Still following the comment made above about the immune system its worth noticing the biodiversity hypothesis below made by a Finish researcher. On this context, it is also worth remembering the posts of March-April of 2019 "Will pandemics or bioterrorism reverse the urbanization rate ?"
"...environments rich in microbial diversity confer protection against autoimmune diseases...Living in dense urban environments might, therefore, lead to an ‘immune adaptation syndrome..."
