The Nuance

Why Spending Time Around Other Living Things Positively Affects Your Health

Time spent around other living things may be essential to the health of your microbiome, and by extension the health of your brain and body

Illustration: Kieran Blakey

Until about the midpoint of the 20th century, the prevailing view of life on Earth was something akin to a massive interspecies cage match. The English biologist Thomas Henry Huxley famously likened the natural world to a “gladiator’s show […] whereby the strongest, the swiftest, and the cunningest live to fight another day.”

Now we know better.

In his 2020 bestseller Entangled Life, the writer and biologist Merlin Sheldrake details many of the profound and symbiotic relationships that exist among Earth’s life-forms. Fungi are Sheldrake’s field of expertise, and he describes how vast subterranean fungal networks both support and rely on the community of trees and plants that sprout above ground, which are likewise codependent with the insects and animals that live in their midst.

Biologically diverse forests — and oceans, and wetlands, and deserts — are healthier than biologically bereft ones, he explains. Life supports life. And this rule of nature seems to extend to humans and the environments we inhabit.

“Our study found that the diversity of bird species in a place, which is an indicator of overall biodiversity, was associated with higher levels of life satisfaction.”

A 2018 study in Frontiers in Psychology found that “ecologically rich” city parks — defined as those that are home to a large array of plants, insects, and animals — were more relaxing and restorative to visitors than less biologically diverse parks. Another recent study, published last month in the journal Ecological Economics, found a strong association between the number of bird species in a region and the well-being of its residents.

“Our study found that the diversity of bird species in a place, which is an indicator of overall biodiversity, was associated with higher levels of life satisfaction,” says Joel Methorst, PhD, first author of the study and a postdoctoral researcher at Helmut-Schmidt University in Germany. The well-being effects of biodiversity were about as robust as those associated with income, he says.

These findings are consistent with research that has shown time spent in nature, with animals, and among plants seems to benefit a person’s mental and physical health. Taken together, all this work suggests that our health and happiness is at least partly dependent on our exposure to other living things. And microbes may help explain this relationship.

How our environments rub off on us, sometimes literally

Since 1989, when an American immunologist named David Strachan first introduced it, the “hygiene hypothesis” has gained attention and momentum.

In its original form, the hypothesis held that early childhood exposure to germs — meaning infection- or illness-causing microbes — could protect people from sickness later in life, perhaps by strengthening the immune system. Meanwhile, a lack of exposure to these germs could increase a person’s vulnerabilities.

Strachan was onto something. But his original theory has been absorbed into a broader one that some experts have dubbed the “biodiversity hypothesis.” The idea here is that exposure to natural and biologically diverse environments supports human health and well-being by strengthening and enriching our microbiomes.

By some estimates, each one of us is walking around with approximately as many bacterial cells as human cells. We truly contain multitudes. And there’s accumulating evidence that the species of microbes we possess — in our guts, on our skin, and possibly even in our brains — affect how happy and healthy we tend to be. Poor microbial diversity, sometimes referred to as “dysbiosis,” is common in people with both diabetes and inflammatory bowel disease. There’s also evidence linking microbiome health to depression and to a range of neurological disorders.

Exposure to natural and biologically diverse environments supports human health and well-being by strengthening and enriching our microbiomes.

A lot of recent attention has been paid to those drugs or chemicals, such as antibiotics or disinfectants, that may interfere with the health of our microbiomes. There’s also evidence that the stuff we eat affects our bacterial populations, which has led to interest in pre- and probiotics. But new research suggests that the richness of life outside our bodies may be one of the greatest determinants of the richness of life inside us.

A small study, appearing this month in the journal Environmental International, found that when people interacted with urban green spaces — breathing the air, digging in the dirt, and brushing up against leaves and plants — these interactions increased the diversity of microbes on their skin and in their noses. “Our study […] suggests that increased exposure to diverse outdoor environments may increase the microbial diversity, which could lead to positive health outcomes,” its authors write.

This study dovetails with research on people who own pets, who live on traditional farms, who garden, or who spend time in natural environments — all situations that expose us to other living things and their bacteria, and all situations that seem to do us some good. “Our findings start to get at the mechanisms of how spending time outside and with nature may be beneficial for us,” says Laura Weyrich, PhD, co-author of the study and an associate professor of anthropology at Pennsylvania State University.

If the biodiversity hypothesis is borne out, then anything that changes the microbial makeup of our environments or reduces our interaction with nature may contribute to our risk for noncommunicable diseases — including cancer, diabetes, and autoimmune disorders — all of which are on the rise.

Put another way, we may be suffering because our microbial communities are suffering. And our microbial communities may be suffering because the environments in which we live are both more sanitized and less biologically diverse than we need them to be.

The richness of life outside our bodies may be one of the greatest determinants of the richness of life inside us.

Making changes that help the most

In Entangled Life, Sheldrake describes the human body’s prodigious community of microorganisms and the futility of trying to differentiate their “biological identity” from ours. “Our bodies, like those of other organisms, are dwelling places,” he writes. “Life is nested biomes all the way down.”

There are lots of health tips to be gleaned from the biodiversity research, many of which have long been associated with benefits. Spend more time in nature. Take up gardening. Adopt a pet. Eat a varied diet rich in plants and fermented foods.

But while there are ways to increase your exposure to flora and fauna and fungi, and, by extension, increase the richness of your microbial communities, the bigger story — and the more important lesson — may be that the health of our microbes seems to be dependent on the biological health and variety of our environments, which in turn are dependent on the overall health of our planet.

If this is true, then we are each of us little walking and talking Earths. And the sicker our planet becomes, the sicker we’re likely to become, too.

I write about health and science. I live in Detroit with my wife and kids. I’m trying to learn German, but my progress so far is nicht gut.

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