Discovery of Vitamin B12

B12 deficiency is the cause of pernicious anemia, an anemic disease that was usually fatal and has unknown etiology when it was first described in medicine. The cure, and B12, were discovered by accident. George Whipple had been doing experiments in which he induced anemia in dogs by bleeding them, and then fed them various foods to observe which diets allowed them fastest recovery from the anemia produced. In the process, he discovered that ingesting large amounts of liver seemed to most-rapidly cure the anemia of blood loss. Thus, he hypothesized that liver ingestion might treat pernicious anemia. He tried this and reported some signs of success in 1920.

After a series of careful clinical studies, George Richards Minot and William Murphy set out to partly isolate the substance in liver which cured anemia in dogs, and found that it was iron. They also found that an entirely different liver substance cured pernicious anemia in humans, that had no effect on dogs under the conditions used. The specific factor treatment for pernicious anemia, found in liver juice, had been found by this coincidence. Minot and Murphy reported these experiments in 1926. This was the first real progress with this disease. Despite this discovery, for several years patients were still required to eat large amounts of raw liver or to drink considerable amounts of liver juice.

In 1928, the chemist Edwin Cohn prepared a liver extract that was 50 to 100 times more potent than the natural liver products. The extract was the first workable treatment for the disease. For their initial work in pointing the way to a working treatment, Whipple, Minot, and Murphy shared the 1934 Nobel Prize in Physiology or Medicine.

These events in turn eventually let to discovery of the soluble vitamin, called vitamin B12, in the liver juice. The vitamin in liver extracts was not isolated until 1948 by the chemists Karl A. Folkers of the United States and Alexander R. Todd of Great Britain. The substance proved to be cobalamin—the most complex of all the vitamins. It could also be injected directly into muscle, making it possible to treat pernicious anemia more easily

Dorothy Hodgkin completed the elucidation of B12's chemical structure by using x-ray crystallography, receiving the 1964 Nobel Prize in chemistry for her work. Vitamin B12 was finally synthesized by Robert Burns Woodward in 1971, after a ten year effort.