Vitamin D: A Brief History

Observation of vitamin D deficiency goes back hundreds of years. A common condition known as rickets, a condition characterized by bone deformity and weakness. Tradition held that the best treatment was fresh air and sunlight; to which there was a grain of truth.
 
Near the turn of the twentieth century, experiments focusing on nutrition began to advance. In the early 20s, Vitamin D was the fourth nutritional substance identified, thus assigned the fourth letter of the alphabet.
 
Early experiments connected rickets to the newly discovered vitamin A, but this idea was dismissed when the ability to destroy the vitamin A contained in cod-liver oil was confirmed. This altered cod-liver oil was used to demonstrate that the oil still cured rickets, despite the removal of the vitamin A.
 
The discovery that sunlight-irradiated food, particularly dairy, wheat, and meat, also cured rickets, led scientists to compare the curative effect of several foods before and after irradiation. The results clearly showed that sunlight was the factor which activated the nutritional substance they searched for.
 
The first attempts at isolation brought cholesterol to the forefront, but questions arose regarding the purity of the research sample they prepared. Further progress in the ability to isolate cholesterol ruled the substance out of consideration as the precursor needed to create vitamin D.
 
The search eventually focused on a substance extracted from fungi that showed success in treating rickets in rats, once irradiated. The substance was isolated in 1932, and vitamin D2 (ergocaliferol) had been discovered.
 
However, this substance was only found in plants, which left the similar function observed in animals unsolved. Eventually, a substance found in hog skin was irradiated to form the familiar form of vitamin D3 produced by humans, cholecalciferol.

TIMELINE:

1645: Earliest known scientific description of vitamin-D deficiency defines rickets.
 
1824: Cod-liver oil first prescribed as a treatment for rickets.
 
1914: First scientific attempt to isolate the curative substance in cod-liver oil results in the identification of the substance that would become vitamin A.
 
1919: Scientific proof of rickets’ association with dietary deficiency. Artificial light (containing UV radiation) first used to cure rickets.
 
1920: Method to destroy vitamin A in liquids found.
 
1922: Cod-liver oil with vitamin A removed still cures rickets. Curative substance dubbed vitamin D.
 
1924: Irradiation of food found (in particular flesh, milk, and wheat, among others) shown to cure rickets.
 
1925: Cholesterol becomes significant in search for vitamin D precursor.
 
1926: Focus of search shifts to unnamed substance closely associated with cholesterol when purified cholesterol fails to cure rickets.
 
1932: Vitamin D2 (ergocaliferol) was chemically characterized.
 
1936: Calciferol chemical structure completed.
 
1937: Substance in hog skin successfully isolated and irradiated to create cholecalciferol, vitamin D3.
 
1955: Natural production of ergocalciferol in plants fully described.
 
1980: Natural production of cholecaliferol in animals completely described.