A study links air pollution to an increased risk of suicide or suicidal thoughts

This is a methodologically sound systematic review and meta-analysis that provides relevant evidence on the association between certain air pollutants and suicidal behaviour. The study forms part of a growing body of literature showing that mental health cannot be understood solely in terms of individual or clinical variables, but also in terms of the environmental conditions in which everyday life takes place. Furthermore, the authors interpret the results cautiously and acknowledge significant limitations relating to methodological heterogeneity and the still small number of studies for certain exposures.

In my view, the study’s main contribution is not to demonstrate that pollution is a causal factor in suicidal behaviour, but to remind us that psychological distress always occurs within a specific context. Environmental pollutants may act through complex mechanisms, but they may also serve as indicators of environments that are more vulnerable from a social and living conditions perspective: neighbourhoods with poorer living conditions, lower environmental quality, greater daily stress or wider inequalities. These findings therefore encourage us to broaden our perspective on suicide prevention. Rather than seeking single explanations, they reinforce the need to understand how material, social and environmental conditions intertwine with the subjective experience of suffering and can increase the vulnerability of certain populations.

Firstly, I find this to be an interesting and timely study, as it broadens our understanding of the potential factors associated with suicidal behaviour. Suicidal behaviour is a multifactorial phenomenon and, as such, cannot be understood solely in terms of individual variables, but must also take into account social and contextual factors. In this regard, it is relevant to explore the potential role of environmental exposures such as pollution, in line with a growing body of literature on the influence of the environment on mental health.

Methodologically, the study is well-designed as a systematic review with a meta-analysis. One of its main limitations, acknowledged by the authors themselves, is the high heterogeneity of the included studies, which combine very different designs, use different methods to measure exposure to pollution, and do not always account in the same way for other factors that may influence the results—such as socio-economic status, which may be related to the environmental characteristics of the place where people live. Added to this is a wide geographical diversity, with a significant proportion of studies originating from Asia. All of this calls for caution when generalising the results to very different social, economic and political contexts.

Another important aspect is that, although the study appropriately distinguishes between suicidal ideation, suicide attempts and death by suicide, it subsequently analyses these outcomes together. These are related but not equivalent phenomena, and this decision limits the ability to determine whether the observed associations are similar for each type of suicidal behaviour.

Among the findings, although the study identifies associations with other pollutants, the most consistent evidence relates to air pollution and, in particular, to prolonged exposure to PM2.5 – extremely small particulate matter that can penetrate deep into the respiratory tract. This association remains when studies with a higher risk of bias are excluded, although it ceases to be significant when the different types of suicidal behaviour are analysed separately—an analysis for which, moreover, fewer studies are available. An association with nitrogen dioxide (NO₂), which is particularly linked to traffic and other combustion processes, is also initially observed, but this does not hold up when studies with a higher risk of bias are excluded.

Overall, the results provide evidence of an association between certain environmental exposures and suicidal behaviour, particularly in the case of prolonged exposure to PM2.5. However, the heterogeneity of the studies and the reduced consistency of some results in the more restrictive analyses call for caution. The findings are suggestive, but do not yet allow pollution to be considered an established risk factor or a causal relationship to be established. The study opens up an important line of inquiry that should be further explored to determine under what conditions, to what extent and for what types of suicidal behaviour these associations occur. If their relevance is confirmed, incorporating environmental factors into prevention could open up new avenues for action through public policy.

Without being able to view the supplementary material or read the methodology, it could be said that the authors have followed the protocol correctly to produce a high-quality systematic review.

This is a very important area of research, as it accounts for 1 per cent of mortality in Europe – that is, 10 deaths per 100,000 inhabitants – and in Spain, eight deaths per 100,000 inhabitants. Therefore, investigating which factors are linked to suicide-related mortality is essential for defining strategic prevention measures. There is already sufficient scientific evidence to suggest that air pollution, as an environmental factor, is linked to premature mortality and hospital admissions due to respiratory, cardiovascular and cerebrovascular problems, but there is growing evidence that it also affects mental health. In fact, this year we have published an article on mental health and air pollution in which we clearly see a link with anxiety and depression. The European Environment Agency has published results very similar to those in our article on its website, and they also discuss suicide.

The main limitation of this review is the small number of available studies and the high degree of heterogeneity amongst them (type of epidemiological study, type of study population, method of measuring the association, exposure-outcome relationship, etc.), which makes it difficult to obtain consistent results.

Given the results we have obtained and what we are finding in the scientific evidence regarding suicide and air pollution, it is clear that, in suicide prevention, environmental factors must be incorporated into public health policies, with particular attention paid to environmental and social inequalities.