Bringing the forest to daycare can boost the young immune system


Would you like to strengthen your children’s immune system? Try to let them play in the dirt more often, according to a new study.

Researchers in Finland found that preschoolers’ immune function changed for the better when they brought nature to daycare playgrounds – including forest floor and vegetation. In simple terms, it shifted to a less inflammatory state.

This redirection of the immune system was also accompanied by some changes in the children’s microbiome – the huge collection of bacteria and other microbes that naturally live on and in the body. Studies have shown that these errors are of crucial importance in normal body processes – from metabolism and brain function to regulation of the immune system.

It’s too early to know if bringing the forest to urban playgrounds has any real health benefits, experts said.

However, the results speak for a regular, messy time outdoors.

“I strongly recommend letting children play in the dirt,” said lead researcher Aki Sinkkonen from the Institute for Natural Resources Finland in Turku.

The study, published online October 14 in Science Advances, emerged from a series of research into modern life and immune function. For example, many studies have found that living on a farm – especially in childhood – is associated with a lower risk of allergies. Meanwhile, the ins and outs of modern life – from antibacterial soaps to processed foods to the widespread use of antibiotics – are believed to reduce the diversity in the body’s microbial communities.

In general, researchers believe that the greater the diversity in the microbiome, the better.

Sinkkonen’s team decided to test the notion that adding “biodiversity” to an urban environment could increase the diversity of children’s microbiomes and alter their immune function.

The researchers recruited 10 urban day-care centers with a total of 75 children aged 3 to 5. In four centers, the researchers transformed gravel playgrounds with forest floors and lawns, planters for growing annuals and peat blocks for children to climb.

The rest of the centers served as a comparison. Three were “close to nature” centers, where small children were regularly taken on excursions into the nearby forests. The other three gravel pitches were the norm.

After a month, children in centers that imported the forest showed an increased diversity of certain bacteria on the skin. That made them more like the children in the nature-oriented centers, the study’s authors explained.

In contrast, skin bacterial diversity in children in standard daycare generally decreased, the results showed.

In the meantime, the green playgrounds have also changed children’s immune systems. Her blood samples showed an increased ratio of an immune system anti-inflammatory protein called IL-10 to an anti-inflammatory protein called IL-17A.

Jack Gilbert, a microbiome researcher who was not involved in the study, praised his “holistic” approach. But he also had reservations.

“They had a very small sample size and had little impact,” said Gilbert, a professor in the University of California at the San Diego School of Medicine.

The tactic, he said, needs to be tested in more schools and involve a lot more children.

And the ultimate question, Gilbert said, is whether children can get health benefits – like a lower risk of eczema or food allergies.

Gilbert doubted that the limited changes in the microbiome were responsible for the findings of the immune system. Instead, he believes it was going the other way: the children’s time digging in microbe-rich dirt changed their immune systems, and that optimized the body’s microbiome.

“For me the most important finding is the change in the immune system,” said Gilbert.

While many questions remain unanswered, he reiterated Sinkkonen’s advice on young children’s playtime. “I think being in the dirt is good,” said Gilbert.

Sinkkonen noted that in this study, the microbial diversity in the top soil layer appeared to be critical. And children actively played in it – dug around, planted vegetation. So it is unlikely, Sinkkonen said, that it would be enough to just drop some grass and bushes.

The researchers plan to pursue the issue of health benefits further. Sinkkonen said they are starting a study to find out if exposing babies to more biodiversity for 10 months can reduce the risk of allergies.

More information

The Harvard School of Public Health is more concerned with the human microbiome.

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