Now there’s another reason to get back to nature. A new study reveals that people who grow up in more-rural environments are less likely to develop allergies. The reason may be that environments rich with species harbor more friendly microbes, which colonize our bodies and protect against inflammatory disorders.

“Contact of people, particularly children, with the natural environment and biodiversity could be really important for the development of the immune system,” says Ilkka Hanski, an ecologist at the University of Helsinki and lead author of the study.

Hanski and his colleagues investigated the idea that the global decline in biodiversity and decreasing human contact with it is linked to the escalating prevalence of chronic inflammatory and autoimmune diseases.

To test whether biodiversity creates a shield against such conditions, the team investigated the microbial diversity in 118 teenagers. The study participants, who had lived in the same houses their whole lives, were chosen at random from an area in eastern Finland. Some lived on rural, isolated farms; others lived in towns. The researchers controlled for factors such as whether family members smoked, if pets lived in the house and to what type of allergens the subjects were sensitive.

The researchers took microbial samples from the participants’ forearms and sequenced the DNA to find which species of microbes were present. They also surveyed all of the types of plants growing around the adolescents’ homes. The participants were part of a separate long-term allergy study, so the researchers took advantage of that data to investigate the connection between biodiversity and allergies.

Although individuals with allergies were found throughout the study area, the authors discovered that the likelihood of allergies was related to the amount of biodiversity around the teenagers’ homes: The more forest and agricultural land, the lower the prevalence of allergies, and those living near bodies of water or in urban centers had significantly higher levels of allergies.

In particular, the researchers report online in the Proceedings of the National Academy of Sciences, the number of species of a certain group of flora — uncommon native flowering plants — was 25 percent higher in the yards of nonallergic teens than in the vicinity of their allergic counterparts. Whether there is something special about Finland’s native plants is an open question, Hanski says. “Many research groups worldwide could easily attain these data from their study populations, and then we’d know how general these results might be,” he says.

In addition to having higher levels of plant biodiversity around their homes, nonallergic individuals sported a larger number of microbial species on their skin. One group of bacteria, called gammaproteobacteria, was especially more prevalent, and one member of this group may be responsible for convincing the immune system to ignore allergens. These types of bacteria seem to play an important role in explaining why children develop allergies or not, says Thomas Abrahamsson, a pediatrician at Linkoping University in Sweden, who was not involved in the study.

Allergies aren’t the only thing at stake here, says Hanski. He thinks the diversity of microbes living with humans “absolutely” influences other diseases, such as Type 1 diabetes, asthma and even depression. “We’re not claiming that contact with nature and biodiversity is the only important thing, but it could be a significant contributing factor,” he says.

This article is from ScienceNOW, the daily online news service of the journal Science.