Vitamin K is a group of 2-methilo-naphthoquinone derivatives. It is a human vitamin, lipophilic (i.e. soluble in lipids) and therefore hydrophobic (i.e. insoluble in water). It is needed in the synthesis of proteins required for blood coagulation. Normally it is produced by bacteria in the intestines, and dietary deficiency is extremely rare unless the intestines are heavily damaged. Vitamin K is involved in the formation of calcium-binding groups in proteins. These calcium-binding groups are called Gla-residues, and the proteins containing these residues are designated as Gla-proteins.
Vitamin K prevents calcification of arteries and other soft tissue. Calcification of organs and other soft tissue is an adverse consequence of aging. The vascular system can suffer such damage that valve replacement and coronary artery bypass procedures may become necessary. Vitamin K prevents elevations in IL-6. Rising levels of interleukin-6 (IL-6) are an indication of aging. A chemical messenger for the immune system, IL-6 promotes inflammation. With aging this cytokine takes over and causes unwarranted inflammation throughout the body, including joints and brain. Alzheimer's patients have highly elevated levels of IL-6 in their brains. Vitamin K regulates the body's calcium and promotes bone calcification. Abnormal calcium accumulation can damage the brain. In fact, changes seen in Alzheimer’s disease reflect disturbances in calcium metabolism. The pineal gland and the kidneys are especially vulnerable to excess calcium infiltration, while the skeleton suffers from a lack of calcium. Vitamin K may play a role in the regulation of blood sugar. The pancreas, which makes insulin, has the second highest amount of vitamin K in the body. In the first study of its kind, Japanese researchers found that vitamin K deficiency can have effects similar to diabetes.
There are three notable forms of Vitamin K, K1 (phytonadione/phylloquinone/phytonactone), K2 (menaquinones), which can be formed by natural bacteria in the intestines, and K3 (menadione), the most active synthetic form of the preparations K3-K7. Absorption of K1 is from the gut (duodenum and jejunum) via the lymphatic system. Conditions that impair lipid absorption will also impair the absorption of Vitamin K, especially antibiotics. In their effort to rid foreign bacteria, antibiotics destroy the normal intestinal flora needed for Vitamin K synthesis, causing a deficiency of the vitamin. Since it is produced in the intestines, it cannot qualify as an official vitamin. Excretion of absorbed Vitamin K occurs mainly in the feces (30-40%), but there is some excreted in the urine (15%) as well.
Menaquinones have side chains composed of a variable number of unsaturated isoprenoid residues; generally they are designated as MK-n, where n specifies the number of isoprenoids.
It is generally accepted that the naphthoquinone is the functional group, so that the mechanism of action is similar for all K-vitamins. Substantial differences may be expected, however, with respect to intestinal absorption, transport, tissue distribution, and bio-availability. These differences are caused by the different lipophilicity of the various side chains, and by the different food matrices in which they occur.