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Day guards in Finland built “forest roads” and changed children’s immune systems.

Within 30 days of playing in forest soil and leaf litter, Finnish preschoolers had increased the number of T-cells and much more varied gut bacteria.
In a fascinating experiment, Finnish researchers have recreated the environment on a forest floor on the playgrounds in four urban nurseries.
They covered the playgrounds with forest soil, moss, meadow grass, dwarf heather, blueberries and crowberries and installed planting boxes for annual garden crops.
Childcare workers instructed the preschool-age children to play in the greenery and the soil for an hour and a half a day for a month.

Their gut and skin microbes were analyzed before and after the experiment and compared to children from normal urban nurseries with regular sterile playgrounds.
After just 28 days, the diversity of their gut and skin bacteria increased dramatically, as did their T-cell numbers and other important immune markers in the blood.
It supports the hypothesis of biodiversity and the concept that low biological diversity in the modern living environment can lead to an uneducated immune system and thus increase the incidence of immune-borne diseases