Vitamin K is a fat soluble naturally occurring vitamin together with three other vitamins. These are:

  • Vitamin A
  • Vitamin D
  • Vitamin E

Unlike these other vitamins that have the potential to accumulate in the body and cause toxicity, vitamin K is stored in very low amounts. For this reason, it has to be replenished on a regular basis because the body reserves are usually depleted fast. Fortunately, the body has a mechanism where some amounts of the vitamin can be recycled over and over again to continue with its functions. Could this be the reason why even in severe starvation, bleeding (from lack of the vitamin) is usually not a common symptom?

The relative low levels of vitamin K are due to its fast metabolism and excretion. It is thought that only about 30-40% of a dose taken orally is retained in the body. The other part is quickly eliminated in urine and stools.

Functions of vitamin K

This vitamin was identified a long time ago to be an important factor in the regulation of blood clotting mechanism. There are a number of clotting factors and vitamin K is needed for the functions of clotting factor 2 called prothrombin. Without it, blood will not clot in time and the possibility of bleeding severely is real. But the vitamin has other functions in the body that include:

  • It is a cofactor for an enzyme needed for the metabolism of glutamic acid.
  • It helps in the metabolism of calcium
  • It is an important nutrient for bone-health.
  • It plays a role in growth regulation, cell signaling and biologically determined cell death (apoptosis)

Types of vitamin K

There are natural and synthetic preparations of vitamin K.
Natural types are:

  1. Phylloquinones or simply vitamin K1. This is the predominant form of the natural form and it is abundant in many green and leafy vegetables.
  2. Menaquinones or vitamin K2. Depending on their structure, these are further subdivided into MK4 to MK13. Not all these subtypes have been studied fully but MK4, 7 and 9 are well researched. Interestingly, MK4 can be synthesized from phylloquinones without the activity of any bacteria. The vitamin is produced by bacteria activity as in fermented foods and some are found in animal sourced products.

    MK4 can also be synthesized from the synthetic form of vitamin K menadione after it is converted in the body.

Synthetic vitamin K is called menadione (vitamin K3) and it is mostly used in animal feeds. For it to be biologically available, it has to be converted to menaquinone. Vitamin K4 and K5 are also synthetic and are mostly used as industrial products.

Symptoms of vitamin K deficiency

Vitamin K is uncommon in adults. Subtle deficiency can be suspected if laboratory tests show prolonged clotting time. Common symptoms include:

  • Easy bruising and bleeding
  • Heavy menses
  • Blood in stools. Maybe frank blood or digested blood (melena stools) or themicroscopic type (occult blood)
  • Bleeding gums
  • Blood in urine
  • In neonates and infants intracranial bleeding can quickly prove fatal

Factors that increase risk of vitamin K deficiency

  1. Premature babies. The clotting mechanism for these babies may not be fully developed and their vitamin K stores may be very low.
  2. Babies who have not been given vitamin K injection at birth. This shot is recommended by the American Academy of Pediatrics. Opponents of this shot argue that there is a chance that the injection increases the risk of childhood leukemia and other cancers. Other research suggests this is not the case.
  3. Those patients on vitamin K antagonists such as warfarin.
  4. Extensive liver disorders and damage
  5. Malabsorption syndrome
  6. Cystic fibrosis patients.

Vegan sources of vitamin K

There are three main sources of vitamin K. these are from food, from nutritional supplements and from bacterial activity in the gut. Food sources include:

  • Kale
  • Broccoli
  • Cotton seed oil
  • Spinach
  • Lettuce
  • Soybean oil

In the U.S both forms of natural vitamin K supplements, menaquinones and phylloquinones are available as over the counter health products.

Specific health benefits of vitamin K

  1. Helps our blood to remain in the vessels and when we get cuts, we don’t bleed endlessly but the vitamin in conjunction with other clotting factors seal the injured vessels and effectively stops the bleeding.
  2. Lowers the risk of insulin-dependent diabetes mellitus (type 2 diabetes). A study found that people with adequate intake of vitamin K had low biomarkers for that type of diabetes.
  3. Keeps blood vessels supple, patent and healthy. With age, or in some disease situations, calcium is deposited in tissues and blood vessel lining which leads to hardening. This is called atherosclerosis. Vitamin K helps to activate a protein called matrix Gla protein that naturally inhibits calcification of blood vessels. This in turn lowers the risk of cardiovascular events by several folds. One study published in the Maturitas of February 2014 found that the risk in the aged with adequate vitamin K was reduced by up to three times compared to those with deficiency of the vitamin.
  4. Helps to maintain healthy bones. Vitamin K is needed to activate Gla osteocalcin proteins. This is vital to maintain properly bound minerals in the bones. Low vitamin K increases the risk of osteoporosis (brittle bones).
  5. Lowers the risk of cancer. One study has suggested that sufficient vitamin K can help to lower the risk of some cancers. These includes colon and prostate cancers
  6. Has been found to offer longevity benefits. This may be as an overall benefit of the many other benefits put together. People with high risk factors for cardiovascular disorders but who had high vitamin K intake were found to be up to 36% less likely to die from whatever cause than those who had low intake.

Safety of vitamin K

Dietary sources are safe and there is no likely risk associated with vitamin K rich foods. Nutritional supplements containing the natural forms of vitamin K are safe. The synthetic form, menadione, has been associated with serious toxicity issues. These include impairment of glutathione(a powerful antioxidant), jaundice, cell membrane oxidative damage and hemolytic anemia.

Vitamin K can interact with a number of medications and so people on any type of medicines should talk to their doctor before taking the vitamin. The vitamin crosses the placenta barrier and so pregnant mothers and those breastfeeding should consult their gynecologist and pediatrician respectively before using vitamin K supplemnts.


DiNicolantonio, J. J., Bhutani, J., & O’Keefe, J. H. (2015). The health benefits of vitamin K. Open Heart, 2(1), e000300.

Rishavy, M. A., Hallgren, K. W., Wilson, L. A., Usubalieva, A., Runge, K. W., & Berkner, K. L. (2013). The Vitamin K Oxidoreductase Is a Multimer That Efficiently Reduces Vitamin K Epoxide to Hydroquinone to Allow Vitamin K-dependent Protein Carboxylation. The Journal of Biological Chemistry, 288(44), 31556–31566.

Tie, J.-K., Jin, D.-Y., Straight, D. L., & Stafford, D. W. (2011). Functional study of the vitamin K cycle in mammalian cells. Blood, 117(10), 2967–2974.

Megan Ware RDN LD. (2015, September 29). “Vitamin K: Health Benefits and Recommended Intake.” Medical News Today. Retrieved from

Ekelund, H., Finnström, O., Gunnarskog, J., Källén, B., & Larsson, Y. (1993). Administration of vitamin K to newborn infants and childhood cancer. BMJ : British Medical Journal, 307(6896), 89–91.

Bruce N. Ames, “Prevention of Mutation, Cancer, and Other Age-Associated Diseases by Optimizing Micronutrient Intake,” Journal of Nucleic Acids, vol. 2010, Article ID 725071, 11 pages, 2010. doi:10.4061/2010/725071

Juanola-Falgarona, M., Salas-Salvadó, J., Estruch, R., Portillo, M. P., Casas, R., Miranda, J., … Bulló, M. (2013). Association between dietary phylloquinone intake and peripheral metabolic risk markers related to insulin resistance and diabetes in elderly subjects at high cardiovascular risk. Cardiovascular Diabetology, 12, 7.

Bentkowski W, Kuzniewski M, Fedak D, et al. Undercarboxylated osteocalcin (Glu-OC) bone metabolism and vascular calcification in hemodialyzed patients. Przegl Lek. 2013;70(9):703-6.

Lamson DW, Plaza SM. The anticancer effects of vitamin K. Altern Med Review. 2003;8(3).

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