Vitamin A discovered
A number of researchers were studying the nutritional requirements of mammals in the early 1900’s. Experiments were carried out on the diets of young rats and mice, beginning with simple dietary mixtures and finding out what more was needed. For a long time researchers thought that failures in growth resulted from ingredients in the diet becoming denatured.
The first clear evidence that a lack of particular components of the diet could be harmful was presented in 1912 by Gowland Hopkins, who had previously isolated and demonstrated the essential nature of the amino acid tryptophan.
He fed young rats on casein, lard, sucrose, starch and minerals. Half of the rats also received milk daily. Those receiving the milk grew well, and after two weeks the group receiving the milk was switched. He found that those receiving the milk grew normally and those now lacking did not continue to develop well. He explained this by the basic diet was lacking in some essential organic nutrient, and felt that similar problems may be present in human diseases related to diet.
Hopkins did not investigate his “milk factor” further, but a researcher in the USA, Elmer McCollum found that given a purified diet rats began to loose weight after 10 weeks, but would recover if given butter fat, but not olive oil. In 1914 he found that the active component could be separated from the rest of the butter fat, as it was soluble in ether. He called this nutrient “factor A”. He termed a nutrient which had been isolated from rice polishings by Casimir Funk in 1911 “factor B”. These fat soluble factors were later to become vitamins A and B, a term coined by Casimir Funk as a contraction of “vital amine”. It was subsequently found that not all vitamins are amines.
Vitamin deficiency in both humans and rats causes malnutrition and deficiency of vitamin A can result in serious eye damage.