More evidence that dirt and bacteria are good for kids

I read this study which was just published this month that provides further evidence that dirt and bacteria are good for kids. In fact it is the first double blind placebo controlled trial to test the “hygiene hypothesis”.

It’s a small study but it’s certainly informative. They basically took two groups of children age 3-5 (13 in each group), and got them to play in two different sandboxes twice a day for 2 weeks. One sandbox had microbiologically diverse soil and one had soil without many microbes. They took skin and gut bacterial samples as well as blood tests before and after the study, and showed that those in the microbiologically diverse soil had richer and more diverse gut and skin microbiomes, and also changes in immune cells for the better. They also noted that 28 days later, the skin microbiome in the intervention group still differed compared to baseline.

They note that “The findings support the biodiversity hypothesis of immune-mediated diseases” which is essentially the hygiene hypothesis; microbes modulate the immune system to protect kids from immune dysregulation such as in allergies, asthma etc, and one reason for ever-increasing rates of these diseases is the over-obsession with cleanliness and chemicals that kill beneficial microbes. The study also shows that it could be relatively simple to help inoculate kids with these microbes, for example by adding them to playgrounds that kids spend time in regularly. How amazing would it be if our bland sterilized urban environments were instead rich, green and full of healthy microorganisms?

It adds to existing epidemiological evidence, for example that kids who live on farms suffer less asthma/allergies, and evidence of plausible mechanisms to make the solid case that people require microbial diversity for a healthy immune system.

If you have kids, what should you do? The main things are to get outside, play in the soil, go to farms, maybe get a pet. This is easier when you live in the countryside, like I do, but even in urban environments effort can be made to seek out this microbial richness. As usual, evidence supports the benefits of living in harmony with nature and our evolutionary lineage!


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