The existence of vitamin K1 was first demonstrated by the Danish scientist Henrik Dam in early '30 of the 20th century. He was studying diets in chickens and noticed that his flock was suffering from frequent haemorrhages. He postulated that there had to be a factor in the diet which prevented the bleedings.
After extensive research this unknown substance was identified, and named factor K – K for the Danish word for coagulation. The nature of this vitamin was revealed several years later – in 1939 – by another scientist, Professor Edward A. Doisy of St. Louis University School of Medicine, US. He was able to describe the molecular structure of this K factor, and to synthesise not only one molecule but several closely related molecules. In this way it was discovered that vitamin K consisted of two groups of molecules; K1 and K2.
In relation to biological effects, it is important to be aware that the molecular difference between K1 and K2 gives different biological properties. K1 represents only one molecular form, while vitamin K2 represents several molecules. However, only two forms of vitamin K2 (MK-4 and MK-7) have been scientifically investigated and are presently commercially available.