Climate and brain health

When we think of mental health, we tend to think only of the effect of changed climate and weather on psychiatric disorders. Events such as fires, floods and storms can cause deep psychological trauma. Longer-term changes, such as drought and desertification, crop failure and famine, can lead to social displacement and societal violence, which will have an impact on rates of psychiatric disorder.^{Reference Palinkas and Wong5} But the more immediate and graver threat is posed, once again, by the key driver of climate collapse: air pollution.

Studying the link between exposure to air pollution and the risk of acute psychiatric disorder is complex because those most exposed to pollution are the most disadvantaged members of society, who are also least likely to be diagnosed and treated^{Reference Braithwaite, Zhang, Kirkbride, Osborn and Hayes6} – yet another reason, we note, for placing poverty and social inequality firmly at the centre of the psychiatric agenda.^{Reference Byrne and James7} Nonetheless, a recent systematic review concludes that ‘extant literature suggests that air pollution is associated with increased depressive and anxiety symptoms and behaviors, and alterations in brain regions implicated in risk of psychopathology’.^{Reference Zundel, Ryan, Brokamp, Heeter, Huang and Strawn8} Short-term exposure to airborne particulate matter containing particles <2.5 μm in diameter (PM_2.5) is associated with increased emergency department visits for psychiatric emergencies,^{Reference Kim, Shin, Song, Ro, Kong and Kim9} and even short-term exposure to air pollution has adverse effects on cognitive performance that a Nature Aging editorial review described as ‘quite startling’.^{Reference Ryan and Owen10} Long-term exposure, predictably, is associated with increased incidence of schizophrenia spectrum disorder, depression and anxiety disorders.^{Reference Nobile, Forastiere, Michelozzi, Forastiere and Stafoggia11} Added to this, the increase in heatwaves and extreme heat have implications for cognitive performance affecting areas such as education, industry and administration.^{Reference Zhu, Hu and Yu12}

The evidence of the impact of air pollution on brain structure and function suggests that risk of neurodegenerative disease may also be increased. And, unsurprisingly, there are robust links between air pollution and cognitive decline and dementia^{Reference Peters, Mudway, Booth, Peters and Anstey13,Reference Shi, Zhu, Wang, Hao, Zhang and Schwartz14} and Parkinson's disease.^{Reference Murata, Barnhill and Bronstein15} Although the mechanism is not clear, it is likely that the same pathway is involved as in cardiovascular disease and stroke: a pro-inflammatory effect.^{Reference Jankowska-Kieltyka, Roman and Nalepa16–Reference Cory-Slechta, Merrill and Sobolewski18}

Although the links between air pollution and neurodegenerative disease are of concern, the most disturbing finding is the association with neurodevelopment. Exposures in utero to fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂) are associated with deficits in cognitive and psychomotor development in children. These effects are evident as early as 15 months,^{Reference Lertxundi, Baccini, Lertxundi, Fano, Aranbarri and Martínez19,Reference Li, Liao, Hu, Bao, Mahai and Cao20} and are evident across a wide range of real-life indices of cognitive performance.^{Reference Gartland, Aljofi, Dienes, Munford, Theakston and van Tongeren21–Reference Morgan, Bailey, Trifonova, Naik, Patterson and Lurmann25} Air pollution in utero and subsequently is also linked with risk of autism spectrum disorder^{Reference Dutheil, Comptour, Morlon, Mermillod, Pereira and Baker26,Reference Yu, Rahman, Carter, Lin, Zhuang and Chow27} and attention-deficit hyperactivity disorder.^{Reference Thygesen, Holst, Hansen, Geels, Kalkbrenner and Schendel28}

A disturbing aspect of these associations is that they indicate that widespread and pervasive effects on neurodevelopment are already affecting children around the world. We do not yet know the long-term implications of these effects for mental health and risk of psychiatric and neurodegenerative disease in later life, but frankly, based on the observed effects so far, the outlook appears grim. This concern is echoed by the recent reports of the European Environmental Agency, which has just issued a report detailing the impact of air pollution on children.²⁹

Nor is air pollution the only way in which the fossil fuel industry is adversely affecting both climate and health. The noise generated by air, road and rail transport has an impact on both cardiovascular^{Reference Münzel, Sørensen and Daiber30} and mental health.^{Reference Lan, Roberts, Kwan and Helbich31} And, more ominously, it is linked to cognitive impairment in middle-aged adults and to poorer school attainment in children.^{Reference Thompson, Smith, Bou Karim, Shen, Drummond and Teng32} Research into transport noise exposure is far from complete, so the current literature may well underestimate the scope and significance of its effects. The same applies to microparticle pollution associated with wear of vehicle tyres (tyres are, we remind the reader, another product of the petrochemical industry). Although it is clear that tyres are an important source of inhaled pollutants,^{Reference Kim, Park, Moon, Son, Hong and Wi33} further research is needed to clarify the independent contribution of these pollutants to the global burden of disease caused by air pollution.

A challenge to traditional boundaries

It is clear from the associations presented above that the distinction between psychiatric disorder, impaired neurodevelopment and neurodegenerative disorders is unhelpful when tackling the impacts of the climate crisis on health and quality of life. All of these disorders are significantly associated with exposure to the key driver of climate collapse – air pollution. They are occurring in the same brains of the same people, and are strongly correlated. For this reason, IDE has reconfigured the working group on climate and mental health to focus on climate and brain health.

This broadening of scope has several advantages. The first is that it switches the focus from the classification of medical disorders rooted in a mind/body dichotomy to a focus on the health of the person. The brain and its function in the context of the whole person as a member of society is the paradigm that provides a unifying framework. Second, mental disorder is a stigmatising term, which many people would be reluctant to apply to themselves. However, everyone has a brain and most people are rightly concerned about their risk of neurodegenerative disorder in later life. So the focus on brain health allows the climate message to reach a broader audience. Critically, many of us have children whom we cherish more than we do ourselves. The realisation that exposure to air pollution begins damaging the brain even before your child is born is one that no parent can accept – the present authors included!

The change of perspective from mental health to brain health also exposes one of the weaknesses of the health professions in mounting an appropriate response to the climate crisis. The compartmentalisation resulting from medical specialism means that there is no professional body to advocate for brain health. We in IDE believe that there should be no need for such an environmental organisation of health professionals. Our professional bodies should advocate for the health of the population as part of their societal role. However, even if the various bodies were to embrace this role wholeheartedly, there would still be the problem of transdisciplinary cooperation. The distinctions between health specialties that have their roots in the past are not fit for purpose in the current crisis.

The climate crisis is a brain health disaster that threatens all of us and – most worryingly – threatens the future of our children. The situation demands urgent coordinated action by healthcare professionals and organisations.^{Reference Bailey, Poole and James34} The Royal College of Psychiatrists has already declared a climate and ecological emergency that is having an impact on the mental health of populations, including the amplification of existing inequalities.³⁵ And, writing in this journal, Romeu has proposed that psychiatrists have a moral responsibility to take action.^{Reference Romeu36} The bold step of placing this action in the wider context of brain health will promote a coherent and holistic vision of the problem and better able us to take concerted action to tackle it.

All health professions urgently need to mount a widespread response to this crisis that is coherent and transdisciplinary. And such a transdisciplinary framework stands to benefit quality of care and coherence of research and teaching. What are we waiting for?