The RCPsych Article of the Month for August is from The British Journal of Psychiatry (BJPsych) and is entitled ‘Association between particulate matter air pollution and risk of depression and suicide: systematic review and meta-analysis’ by Xuelin Gu, Qisijing Liu, Furong Deng, Xueqin Wang, Hualiang Lin, Xinbiao Guo and Shaowei Wu.

Depression, as one of major mental disorders, is highly prevalent in the population and is closely associated with suicide outcome. Both of these two mental disorders have been identified as essential contributors to global disease burden. In 2016, depressive disorder accounted for about 44 million disability-adjusted life-years (DALYs) and 34.1 million years lived with disability. In 2015, suicide was the second leading cause of death among those aged 15-29 years. The prevalence of depression and suicide has been increasing rapidly and effective treatments for depression are not easily accessible, and therefore much attention should be paid to the prevention of depression and suicide. However, knowledge on the preventable environmental risk factors of these mental disorders are still lacking, especially in low- and middle- income countries.

Ambient particulate matter (PM) pollution – one of the most important environmental risk factors for human health – was responsible for 105.7 million DALYs globally in 2016, ranking sixth among behavioural, environmental and occupational, and metabolic risk factors. It was also among the top ten risk factors for attributable deaths in 195 countries and territories, including India and China, where it ranked the third and fourth place in 2016, respectively.

Some recent studies examined the effect of ambient PM pollution on depression and suicide with inconsistent conclusions. In this meta-analysis, we identified 14 relevant articles (7 for depression and 7 for suicide) published before 13 March 2018, with data from 684 859 participants. We found that exposure to ambient PM2.5 was associated with increased depression risk in the general population while the association between PM2.5 and suicide was marginally significant. Moreover, we did not observe any significant associations between exposure to PM10 and depression/suicide. These findings were robust in sensitivity and subgroup analyses.

Although the exact mechanism has yet to be clarified, one hypothesis is that mental disorders occur because of oxidative stress and neuroinflammation pathways being induced by PM2.5. Moreover, PM2.5 appeared to have a stronger association with depression in a relative long-term lag pattern, suggesting a potential cumulative effect over time.

Because of the ubiquitous existence of PM2.5 pollution and the increasing prevalence of depression and suicide, the associated disease burden of mental health would be substantial at the population level. Therefore, targeted strategies such as more stringent air pollution standards, air quality control measures and individual protection behaviours may be helpful to prevent the onset and exacerbation of depression or to decrease suicide cases due to air pollution, especially in heavily polluted regions and high-risk population.

Complimentary access has been provided to this article for a limited time.

RCPsych Article of the Month
Each month a paper is selected by one of the Editors of the five RCPsych Journals (The British Journal of Psychiatry (BJPsych), BJPsych Open, BJPsych Advances, BJPsych Bulletin and BJPsych International) View the full collection here.

Why I chose this article:

“Several papers in BJPsych this month consider the potential effect of neighbourhood-level environmental factors on depression and associated outcomes. Gu et al move into the atmosphere to consider the relationship between particulate matter air pollution and risk of both depression and suicide. Following a systematic review and meta-analysis, the authors conclude that increased ambient PM2.5 (particles with diameter 2.5 μm or less) concentration is strongly associated with increased depression risk in the general population, with evidence to support the possibility of a cumulative exposure effect over time. A marginally significant positive association with risk of suicide was also identified in this study but no associations were found between concentration of PM10 and either of the outcomes of interest. The authors note that the mechanisms underlying the associations found remain unclear and call for further research, including to examine the impact of lowering pollution levels.”

Professor Kimberlie Dean, BJPsych Highlights Editor

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