In most large cities in the Northern hemisphere in the late 19th and early 20th centuries, rickets was an enormous public health problem, mainly because exposure to sunlight was limited, particularly for children.1 German physicians noticed that daily administration of a tablespoon of cod liver oil could reverse rickets, a finding that led to the discovery of vitamin D, its structure, and function. In the United States, most of the milk supply is now voluntarily fortified with vitamin D, whereas fortification of infant formula with vitamin D is mandatory.2 In many European countries, food fortification with vitamin D is not required by law,3 but vitamin D administration to infants and pregnant women is recommended. This public health intervention has been highly successful and has made rickets a rare disease.
von Mutius E, Martinez FD. Inconclusive Results of Randomized Trials of Prenatal Vitamin D for Asthma Prevention in OffspringCurbing the Enthusiasm. JAMA. 2016;315(4):347-348. doi:10.1001/jama.2015.18963