February 5, 2023

Air pollution can drive people to kill themselves

Air pollution can drive people to kill themselves
Air pollution can drive people to kill themselvesAir pollution can drive people to kill themselves

Pollution is bad for your health. That is well known. Polluted air increases the risk of strokes, heart disease and a list of respiratory illnesses that include asthma and lung cancer. High pollution levels are also linked to low productivity at work and poor scores on academic tests. But pollution may have a yet-more-sinister effect. It may also promote suicide.

Claudia Persico and David Marcotte of the American University, in Washington, DC, examined suicides throughout America between 2003 and 2010. They investigated the link between these and aerial levels of fine particulate matter known as PM2.5 because its particles are less than 2.5 microns across. These can enter the bloodstream via the lungs.

Suicide rates vary for many reasons, so the two researchers concentrated on correlating day-to-day changes in the number of suicides in particular places with fluctuating air-pollution levels caused by alterations in wind direction. In Boston for example, north-easterlies blowing into the city from industrial areas bring air carrying around five micrograms per cubic metre more PM2.5 than westerlies from upstate Massachusetts. The researchers worked out these wind-related pollution patterns for every county in America, and matched them with daily suicide statistics.

Their analysis, published as a working paper by the National Bureau of Economic Research, in Cambridge, Massachusetts, found that an increase of one microgram per cubic metre in PM2.5 in a given place was linked to an average rise in daily suicide rates of just under 0.5%, and if that increased level was sustained for a month, hospital admissions connected with attempted suicides rose by 50%.

An inflammatory conclusion

These results were robust even when controlling for factors like temperature and cloud cover, which could feasibly both have an effect on mood and be related to wind direction. There was, however, geographical variation. Dr Persico and Dr Marcotte found that the impact of pollution on suicide rates was greatest in poorer counties, in those with more unemployment, and in those with liberal gun-ownership laws, since access to a firearm presumably makes it easier for a potential suicide to turn thought into deed.

They suggest poor air quality worsens moods, which in turn increases the likelihood of someone experiencing suicidal thoughts. In a separate analysis they took data from surveys that asked people about their mood and mental state. They tested whether the answers were related to pollution levels in respondents’ home towns in the month leading up to the survey.

They found that a single additional day in a typical month during which PM2.5 levels were above 35 micrograms per cubic metre was associated with a small but consistent increase in how often people reported they felt depressed, had little pleasure in doing things or were tired and lacked energy. They also found an increase of around 1% in the number who had been told by a doctor that they had depression.

Previous research has found that pollution—and specifically the PM2.5 variety—can cause an inflammatory response in organs including the brain. Many researchers think inflammation may disrupt the normal operation of the brain’s reward pathways, which are important for regulating mood. Some trials have indeed found that anti-inflammatory drugs can improve mood in people with depression. And other studies have shown that people suffering from depression have consistently higher concentrations of proteins called cytokines, released during inflammation, in their blood—and that suicide victims, examined after death, have higher levels of inflammatory cytokines in their brains.

In America, average PM2.5 levels in populated areas are around twice the World Health Organisation recommended maximum of five micrograms per cubic metre. A study published in 2021 suggests meeting that figure might save 100,000 lives a year. In this context the 770 suicides which would, if Dr Persico and Dr Marcotte are correct, be avoided by this reduction are only a small extra saving. But suicide is such a tragic end to life that it would be a particularly welcome one.