Vitamin K is a group of fat soluble, structurally similar vitamins having methylated naphthoquinone ring. It is sometimes also referred as antihemorrhagic factor, menaquinone or phylloquinone. The vitamin K has got its name from a German word “koagulation.” This vitamin was discovered by Henrik Dam and he was awarded Noble Prize for his discovery.

This group of vitamins includes two natural: vitamin K1 and vitamin K2, and three synthetic vitamins: K3, K4 and K5. Natural forms (K1 and K2) are non toxic while synthetic K3 (menadione) has shown some type of toxicity to human. Vitamin K1 (also termed as Phylloquinone) is present in green plants. While vitamin K2 (menaquinone) is present in animal foods like dairy products, meat, fish, egg and cheese. These both naturally occurring vitamin types have their own roles in the body. Vitamin K1 plays a vital part in blood clot formation while vitamin K2 is important in bone, dental and heart health.

Vitamin K2 has several subtypes. Vitamin K2 homologs or Menaquinones (MK) are characterized by isoprenoids (sometimes called terpenoids, naturally occurring organic compounds) residues in their side chains. MK-n is an abbreviated form of menaquinones, n stands for the number of terpenoids side chain residues. For example, MK-7 (abbreviation of Menaquinone-7) has seven terpenoids side chain residues. Menaquinone have several forms but two subtypes menaquinone-4 (MK4) and menaquinone-7 (MK7) are studied extensively. Biochemical studies have shown that MK-7 is not produced by human tissues, so it is different from MK-4 in that sense.

MK4 is produced by conversion of vitamin K1 by gastrointestinal anaerobic bacteria. Some studies suggest that this conversion takes place in the testes, pancreas, and in arterial walls. Still, there is a debate on biochemical transformation of vitamin K1 to MK-4.

Vitamin K has been classically associated with blood coagulation. Vitamin K (VK) serves as coenzyme for VK-dependent carboxylase.  Research studies have shown that VK is required in the formation of numerous proteins called GCGA (γ-carboxy glutamic acid). Vitamin K2 acts as a cofactor in the carboxylation of glutamic acid with the help of an enzyme called (gamma glutamyl carboxylate) to form gamma carboxy glutamic acid (GCGA). Without γ-carboxy glutamic acid the regulation of calcium can’t take place in the body. There are numerous types of GCGA proteins present in the body. Osteocalcin is the most abundant GCGA protein, synthesized by osteoblasts in the bones. It regulates the mineral deposition in the bones and teeth. Without Vitamin K2, this protein is inactivated for the intended function. Thus, VK2 has beneficial effects on bone formation. Studies have demonstrated that VK2 deficiency may result in reduction of bone mass along with hypocarboxylation of osteocalcin.

Research studies in the past showed that vitamin K2 is important for the utilization of minerals in the body, supports growth and development, involved in normal reproduction, protects against arterial calcification which can lead to cardio-vascular diseases and is a major component of the brain. Calcification of the arteries and soft tissues is a major consequence of aging, vitamin K2 MK-4 has shown tremendous protection from osteoporosis and pathological calcification.

Bone is a complex tissue consisting of different minerals like calcium, phosphorous etc. and connective tissues called collagen. The collagen gives flexibility while minerals impart hardness to bones. MK-4 promotes bone health through the formation of bone collagen. Vitamin K2 (MK-4, but not MK-7 or vitamin K1) has also been shown to prevent bone loss and/or fractures.  MK-4 has been an approved treatment for osteoporosis in Japan since 1995. In Japan, MK-4 is still a recognized treatment of osteoporosis. Vitamin K2 MK-4 has shown to decrease fractures up to 87%.

A study conducted in Japan demonstrated that vitamin K2 has the ability to reduce  the risk of liver cancer in patients with viral cirrhosis. The study results showed a 20% less chances of cancer as compared to control group. Geranyl-geraniol was the suggested  substance behind this effect, it is a byproduct of vitamin K2. This substance perhaps induces cell death in tumor and also inhibit cell growth.

As vitamin K is important in the carboxylation of osteocalcin, a protein involved in bone synthesis, so osteoporosis is associated with vitamin K deficiency. Vitamin K2 is essential for healthy arteries and strong bones. Apart from being an excellent calcium regulator, vitamin K2 is also important for skin, brain and prostate health.