal ideation between men and women. (However, what we do know is that suicide disproportionately affects men. In the US, around 80% of suicides last year were male.)
Isn't air pollution already bad news for public health?
Breathing air pollution is bad for us in many other ways – that science is well-established.
This week was also marked by International Day of Clean Air for Blue Skies, on 7 September, led by the United Nations. Its organisers highlight the health risks of air pollution, emphasising that "tiny, invisible particles of pollution penetrate deep into our lungs, bloodstream and bodies…and are responsible for about one-third of deaths from stroke, chronic respiratory disease, and lung cancer, as well as one quarter of deaths from heart attack."
So, how could this new knowledge help us prevent suicide?
Past experience, from the likes of Denmark and elsewhere, shows that successfully reducing suicide rates requires multiple interventions, at a local and national scale. Air pollution increases the likelihood of suicide by a few percentage points, but eliminating it won't solve the problem.
However, if the link with suicide is confirmed and elaborated by more research, it would provide all the more reason for public warnings and awareness campaigns when bad air is elevated, say Heo and colleagues. With climate change, they warn, desertification, droughts and wildfires become more likely, all of which are known to increase air pollution. These problems will be bad enough, and if we factor in the additional risk of people killing themselves too, then tackling them will require extra urgency.
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If you or anyone you know is affected by this story, here are some resources that can help.
The International Association for Suicide Prevention has a list of global agencies that may also be able to provide immediate .
In the UK and Ireland:
The Samaritans are open 24 hours a day. Call 116 123 or email [email protected]
The Campaign Against Living Miserably (Calm) offers to men. Call 0800 58 58 58 between 17:00 and 00:00 every day or visit their webchat page here.
In the US:
If you are in crisis, please call the National Suicide Prevention Lifeline at 1-800-273-TALK (8255) or the Crisis Text Line by texting TALK to 741741.
In Australia:
Call Lifeline on 13 11 14 or chat online, nightly seven days a week.
In Canada:
If you are in crisis, call 1-833-456-4566 (4357) or text 45645. For more information about suicide prevention, visit Centre for suicide prevention.
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