Air pollution is already known to affect the lungs, heart and blood vessels. New research suggests its impact could extend further, with polluted air also associated with a higher risk of suicide, suicide attempts and suicidal thoughts.
An international research team led by scientists at Queen’s University Belfast reviewed evidence from studies examining the relationship between environmental pollution and suicide-related outcomes. The findings, published in the Journal of Epidemiology and Community Health, identified the strongest associations with fine particulate matter and nitrogen dioxide.
Researchers said the findings add to growing evidence that environmental conditions may play a role in mental health. They also suggested that air pollution could be considered a potentially modifiable environmental risk factor within broader suicide prevention strategies.
The study does not mean that polluted air directly causes suicidal thoughts or behaviour. Experts stressed that suicide has multiple causes and that factors such as mental health conditions, social circumstances, economic difficulties, physical health, housing and living conditions can all influence risk.
The research team examined studies published between January 2010 and April 2024. Of 287 studies considered for detailed assessment, 45 met the criteria for inclusion in the systematic review.
Most of the available research focused on air pollution. Thirty-eight studies examined air pollution, while smaller numbers looked at water, noise and light pollution.
Data from 29 studies were suitable for a pooled analysis. The analysis found statistically significant associations between short-term exposure to PM2.5 and PM10 and suicide-related outcomes. Long-term exposure to PM2.5 and nitrogen dioxide was also associated with death by suicide, suicide attempts and suicidal thoughts.
PM2.5 refers to very fine particles measuring 2.5 micrometres or less in diameter. Because these particles are so small, they can travel deep into the respiratory system. They are produced by sources including vehicle traffic, industrial activity and the burning of fossil fuels.
PM10 particles are larger but can still enter the respiratory tract. Nitrogen dioxide, or NO2, is another major air pollutant commonly associated with vehicle exhaust and combustion.
The findings suggest that exposure does not necessarily need to be prolonged to show an association. Both short-term and long-term exposure appeared relevant for different pollutants and outcomes.
The researchers also examined whether other environmental pollutants could be linked to suicide risk.
A separate review of 16 studies suggested possible associations involving sulphur dioxide, ozone and noise pollution. However, the evidence was less extensive than that available for particulate matter and nitrogen dioxide.
The researchers could not conduct a pooled analysis of water and light pollution because there were too few studies and the methods used to measure outcomes varied significantly. Evidence relating to those forms of pollution was therefore considered inconclusive.
Scientists are still investigating the biological mechanisms that might explain the relationship between air pollution and mental health.
Previous research has linked pollutants such as PM2.5, PM10 and nitrogen dioxide with inflammation and effects on the nervous system. Researchers said these processes could potentially influence brain function, mood and the body’s ability to cope with stress.
There may also be indirect effects. Traffic and environmental pollution are often accompanied by noise, congestion and disruption to daily routines. Persistent noise and other environmental disturbances can affect sleep and disrupt the body’s natural circadian rhythm.
Poor sleep, chronic stress and other effects of living in heavily polluted environments could, in turn, influence mental wellbeing.
These are possible pathways rather than established explanations for the findings. More research is needed to determine whether pollution itself is responsible for the observed associations.
Health experts have also warned against interpreting the findings as proof that air pollution causes suicide.
Areas with high levels of air pollution can differ from cleaner areas in many other ways. They may have higher levels of socioeconomic deprivation, greater population density, different housing conditions and more traffic. Physical health problems can also be more common in some highly polluted communities.
These factors make it difficult for researchers to determine whether pollution itself is responsible for an increased suicide risk.
Experts therefore say the findings should not be used to predict suicide risk for an individual person. Reducing air pollution should also not be viewed as a standalone suicide prevention measure.
Suicide remains a major global public health concern, with more than 720,000 people estimated to die by suicide worldwide each year, according to the World Health Organization.
The new research adds another dimension to the growing scientific discussion around the health effects of polluted air. While the findings do not establish a direct cause, they suggest that environmental conditions may be worth considering alongside the psychological, social and biological factors already known to influence mental health.
Researchers say larger and better-designed studies will be needed to understand the connection more clearly. The findings could eventually help public health experts examine air quality as part of wider strategies aimed at protecting both physical and mental wellbeing.
