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.
By Markham Heid.
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.
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.