Biodiversity – our health depends on it

The consequences of biodiversity loss have implications not just for the environment but also for human health, particularly in the prevalence of allergies and chronic inflammatory diseases such as eczema and asthma.

That is the conclusion from a recent study by Professor Ilkka Hanski and his colleagues from the Metapopulation Research Group based in the Department of Biosciences at the University of Helsinki, published in the Proceedings of the National Academy of Sciences earlier this year.

In their study of Finnish adolescents, the researchers showed that those who had reduced contact with the natural environment, both forest and agricultural land, were more likely to be affected by allergic conditions and had less diverse bacteria on their skin.

As Hanski explains, the association between allergic disposition and biodiversity was demonstrated both at the level of macrobiota, which are able to be seen by the naked eye, and microbiota, or microscopic organisms.

They found that, after controlling for other factors, the land-use types lived in by the adolescents had a major impact on the prevalence of allergies, as did species richness of native flowering plants in the area in which they lived.

At the level of microbiota, they found that there were more diverse bacteria and more anti-inflammatory bacteria on the skins of subjects who lived in areas that were forested or agricultural, compared to those who lived in either built-up areas or near bodies of water.

The importance of species richness

The connection between biodiversity and reduced allergic prevalence was particularly associated with the species richness of native flowering plants, although the exact mechanism behind this is not yet clear.

“The mechanisms underlying these associations remain to be clarified, but their implications are profound,” says Hanski.
“Interactions with natural environmental features not only may increase general human well-being in urban areas, but may also enrich the commensal microbiota and enhance its interaction with the immune system, with far-reaching consequences for public health.” (Commensal microbiota are living microbes that live on another organism, such as human skin, without causing any harm.)

So if biodiversity and the prevalence of bacteria have the effect of reducing the likelihood of developing allergic reactions, what does Hanski make of the use of chemicals and fertilisers in agricultural areas, which are widely used to kill a vast array of organisms, and the subsequent consequences for biodiversity?

“There are many aspects of industrialized agriculture that are harmful for biodiversity,” says Hanski, “including the use of chemicals in pest control, fertilizers and general intensive land use.”

Encouraging natural green space

Another implication arising from the study is the type and extent of outdoor areas that are provided in urban areas. “Green space should become an essential part of urban planning, as it already is in some parts of the world,” Hanski says.

However, neatly-mowed lawns are not what he has in mind: “We should start thinking beyond conventional city parks. We should value semi-natural vegetation and stop managing it,” he says.

“Green roofs are another interesting option, and so are food co-operatives, whereby people in towns and cities can grow vegetables for their own use.”

Given that many people do live in urban areas away from both forests and agricultural areas rich in biodiversity, what can they do to protect their immunity and increase their exposure to bacteria?

“Make sure young children have all the time and opportunity they want to play out-of-doors, and encourage them to do so,” he says. “Give them more freedom to play in places with soil and vegetation.”

The hygiene hypothesis

Hanski has some further advice for parents who use anti-bacterial cleansers in their homes with no particular reason for doing so: STOP!

“People don’t realise that the vast majority of bacteria and other microbes are beneficial to us, we could hardly survive without them. Our own bodies have about ten times more bacterial cells than our own cells, and there is now increasing recognition that the bacterial genes and gene products interact with our own genes and gene products, not only in immune responses but in a wide range of biological processes.”

He says that the ‘hygiene hypothesis’ , which suggests that lack of exposure to bacteria and other organisms precipitates the incidence of disease by suppressing the development of the human immune system, is gaining wide acceptance.

However, he says this hypothesis needs to be extended to take into account the wider environment outside of the home, with evidence that more vegetated habitats endow particular benefits on immune function.

Biodiversity on a crowded planet

Given that the study’s authors advocate for the retention of natural vegetation, a further question raised is the effect of population growth and the pressures it places on biodiversity through the need to provide more and more land to house people. What are the consequences of this growth for human health?

“Far too high human population size globally and far too high population density in many parts of the world are two of the root problems, not only for public health, but for the emerging environmental catastrophe in general,” Hanski says.

“Another major problem is, of course, the far too high per capita resource use in developed countries.”

He also laments the lost opportunities to fix these global environmental problems, on the day that the Rio+20 United Nations Conference on Sustainable Development is to commence.

“It is sad that the Rio+20 meeting will not come into agreement on issues that really matter in the long term,” he says.

As Hanski says, “By 2050, some predict that two-thirds of the global human population will live in urban areas with little green space and limited contact with nature and biodiversity.”

The implications of this dire prediction for both human health and biodiversity cannot be underestimated. One can only hope that the results of this study showing an irrefutable interaction between natural environments and human immune function are taken on board before it is too late.

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