Biodiversity and human health

Published on December 5th, 2024

As the recent repeated climate-related tragedies in several countries (hurricanes Helene and Milton, flood in Valencia) demonstrate, we are now observing what was predicted many years ago on the basis of scientific models. As William Ripple and colleagues, among others, have stressed,  “We are on the brink of an irreversible climate disaster. This is a global emergency beyond any doubt. Much of the very fabric of life on Earth is imperiled. We are stepping into a critical and unpredictable new phase of the climate crisis. (…) For half a century, global warming has been correctly predicted even before it was observed—and not only by independent academic scientists but also by fossil fuel companies. (…) Despite six IPCC reports, 28 COP meetings, hundreds of other reports, and tens of thousands of scientific papers, the world has made only very minor headway on climate change, in part because of stiff resistance from those benefiting financially from the current fossil-fuel based system” (1). Others have introduced the term of “polycrisis” to describe the occurrence and interaction of multiple threats to the planet (2). Though the effects of climate change are now easily visible, we may be underestimating other key aspects of the polycrisis. Primary prevention has failed for climate change so far, and might fail also for other components of the planetary boundaries, namely the loss of biodiversity. Here I will particularly focus on the impacts of biodiversity loss on health.  

We now know a great deal about climate change and its effects on the planet and our health. In contrast, the impacts of biodiversity loss have only recently begun to be studied from a scientific perspective, and still very little from a social and economic perspective. It is to be hoped that the culpable delay in nations reacting to climate change will not be matched by an equal delay in curbing biodiversity loss, a phenomenon at least as important. There are two major limitations in our knowledge of the problem: what is the extent of biodiversity loss, and how does this loss fit into the larger process of erosion of natural capital. Regarding the first aspect, the figure of 70 percent reduction in biodiversity since 1970 is often cited, but this figure is based on vertebrates alone and on a limited number of counts (just over 5,000 species). Others consider not so much extinctions (the last stage), but the various stages at which different species are placed, which include categories such as “partially threatened, vulnerable, endangered, critically endangered, and extinct.”  The British Royal Society calculates that the extinction rate of mammals today is more than 1,000 times higher than in the pre-human period (inferred from fossils)(3). What matters is that the species descending in the ladder, that is those moving down to a category of greater severity, are far more numerous than the ascending ones (and the apparently increasing speed of the transition from one stage to the next also counts, of course). What is more, we do not even know how many species there are: the recent Tara Oceans marine expedition, which was extraordinary for its discovery of so many as yet unknown natural phenomena, identified millions of new genes corresponding to hundreds of thousands of new species (and 5,500 new RNA viruses).  

The second still obscure aspect is the extent of HANPP (Human Appropriation of Net Primary Production). Net primary production (NPP) is the amount of biomass produced per unit of land area and time. It is basically a measure of how much natural capital is able to reproduce itself from Sun-fueled chlorophyll photosynthesis.  NPP is the source of all so-called ecosystem services, that is, the goods that nature makes available to species including ours: oxygen, food, water, medicines, tissues, etc. The best estimate for NPP loss (appropriated by humans) seems to be 24 percent of the annual primary productivity. In short, the magnitude of natural resource extraction by our species is about 24 percent (with a constant increase in the last decades, and much higher in Asia). Animal species and therefore biodiversity strictly depend on NPP. The consideration is whether nature is able to replace what we extract, and here the problem is not only quantitative. In fact, the loss of biodiversity is very different depending on whether it affects crucial species at the crossroads of interactions with other species, in terms of nutrition and ecological equilibrium. The loss of one species can give rise to a chain of catastrophic events for the species that depend on it (think of pollinators). Many species are niche builders, such as beavers (and, on a planetary scale, the human species), that is, they modify the environment in ways that increase the likelihood of survival for themselves while increasing or decreasing it for other species. 

The consequences for us humans of biodiversity loss fit into this context, and they too are largely circumstantial for the moment. A first aspect is migrations, not only of humans but of many other species. The Royal Society has drawn attention to the fact that the impact of environmental changes, including climate change, leads to selection of less specialized, more resilient and opportunistic species (typically bats), with an overall decrease in natural capital and a kind of biological entropy.  In addition, environmental changes have induced animal species of tropical forests to mass migration. According to a major article in 2022, the likelihood that due to the abandonment of their habitats, species that have never met will have to coexist in a new habitat will increase 4000-fold in the coming years (4). One consequence of these migrations is the increased likelihood of spillovers, including the transmission of new viruses to the human species. Therefore, one of the main preparedness interventions against pandemics is the establishment of animal migration monitoring activities, along with periodic sampling of infectious agents in wild and domestic species, and in water samples in high-risk countries.  

Regarding human migration related to the climate crisis and , according to the Internal Displacement Monitoring Center, in 2021 climate change and environmental crises generated 24 million internally displaced persons (i.e., within the country of residence), a huge number considering that UNHCR counted 89.3 million forced migrants worldwide in the same year. By 2050, climate change is expected to displace 200-250 million people, or about 3 percent of the population of sub-Saharan Africa, South Asia, and Latin America.  One in 45 people in the world could be climate-induced migrants in the future.The pace of migration can be gradual, when it is generated by slow processes such as sea level rise, salinization of agricultural land, desertification, drought, famine, and increasing water scarcity; or sudden, during and after life-threatening climate events such as floods, cyclones, and storms. 

Another phenomenon related to the loss of biodiversity, broadly understood, is the progressive simplification of the microbiome in our species. The most biodiverse human microbiome is certainly that of hunter-gatherers, especially Africans, such as the Hadza tribes in Tanzania and those who speak the Khoi-San languages in southern Africa. Their microbiome is “as diverse as a jungle” and even shows seasonal fluctuations that adapt well to changes in diet throughout the year (5). Our microbiome is not even partially overlapping with that of hunter-gatherer populations, as a consequence not only of diet but also of urban lifestyle with little contact with land, plants and microbes.  The spread of asthma but also of various diseases of immune or auto-immune origin is attributed to the simplification of the microbiome. 

Finally there is the problem of nutritional health. It appears from various pieces of research that our diet has undergone a progressive process of simplification, in recent years partly due to the spread of ultra-processed foods. By simplification is meant a reduction in the number of species entering the daily diet, a phenomenon that goes hand in hand with the spread of monocultures in the case of vegetables: fewer species produced and fewer species ingested. In terms of health, it has been shown repeatedly that populations in low-income countries that have a diet based on a few species also have dietary deficiencies and achieve “nutritional adequacy” with more difficulty. Planetary edible foods provide at least 26,000 different biochemical compounds, but  many of the properties and functions in the physiological balance of animal species are unknown.  Linked to this is the recent observation (by the EPIC research coordinated by Imperial College and the WHO International Agency for Research on Cancer) that fewer species consumed in the diet correspond to increased early mortality and also increased risk of digestive tract cancers (6, 7).These are still largely unexplored phenomena that shed new light in such a complex area of research as the relationship between nutrition and chronic diseases. Taking this complexity into account, next to the traditional nutritional approach based essentially on single molecules (vitamins, micronutrients, essential elements, etc.) and corresponding supplements, a more “systemic” strand is emerging, based for example on Anthony Fardet's three Vs (Vrai, Varié, Végetale: true, varied, vegetable)(8). 

A question emerges at this point, namely whether the watchword of “sustainability” is sufficient. If it is true that we are consuming 24% of natural capital, then we should also put the planet in a position to regenerate it if we do not want to lose ecosystem services catastrophically (on this see ref 9). 

In conclusion, we have to admit that so far the primary prevention of the multiple consequences of climate change, including health effects, has failed, and the polycrisis concerning the progressive erosion of the natural capital and its related ecosystem services poses additional challenges. 

Recommendations 

Some policy recommendations that stem from the analysis above can be put forward in a provisional way, for further discussion. At the local level, policy-makers need to be sensitized. While recent events like the flood in Valencia or the Milton and Helene hurricanes have increased the level of awareness towards climate change, loss of biodiversity is largely ignored by broad segments of the population and local policy-makers. Cement is still the common solution even to address adaptation to the consequences of climate change, like floods. Locally, planning the extension of agricultural land does not usually take into account shrinking of forests and wilderness, if this is not enforced by national or international laws. At the international level, several initiatives have been taken in this direction, such as the Kunming-Montreal Global Biodiversity Framework, adopted during the Conference of Parties (COP) 15 in 2022 (10). It aims to protect at least 30% of the world’s land and water areas that are important for biodiversity by 2030. Within the Biodiversity Strategy framework, the European Council recently adopted the Nature Restoration Law (11), despite strong opposition from the agricultural sector. The fact is that preservation of biodiversity cannot be limited to the creation of protected zones but it must also entail changes in agricultural practices, that allow the protection and regeneration (9) of plant and animal species. Of course this avenue is far from being straightforward to follow, partly because of objective reasons and not only for political resistance. For example, the European legislation also aims to reduce considerably the use of pesticides and promote organic farming, but this is in contrast with productivity of agriculture. A decline in productivity means an extension of farmland at the expenses of forests and biodiversity, to maintain the same amount of food produced. This type of conflicts is currently not thouroughly discussed in the political arena, and proposed solutions lack clear scientific evidence.  

One way to increase the interest towards preservation of biodiversity is to stress the health co-benefits. For example, in 2020 the World Health Organization (WHO) published its Guidance on mainstreaming biodiversity for nutrition and health (12) , which emphasised the importance of maintaining agrobiodiversity in ensuring access to a nutritious and healthy diet.  Like for climate change, stressing the health benefits of mitigation of the loss of natural capital can be instrumental to persuade citizens and policy-makers. 

Of course, along with legislative initiatives, also actions by individuals count if there is a general climate of commitment and shared goals. These are some of the individual behaviors that can contribute substantially to both mitigating climate change and preserving biodiversity: 

- Reduce meat consumption – much of land use is devoted to animal farms for meat production, or is used for pasture 

- Reduce unnecessary consumption and the production of waste – pollution is an important cause of loss of animal and vegetable species  

- Respect green spaces and protect them. 

Changes in individual behaviors make sense in a context of active political engagement. In a positive political climate of ecological transition and industrial and agricultural reconversion, individual behaviors will also be encouraged and promoted. 

Ripple W J et al The 2024 state of the climate report: Perilous times on planet Earth. BioScience  biae087, 2024.  https://doi.org/10.1093/biosci/biae087 

Jørgensen P et al. Evolution of the polycrisis: Anthropocene traps that challenge global sustainability. Phil. Trans. R. Soc. 2023; B 379: 20220261. https://doi.org/10.1098/rstb.2022.0261 

Johson C N. Past and future decline and extinction of species. The Royal Society,  https://royalsociety.org/news-resources/projects/biodiversity/decline-and-extinction/ 

Carlson C J et al, Climate change increases cross-species viral transmission risk. Nature. 2022; 607, pages555–562  https://www.nature.com/articles/s41586-022-04788-w 

Dominguez Bello et al, Preserving microbial diversity. Science 2018; 362(6410):33-34.2018 https://pubmed.ncbi.nlm.nih.gov/30287652/ 

Hanley-Cook et al, Food biodiversity and total and cause-specific mortality in 9 European countries: An analysis of a prospective cohort study. PLOS Medicine 2021; 18(10): e1003834. https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1003834;  

Huybrechts et al, Food biodiversity and gastrointestinal cancer risk in nine European countries: Analysis within a prospective cohort study. European Journal of Cancer 2024; 210: 114258 https://www.sciencedirect.com/science/article/pii/S0959804924009146 

Fardet A, Rock E. Chronic diseases are first associated with the degradation and artificialization of food matrices rather than with food composition: calorie quality matters more than calorie quantity. Eur J Nutr 2022 Aug;61(5):2239-2253 https://pubmed.ncbi.nlm.nih.gov/35067754/ 

Illy A, Vineis P. No sustainability without regeneration.  Anthropocene Science 2024. https://doi.org/10.1007/s44177-024-00080-w 

Conference of the Parties to the Convention of Biological Diversity. Kunming-Montreal Global Biodiversity Framework. (2022). 

European Commission. Nature Restoration Law. (2024). https://environment.ec.europa.eu/topics/nature-and-biodiversity/nature-restoration-law_en 

World Health Organization. Guidance on mainstreaming biodiversity for nutrition and health. (2020). https://www.who.int/publications/i/item/guidance-mainstreaming-biodiversity-for-nutrition-and-health 

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