In the late 1800s in the United States, babies started developing scurvy; there was a veritable plague. It turned out that the vast majority of victims were being fed milk that had been heat treated (as suggested by Pasteur) to control bacterial disease. Pasteurization was effective against bacteria, but it destroyed the Vitamin C.
From a history of nutrition. Now children are probably getting all sorts of immune disorders, such as hay fever, for the same core reason: fear of bacteria.