Vitamin K (K from "Koagulations-Vitamin" in German and Scandinavian languages) denotes a group of lipophilic, hydrophobic vitamins that are needed for the posttranslational modification of certain proteins, mostly required for blood coagulation. Chemically they are 2-methyl-1,4-naphthoquinone derivatives.

Vitamin K1 is also known as phylloquinone or phytomenadione (also called phytonadione). Vitamin K2 (menaquinone, menatetrenone) is normally produced by bacteria in the Large Intestine, and dietary deficiency is extremely rare unless the intestines are heavily damaged, are unable to absorb the molecule, or due to decreased production by normal flora, as seen in broad spectrum antibiotic use.

There are three synthetic forms of vitamin K, vitamins K3, K4, and K5, which are used in many areas including the pet food industry (vitamin K3) and to inhibit fungal growth (vitamin K5)

Vitamin K and bone health

Recently vitamin K has also been lauded for its potential role in the increase of bone mass. Studies have proved that supplemental vitamin K promotes osteotrophic processes and slows osteoclastic processes via calcium bonding. In Japan, a form of vitamin K2 is recognized as a treatment for osteoporosis. However the long term effects and benefits are unknown and it remains controversial.[citation needed] Data from the 1998 Nurses Health Study found an inverse relationship between dietary vitamin K1 and the risk of hip fracture. After being given 110 micrograms/day of vitamin K, the main results showed that women who consumed lettuce one or more times per day had a significantly lower risk of hip fracture than women who consumed lettuce one or fewer times per week. In addition to this, high intakes of vitamin D but low intakes of vitamin K may still pose an increased risk of hip fracture hinting at a relationship between these two vitamins.

Other studies have shown that Vitamin K-antagonists lead to early calcification of the epiphysis and epiphysial line in mice and other animals, causing seriously decreased bone growth. This is due to defects on osteocalcin and matrix gla protein. Their primary function is to avoid overcalcification of the bone and cartilage. Vitamin K is important in the process of carboxylating glutamic acid (Glu) in these proteins to gamma-carboxyglutamic acid (Gla), activating the protein.

Vitamin K and Alzheimer's disease

Research into the antioxidant properties of vitamin K indicates that the concentration of vitamin K is lower in the circulation of carriers of the APOE4 gene and recent studies have shown its ability to inhibit cell death due to oxidation in nerve cells. It has been hypothesized that vitamin K may have an effect on neuronal damage and that supplementation may hold benefits to treating this disease, although more research is necessary in this area.

Vitamin K used topically

Vitamin K may be applied topically, typically as a 5% cream, to diminish postoperative bruising from cosmetic surgery and injections, broken capillaries (spider veins), to treat rosacea and to aid in the fading of hyperpigmentation and dark under-eye circles.

Vitamin K and cancer

While researchers in Japan were studying the role of vitamin K2 in the prevention of bone loss in females with liver disease, they discovered another possible effect of this phytonutrient. This two year study which involved 21 women with viral liver cirrhosis found that women in the supplement group were 90 percent less likely to develop liver cancer [48][49] A German study performed on men with prostate cancer found a significant inverse relationship between vitamin K2 consumption and advanced prostate cancer

Vitamin K as antidote for poisoning by coumarins

Vitamin K is a true antidote for poisoning by coumarins such as bromadiolone, which are commonly found in rodenticides. Coumarins possess anticoagulatory and rodenticidal properties because they can completely block synthesis of Vitamin K in the liver, especially in rodents. Death is usually a result of internal hemorrhage. Treatment usually consists of repeated intravenous doses of Vitamin K, followed by doses in pill form for a period of at least two weeks, though possibly up to 2 months, afterwards. If caught early, prognosis is good, even when great amounts are ingested.