Vitamin K is a group of structurally similar, fat-soluble vitamins the human body requires for complete synthesis of certain proteins that are prerequisites for blood coagulation that the body needs for controlling binding of calcium in bones and other tissues. The vitamin K-related modification of the proteins allows them to bind calcium ions, which they cannot do otherwise. Without vitamin K, blood coagulation is seriously impaired, and uncontrolled bleeding occurs. Low levels of vitamin K also weaken bones and promote calcification of arteries and other soft tissues.
Chemically, the vitamin K family comprises 2-methyl-1,4-naphthoquinone (3-) derivatives. Vitamin K includes two natural vitamers: vitamin K1 and vitamin K2. Vitamin K2, in turn, consists of a number of related chemical subtypes, with differing lengths of carbon side chains made of isoprenoid groups of atoms.
Vitamin K1, also known as phylloquinone, phytomenadione, or phytonadione, is synthesized by plants, and is found in highest amounts in green leafy vegetables because it is directly involved in photosynthesis. It may be thought of as the “plant” form of vitamin K. It is active as a vitamin in animals and performs the classic functions of vitamin K, including its activity in the production of blood-clotting proteins. Animals may also convert it to vitamin K2.
Bacteria in the colon (large intestine) can also convert K1 into vitamin K2. In addition, bacteria typically lengthen the isoprenoid side chain of vitamin K2 to produce a range of vitamin K2 forms, most notably the MK-7 to MK-11 homologues of vitamin K2.
Vitamin K is known as the “blood-clotting vitamin” for its important role in healing wounds. The “K” is derived from the German word koagulation. Vitamin K also plays an important role in bone health.
Bacteria in the gastrointestinal tract naturally make vitamin K. Dietary sources of vitamin K include green leafy vegetables — collards, green leaf lettuce, kale, mustard greens, parsley, romaine lettuce, spinach, Swiss chard and turnip greens — as well as vegetables such as broccoli, Brussels sprouts, cauliflower and cabbage. Other sources that are less rich in vitamin K include meats, fish, liver, eggs and cereals.
Vitamin K is an important factor in bone health and wound healing. Vitamin K is a fat-soluble vitamin that makes proteins for healthy bones and normal blood clotting. Vitamin K helps produce four of the 13 proteins needed for blood clotting.
K also teams up with other vitamins. Vitamin K works with vitamin D to ensure that calcium finds its way to the bones to help them develop properly.
Since vitamin K is so integral to good bone health, it is natural to assume that it may be used to treat certain bone problems. Research found that vitamin K has a positive effect on bone mineral density and decreases fracture risk.
Health benefits of vitamin K that have been proposed but not scientifically proven include protection against heart disease, prostate cancer and Alzheimer’s disease.
As mentioned in the Description section, vitamin K is perhaps best known for its role in the blood clotting process. When people hear the term “blood clot,” they might sometimes jump to the conclusion that a blood clot is bad. But there are many times when it is very important for our blood to clot. For example, blood clots are necessary to stop bleeding when our skin gets punctured.
Yet at the same time, people are correct when they say that blood clotting can cause problems. For example, if the inside of a blood vessel has become too narrow due to the buildup (over time) of plaque, this plaque can sometimes rupture and our body may form a blood clot in order to seal off the ruptured plaque. However, this blood clot might also end up stopping the flow of blood through the blood vessel since the blood vessel had become overly narrowed from the buildup of plaque.
Regardless of the specific situation, vitamin K is necessary for blood clots to form. The clotting process is very complex, requiring at least 12 proteins to function before the clotting process can be completed. Four of these protein clotting factors require vitamin K for their activity.
Luckily, we rarely see vitamin K deficiency lead to impairment in the clotting process in adults. We see it in newborns because vitamin K does not efficiently cross the placenta to the fetus, and it can take several weeks for the fetus to build up dietary stores. We also occasionally see clotting problems related to vitamin K deficiency in persons with severe liver or gastrointestinal diseases. But *vitamin K deficiency basically never causes insufficient clotting disorders in healthy adults.
In contrast to insufficient clotting in healthy adults, we do see *vitamin K deficiency becoming involved in unwanted clotting. This process once again involves the activity of multiple *vitamin K-dependent enzyme systems, most importantly a system called matrix Gla protein.
*Vitamin K may help keep lower blood pressure by eliminating the build-up of several minerals in the arteries (mineralization), allowing the heart to freely push blood through the body. Mineralization naturally occurs with age and is a major risk factor for heart disease. Adequate intake of *vitamin K has also been shown to lower the risk of stroke.
As we age, calcium that belongs in our bones begins to make its appearance in other unwanted areas, including inside the linings of major arteries. Over time, normal smooth muscle cells in artery walls transform into bone-like cells through the deposition of calcium, essentially turning sections of artery into bony tissue that is not resilient and flexible, and does not have the ability to effectively regulate blood flow. This process lends literal reality to the term “hardening of the arteries,” which we now know as late-stage atherosclerosis.
Nature has provided a powerful inhibitor of arterial calcification in the form of matrix Gla protein, one of the 16 Gla-proteins activated by *vitamin K. This specific Gla-protein is produced in arterial walls, but is only activated when sufficient *vitamin K is present. In the absence of sufficient *vitamin K, arterial calcification is able to continue unopposed, leading to advanced atherosclerosis and its deadly consequences, heart attacks and strokes. Indeed, in older men and women who had the highest levels of inactive matrix Gla protein (indicating low *vitamin K levels), there was a nearly 3-fold increased risk of cardiovascular disease compared to those with the lowest levels.
Another way matrix Gla proteins help protect against atherosclerosis is by inhibiting the production of inflammatory signaling molecules (cytokines), which contribute to plaque formation and calcification. People with the highest dietary intake of *vitamin K have significantly lower levels of those inflammatory markers, and also of substances involved in appetite generation and insulin resistance, both of which are important in preventing atherosclerosis.(Some of these effects may be related to increased levels of another *vitamin K-dependent Gla-protein that suppresses inflammation and promotes glucose tolerance).
Deficiency and dosage
*Vitamin K deficiency is rare in the United States. Typically, those afflicted with a deficiency are unable to properly absorb the *vitamin K made naturally in the intestinal tract. People who have severe gastrointestinal disorders, such as gallbladder disease, cystic fibrosis, celiac or Crohn’s disease are unable to properly absorb *vitamin K, so they are more susceptible to being deficient. *Vitamin K supplements are useful for these medical conditions.
Those who take antibiotics for an extended period of time can also experience a lack of *vitamin K, according to the NLM. Antibiotics kill the bacteria that create *vitamin K.
Babies are not born with the bacteria that create *vitamin K, and breast milk is not a good source of the vitamin. Newborn babies in many developed countries are given shots of *vitamin K to prevent internal and external bleeding.
Deficiency can cause excessive bleeding, which may start from the nose or gums. Other symptoms can include easy bruising, blood in urine and stools. Those experiencing a lack of *vitamin K may be instructed by their health care professional to take a supplement.
The recommended daily allowance (RDA) for *vitamin K varies depending on age, gender, weight and several other factors. However, the suggested RDA is typically 70 to 90 micrograms (mcg) for adults, according to the NLM. The National Health Service of the UK (NHS) states that, every day, adults need approximately 0.001 milligrams (mg) — or 1 mcg — of *vitamin K for every kilogram (2.20 lbs.) of body weight. So, a person who weighs 150 lbs. (68 kg) should get 68 mcg of *vitamin K a day.