Fat-soluble vitamin K comes in two forms. The most common type is phylloquinone (K1), found in green leafy vegetables such as collard greens, kale, and spinach. The other type, menaquinones (K2), is present in smaller amounts in chicken, egg yolks, butter and cheese, and fermented foods. Bacteria in the human body also create menaquinones.[1]
Vitamin K is an essential nutrient that serves several roles in the body. One of its most vital roles is to regulate calcium deposition, preventing calcification in blood vessels and kidneys while promoting it in bones.[2]
Moreover, it aids in creating proteins required for blood clotting and bone formation. Prothrombin, which is directly involved in blood clotting, and osteocalcin, which promotes proper bone tissue formation, are two proteins that are vitamin K dependent.[1]
Besides the bones, vitamin K is present in other body parts such as the liver, brain, heart, pancreas, and bones. As it is rapidly broken down and excreted in urine or stool, toxic levels are rarely reached, even with high intakes.
Calcium buildup in arteries is a significant risk factor for heart disease, but vitamin K may help prevent it. High vitamin K2 consumption is associated with a lower risk of arterial calcification and death from heart disease.[3]
One study found that for every 10 mcg of vitamin K2 consumed daily, the heart disease risk decreased by 9%.[4] In contrast, vitamin K1 seems to be ineffective. However, these findings are from observational studies, and more controlled trials on vitamin K2 and heart disease are needed.[5]
Yet, there is a clear link between vitamin K and heart health and a biological mechanism that supports its efficacy.
Vitamin K2 activates the proteins matrix GLA and osteocalcin, essential in building and maintaining bones.
Controlled studies suggest that K2 may have significant benefits for bone health. In one study, postmenopausal women taking vitamin K2 supplements experienced much slower age-related bone mineral density loss than the ones who did not take supplements.[6]
Other studies in Japanese women found that vitamin K2 reduced spinal fractures by 60%, hip fractures by 77%, and non-spinal fractures by 81%. However, two review studies have inferred that evidence for suggesting vitamin K supplements for this purpose is scarce.[7]
Vitamin K is essential for the production of four out of the 13 proteins needed for blood clotting, which is necessary for stopping bleeding and allowing wound healing. Patients prescribed blood thinners or anticoagulants to prevent blood clots in the heart, lungs, or legs need to be cautious about their vitamin K intake since its blood clotting action has the potential to counteract the effects of blood-thinning medications.
Prothrombin time (PT) is a typical method used to measure blood levels of vitamin K. Individuals taking anticoagulant medications, such as warfarin (Coumadin), may have to maintain a consistent intake of vitamin K through food and supplements. Even if minor changes in vitamin K intake rarely affect PT levels, sudden and significant intake variations can interfere with the effectiveness of the medication.[1]
The minimum effective dose for phylloquinone (vitamin K1) is 50 mcg, which is enough to satisfy the Recommended Daily Intake (RDI) for vitamin K; the maximum dosage for vitamin K1 is 10,000 mcg (10 mg).
There are different vitamers within the vitamin K2 class, named MK-x. The minimum effective dose for short-chain menaquinones (MK-4) is 1,500 mcg (up to 45 mg doses (45,000 mcg) have been safely used in a super-loading dosing protocol); the minimum effective dose for longer-chain menaquinones (MK-7, MK-8, and MK-9) is between 90 and 360 mcg. Further research is needed to define the maximum effective dose for MK-7.
Vitamin K should be supplemented alongside fatty acids, even if it comes from a plant-based source, so consider taking vitamin K at mealtime. Microwaving plant-based sources of vitamin K will improve its absorption rate.[8]
While rare in adults, a deficiency in vitamin K may occur due to certain medications, like antibiotics, or conditions that impair nutrient absorption. Additionally, infants may become deficient since vitamin K cannot pass through the placenta, and breast milk contains low vitamin K levels.
Without sufficient blood clotting proteins at birth, there is an increased risk of bleeding if they do not take vitamin K supplements. The most typical signs of a deficiency include prolonged blood clotting time, bleeding, hemorrhaging, and the development of osteopenia or osteoporosis
Vitamin K is unlikely to cause harm. There have been no reports of harmful effects from consuming too much vitamin K from food or supplements. However, vitamin K can interact with certain medications, and others can affect the body's vitamin K levels.
Warfarin and similar anticoagulants can reduce the activity of vitamin K, which can affect blood clotting. People taking these medications should keep their vitamin K intake consistent to avoid unexpected changes in anticoagulant effects.
Bile acid sequestrants and the weight loss drug orlistat can decrease vitamin K and other fat-soluble vitamin absorption, but the clinical significance of this effect is unclear. Those who use these medications for an extended period should have their vitamin K status checked.[1]
1. Office of Dietary Supplements. (2021, March 29). Vitamin K - Health Professional Fact Sheet. National Institutes of Health. Retrieved March 20, 2023, from https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
2. Theuwissen, E., Smit, E., & Vermeer, C. (2012). The role of vitamin K in soft-tissue calcification. Advances in nutrition (Bethesda, Md.), 3(2), 166–173. https://doi.org/10.3945/an.111.001628
3. Anderson, Kruszka, Delaney, He, Burke, Alonso, Bild, Budoff, & Michos. (2016, October 11). Calcium Intake From Diet and Supplements and the Risk of Coronary Artery Calcification and its Progression Among Older Adults: 10‐Year Follow‐up of the Multi‐Ethnic Study of Atherosclerosis (MESA). Journal of the American Heart Association. Retrieved March 20, 2023, from https://www.ahajournals.org/doi/10.1161/JAHA.116.003815#
4. Gast, G. C., de Roos, N. M., Sluijs, I., Bots, M. L., Beulens, J. W., Geleijnse, J. M., Witteman, J. C., Grobbee, D. E., Peeters, P. H., & van der Schouw, Y. T. (2009). A high menaquinone intake reduces the incidence of coronary heart disease. Nutrition, metabolism, and cardiovascular diseases : NMCD, 19(7), 504–510. https://doi.org/10.1016/j.numecd.2008.10.004
5. Shea, M. K., & Holden, R. M. (2012). Vitamin K status and vascular calcification: evidence from observational and clinical studies. Advances in nutrition (Bethesda, Md.), 3(2), 158–165. https://doi.org/10.3945/an.111.001644
6. Knapen, M.H.J., Drummen, N.E., Smit, E. et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int 24, 2499–2507 (2013). https://doi.org/10.1007/s00198-013-2325-6
7. Cockayne, S., Adamson, J., Lanham-New, S., Shearer, M. J., Gilbody, S., & Torgerson, D. J. (2006). Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Archives of internal medicine, 166(12), 1256–1261. https://doi.org/10.1001/archinte.166.12.1256
8. Patel, K. (2022, September 28). Vitamin K Health benefits, dosage, safety, side-effects, and more. Examine. Retrieved March 22, 2023, from https://examine.com/supplements/vitamin-k/
