I have written on that before but find it striking again when reading another historical perspective.
The first insight into the possible relationship between the industrialization of Northern Europe and rickets was made by Sniadecki in 1822 when he concluded that children who lived in the inner city of Warsaw had a high incidence of rickets because of their lack of sun exposure. This was based on his clinical observations that children living in rural areas outside of Warsaw did not suffer from rickets while children born and raised in Warsaw were plagued with the disease.
Now we are supplementing vitamin D to nearly all inner city children who have a high allergy prevalence but not so much in rural areas where we see less allergy – everywhere, not only in Warsaw.
Did we trade rickets with allergy?