Vitamin K is a lesser-known vitamin essential to humans. It is used to describe a group of fat-soluble vitamins that are essential cofactors to make proteins involved in coagulation and calcium balance. Vitamin K1 and K2 are the most important and well-studied forms.
Vitamin K is known as the blood-clotting vitamin and is stored in the liver and other body tissues, including the brain, heart, pancreas, and bone. It plays an important role not only in blood clotting but also in the regulation of the mineralization of bones and cartilage, helping bones grow the way they should. For optimal bone and vascular health, relatively high intakes of vitamin K are required. Deficiency has been linked to vascular calcification and osteoporosis.1
Healthy adults generally get enough vitamin K from their diet. Low levels can result in a risk of uncontrolled bleeding. Deficiency is seen most often in newborns, where prophylactic vitamin K is recommended to prevent the risk of uncontrolled bleeding.2
Vitamin K is found naturally in green leafy vegetables, such as kale, spinach, turnip greens, collards, Swiss chard, mustard greens, parsley, romaine, and green leaf lettuce as well as vegetables such as Brussels sprouts, broccoli, cauliflower, and cabbage. Fish, liver, meat, eggs, and cereals contain smaller amounts. Other foods high in vitamin K include sun-dried tomatoes, celery, scallions, blackberries, raspberries, dried sage, dried basil, okra, pickles, prunes, chili powder, asparagus, carrots, cucumbers, yogurt, and kefir.
Things that interfere with Vitamin K absorption:
- Antibiotic use greater than 10 days
- Low fat diet and fat-blocking supplements
- Bile acid medications called sequestrants to lower LDL cholesterol and prevent fat absorption such as cholestyramine, colestipol, or colesevelam
- Fat substitutes or blockers such as Orlistat, Xenical, and Olestra.
- Mineral oil consumption
- GI tract diseases (such as Celiac or Crohn’s Disease), liver diseases, and estrogen drugs
- Heavy alcohol use
- Preservative butylated hydroxytoluene (BHT)
- Dilantin use
How supplementation with Vitamin K2 may be helpful:
- Vitamin K2 may be helpful in the managing diabetes, cancer, and osteoarthritis.
- Observational studies suggest that diets low in vitamin K are associated with increased risk of fractures and osteoarthritis in older adults. Studies have provided some conflicting evidence and are inconclusive. as to whether supplementation reduces fracture risk.3
- Improves bone quality, reducing likelihood of fractures according to observational studies. However, randomized controlled trials of vitamin K supplementation in Caucasian populations have not shown clinically significant improvements in bone mineral density and there is not enough current evidence to recommend the routine use of supplementation for the prevention of bone loss, fractures, or osteoarthritis in postmenopausal Caucasian women.4
- Vitamin K antagonists have been shown to increase the risk for osteoporosis and osteoarthritis (OA). Although the current research data have not established the optimal doses to prevent OA, ensuring sufficient dietary intake seems to protect the elderly from OA.5
- Vitamin K has been reported to influence glucose metabolism. It plays an important role in the prevention and control of type 2 diabetes, which may be related to the improvement of insulin metabolism and blood glucose level.6 As such, it impacts diabetes and its associated complications.7
- A review of studies of the effects of supplementation on cardiovascular health highlight the lack of evidence to determine the effectiveness of vitamin K supplementation for the primary prevention of cardiovascular disease and support the need for further studies.8
Types of Vitamin K
- K1 (phylloquinone) is made by plants, so found in food. It is better absorbed in consumption with fat. Some animal sources can convert K1 to K2.
- K2 (menaquinone) is involved in calcium transport, preventing calcium deposition in blood vessel walls and helps to improve bone density.1
- K2 in the form of MK-7 (menaquinone-7) from fermented soybeans stimulates osteoblasts to promote bone growth and inhibits osteoclasts that result in bone demineralization. It has a longer half-life and has become more of the recommended standard. It is derived from natto (fermented soy) and can be found in some fermented foods and cheese. It is available as a supplement. In Japanese studies, it has been used extensively, with a systematic review of studies showing significant reduction of hip fractures, vertebral fractures and non-vertebral fractures. 9
- K2 in the form of MK-4 (menaquinone-4) can be found naturally in butter, eggs, and lard. It can be synthesized in the gut by bacteria, however, very little is absorbed. It available as a supplement.
How to take vitamin K
- Taking vitamin K with fat helps improve absorption, as vitamin K is a fat-soluble vitamin.
- Vitamin K2 in the form of MK-7 is available as a supplement usually with a dose of 100–120𝜇gm.
- Vitamin D3 with K2 together as an approach to osteoporosis treatment may significantly reduce risk of disease and death. In menopausal females, combination of vitamin K and vitamin D appears to be effective in osteoporosis, although long-term larger studies are needed to confirm current observations.10 Vitamin K is approved for treatment of osteoporosis in Japan.
When to be careful with taking vitamin K:
- Vitamin K2 (MK-4) supplementation is safe and does not cause excessive blood clotting even at doses of 15 mg three times a day.11 However, supplementation with MK-7 can interfere with anticoagulation therapy (ie., warfarin) when used above 50𝜇gm/day.12 Interestingly, when supplementing with anticoagulation therapy, adjusting anti-coagulation may be less needed, although studies have been small with insufficient information.13 A small amount of K2 while on anti-coagulation therapy may reduce the risk of osteoporosis, osteoarthritis, and vascular and tissue calcification. Supplementation with newer agents that are non-K pathway dependent can also be used when supplementing with K2.
- While no toxicity is found with higher doses of K1 or K2 in oral form, upper limits do need to be established. Toxicity has been found in IV form in high doses and may be due to the preparation.
There is a lot of anecdotal and observational data to support the important role of vitamin K in disease prevention. While there is conflicting evidence around the exact role of vitamin K and its specific supplementation in diseases of inflammation, there is evidence to support that it likely plays an important role.14 A diet rich in vitamin K in healthy individuals can provide adequate amounts. For some individuals, however, supplementation may be indicated and is usually safe.
1. Flore R, Ponziani FR, di Rienzo TA, et al. Something more to say about calcium homeostasis: the role of vitamin K2 in vascular calcification and osteoporosis. European review for medical and pharmacological sciences. 2013;17(18).
2. Jullien S. Vitamin K prophylaxis in newborns. BMC pediatrics. 2021;21(Suppl 1):350. doi:10.1186/s12887-021-02701-4
3. Tsugawa N, Shiraki M. Vitamin K nutrition and bone health. Nutrients. 2020;12(7). doi:10.3390/nu12071909
4. Hamidi MS, Cheung AM. Vitamin K and musculoskeletal health in postmenopausal women. Molecular Nutrition and Food Research. 2014;58(8). doi:10.1002/mnfr.201300950
5. Chin KY. The relationship between vitamin k and osteoarthritis: A review of current evidence. Nutrients. 2020;12(5). doi:10.3390/nu12051208
6. Cao AL, Lai YW, Chen HG, Sheng LT, Pan A. Research progress of relationship between vitamin K and type 2 diabetes. Zhonghua yu fang yi xue za zhi [Chinese journal of preventive medicine]. 2020;54(5). doi:10.3760/cma.j.cn112150-20190520-00407
7. Ho HJ, Komai M, Shirakawa H. Beneficial effects of vitamin k status on glycemic regulation and diabetes mellitus: A mini-review. Nutrients. 2020;12(8). doi:10.3390/nu12082485
8. Hartley L, Clar C, Ghannam O, Flowers N, Stranges S, Rees K. Vitamin K for the primary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews. Published online September 21, 2015. doi:10.1002/14651858.CD011148.pub2
9. Cockayne S, Adamson J, Lanham-New S, Shearer MJ, Gilbody S, Torgerson DJ. Vitamin K and the prevention of fractures: Systematic review and meta-analysis of randomized controlled trials. Archives of Internal Medicine. 2006;166(12). doi:10.1001/archinte.166.12.1256
10. Rosa J, Stančíková M. Effect of Vitamin K on musculoskeletal health in postmenopausal women. Clinical Osteology. 2019;24(1).
11. Asakura H, Myou S, Ontachi Y, et al. Vitamin K administration to elderly patients with osteoporosis induces no hemostatic activation, even in those with suspected vitamin K deficiency. Osteoporosis International. 2001;12(12). doi:10.1007/s001980170007
12. Schurgers LJ, Teunissen KJF, Hamulyák K, Knapen MHJ, Vik H, Vermeer C. Vitamin K-containing dietary supplements: Comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007;109(8). doi:10.1182/blood-2006-08-040709
13. Mahtani KR, Heneghan CJ, Nunan D, Roberts NW. Vitamin K for improved anticoagulation control in patients receiving warfarin. Cochrane Database of Systematic Reviews. 2014;2014(5). doi:10.1002/14651858.CD009917.pub2
14. Harshman SG, Shea MK. The Role of Vitamin K in Chronic Aging Diseases: Inflammation, Cardiovascular Disease, and Osteoarthritis. Current Nutrition Reports. 2016;5(2). doi:10.1007/s13668-016-0162-x
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