More info; https://en.wikipedia.org/wiki/Body_earthing
This especially;
"Earthing can be regarded as a new medical idea, but it is an old practice. The use of isolating shoe soles (of rubber and plastic) started around the middle of the 20th century. Leather soles, used for some thousand years, give a partial earthing – at least when moistened by sweat.
Sleeping in beds with fully isolating synthetic mattresses is also a modern practice, while getting a partial isolation through using wooden beds, perhaps combined with multi-floor buildings, has a tradition extending a few thousand years back.
Earthing has consequently been the natural lifestyle throughout almost all the time humans have existed, and even modern activities like swimming and walking barefoot in the grass will give thorough earthing. This means the modern earthing idea doesn't lead to new or unnatural practices."
