The new horizons of planetary health

Planetary health is a powerful tool for widening the scope of assessments around health when looking at environmental stressors

Air pollution kills millions globally every year. Noise pollution in Europe causes more than 12,000 premature deaths and contributes to more than 48,000 cases of ischaemic heart disease annually. More than three billion people are highly vulnerable to the effects of climate change. Deforestation and loss of biodiversity increase the risk of spillover zoonotic infections in humans. All of these are environmental factors and stressors that have a direct effect on public health and have interlinked causes and solutions.

Framework

Planetary health is a framework that can be used to see the interlinkages between human health, animal health, and environmental health. While there are significant overlaps with ‘One Health’, which also aims to sustainably balance and optimise the health of people, animals and ecosystems, planetary health is often placed on a larger scale. It sees the quality, integrity, and health of the ecosystems around us, the biodiverse animal populations of the environment, and our place within these systems as dependent on each other and inextricably connected. This framework is now part of the World Health Organisation (WHO) approach to public health. It was included in the wording of the Budapest Declaration made by the WHO and United Nations Environment Programme last year.

In a paper in The Lancet in 2017, Dr Samuel Myers, Planetary Health Alliance, provided a visualisation of this framework. Dr Myers broke it down into five levels of interaction: Underlying drivers; ecological drivers; proximate causes; mediating factors; and the end health effects. Underlying drivers include factors such as technology and consumption. Under ecological drivers are environmental factors such as climate change, biodiversity loss, and environmental pollution. Proximate causes are the outcomes of these – air pollution, impact on food systems, and infectious health risks, to name a few. These factors are mediated by influences such as governance, culture, and behaviour. After all of that, we find health effects – infectious and non-communicable disease; injury; mental illness; and malnutrition. The health effects are by no means limited to these examples.

Planetary health is a powerful tool for widening the scope of assessments around health when looking at environmental stressors. Say, for example, we want to make a case for action on air pollution. Through a human health-centred approach, we may have to limit our advocacy to the links between exposure to polluted air and morbidity and mortality in humans. But when we widen our scope, we get a much clearer view of the fuller impacts, and the interconnections between them. In the case of clean air, we don’t just see the biomedical outcomes, we also see the effects on animal health, crop yields, the water cycle, and global warming. We can follow each one of these branches until we find a complex web of interrelations of planetary health factors.

We can also use the framework to look in the other direction – at an environmental or animal change – and see what they mean for human, animal, and environmental health.

Climate change is a big part of planetary health and using this framework can expand our expectations for a world with a hostile climate. We know that as the climate changes, weather extremes will become more severe, with hotter heatwaves, deeper droughts, and more severe storms. All of these are bad for health. But what about the effects on mental health of widespread deforestation? What about the effects on air pollution from dust storms? The effects of food security collapse with the loss of biodiversity and pollinators? The consequences for water and energy supply if glaciers no longer provide spring melt water? Planetary health provides us with multiple paths to chart, mitigate, and adapt to risk, but also to contribute to research and grow the evidence-base.

Research

Research is using this framework to examine the interlinkages. A 2022 study by Sudimac and colleagues found that an hour’s walk in the centre of Berlin, compared to an hour’s walk in the forest of Grunewald outside of Berlin, produced observable functional changes to the amygdala of participants on MRI, indicating an observable benefit of natural spaces on stress responses and brain function. A 2015 study by Taylor and colleagues looked at the density of trees in urban areas and antidepressant prescription rates. It found a decrease of 1.18 prescriptions per 1,000 population per unit increase in trees per kilometre of street.

A 2017 study by Ruokolainen and colleagues found that mucosal microbiomes, and prevalence of allergies and atopy, differed depending on the exposure of participants to diverse nature, with more exposure associated with less
allergic conditions.

Looking at more complex, multi-outcome relationships, research has shown that mycorrhizal mycelium fungi, existing in healthy soil and forests, can sequester up to 39 per cent of atmospheric carbon dioxide, and have been a historical driver of changes in climate.

A study in 2018 from Markandya and colleagues found that the cost of mitigating climate change would be paid for by the social savings from reducing air pollution associated with this mitigation. This is without even considering the parallel effects on water security, food security, biodiversity, noise pollution, desertification, and deforestation, which could be further explored through the planetary health lens.

Healthcare

What is healthcare doing with this new framework? Many researchers are building evidence by looking at these interlinkages. Studies across the EU and internationally are strengthening and communicating the benefits of action across multiple domains through the planetary health framework. Some are advocating for political action to ensure a future where the integrity of animal and environmental health is protected, through strong environmental protection and policy, and ensuring future planetary health. Some are pushing for sustainable, decarbonised health systems that signal to the rest of society that health is a critical issue when it comes to sustainability, especially as the health system globally is
responsible for about 5 per cent of
carbon emissions.

Healthcare professionals are also advising patients on an individual level, taking this research and policy change and intervening in the consultation to promote health. One such intervention is nature prescriptions, where selected patients are prescribed a period of exposure to nature, as they would be a medication. This is especially used for interventions related to mental health, blood pressure and cardiovascular conditions, respiratory conditions, and physical activity. A systematic review by Wen and colleagues found ‘forest bathing’ may significantly improve people’s physical and psychological health.

The planetary health framework, while primarily a tool for visualisation and analysis, underscores an
intuitive truth: Healthy environments lead to healthier people. Unhealthy, polluted, degraded, restricted environments make for unhealthy, unhappy people. It reminds us that we exist within natural environments upon which we depend for our health, and that individual and collective wellbeing cannot be separated from the health of the broader system.

Planetary health is a framework that can be
used to see the interlinkages between human health, animal health, and environmental health