OKKKAYYY!!! (Lil’ Jon voice)… lets discuss vitamin K.

Key Concepts

  • Two forms of natural vitamin K – K1 (Phylloquinone) (plants) & K2 (menaquinones) (fermented foods)
  • K2 (MK-7) most biologically active form
  • Food Sources – K1 (green leafy and cruciferous veggies); K2 – Natto (fermented soy, chickpeas, black beans)!
  • Important for blood clotting, bone health, vasculature, preventing mineralization in blood vessels, regulating many cellular functions
  • Directly affects blood thinning medications – supplementation can be dangerous here
  • No known toxicity – not stored readily in body
  • Supplement Vitamin K2 MK-7 seems warranted

Vitamin K Forms

  • K1 – Phylloquinone – produced by plants – natural form
  • K2 – Menaquinone (MK) – commonly found in fermented foods – natural form
    • Vitamers – MK-4 and MK-7 most common
  • K3 – Menadione; synthetic

Vitamin K2 Bacterial Production

A few strains of gut bacteria which normally colonize the colon can synthesize vitamin K2. Their contribution to vitamin K status remain unclear.

Adequate Intakes for Vitamin K

Newborns are at risk for vitamin K deficiency bleeding (VKDB) because they are born sterile (do not have gut microflora to make vitamin K), their is low placental transfer of Vitamin K, low clotting factor levels in newborns, and low Vitamin K transfer in breast milk. Because of this, the American Academy of Pediatrics (AAP) recommends the administration of a single, intramuscular dose of 0.5 to 1 milligram (mg) vitamin K1 at birth. This is considered standard of care. There is a low incidence of VKBD but when it does occur the mortality rate is high. This is why the AAP recommends the vitamin K shot at birth.

Adequate intakes (AI) of vitamin K are dependent upon age and sex. In adult males, AI is 120 mcg/day for males and 90 mcg/day for females. Other age groups can be viewed here.

Although vitamin K is a fat-soluble vitamin, its storage capacity is limited. The body even has a mechanism which recycles vitamin K so that it can be used multiple times.

Vitamin K Food Sources

K1 Food Sources

  • Collards, frozen, boiled, ½ cup – 662% Daily Value (DV)
  • Turnip greens, frozen, boiled ½ cup – 532% DV
  • Spinach, raw, 1 cup – 181% DV
  • Kale, raw, 1 cup – 141% DV
  • Broccoli, chopped, boiled, ½ cup – 138% DV
  • Pumpkin, canned, ½ cup – 25% DV
  • Blueberries, raw, ½ cup – 18% DV
  • Olive oil, 1 tablespoon – 10%

K2 Food Sources

  • Natto (Fermented Soy), 3 ounces (as MK-7, small amount of MK-8) – 1,062% DV
  • Chicken, breast, rotisserie, 3 ounces (as MK-4) – 17% DV
  • Egg, hard boiled, 1 large (as MK-4) – 5%
  • Ground beef, broiled, 3 ounces (as MK-4) – 8%
  • Cheddar cheese, 1½ ounces (as MK-4) – 5%


The absorption of vitamin K1 in its free form is about 80%. In plant form it is tightly bound to chloroplasts and far less bioavailable than in the form of oil or supplements. For instance, the body absorbs only 4% to 17% as much vitamin K1 from spinach as from a tablet. Consuming fat at the same time as vegetables helps to improve vitamin K1 absorption as it is a fat-soluble vitamin. Vitamin K2 appears to be better absorbed than vitamin K1 and remains in the blood 7-8 times longer than vitamin K1 (it has a longer half-life). Vitamers of vitamin K2 with longer side chains appear to be more bioavailable than those with shorter side-chains (e.g. MK-7 is more bioavailable than MK-4). MK-7 appears to be the most biologically active of all forms and vitamers of vitamin K.

Vitamin K Functions

Vitamin K is essential in blood clotting, maintenance of bone health, maintaining blood vessel elasticity, preventing mineralization in blood vessels, and in regulating a host of cellular functions (phagocytosis, cell adhesion, cell proliferation, protection against apoptosis, platelet signaling and vascular hemostasis).

Vitamin K2, specifically the MK-7 vitamer, activates matrix Gla protein (MGP). MGP is a potent inhibitor of calcification – it repels calcium from depositing in the blood vessels and arteries. MGP returns this calcium to the bloodstream and shuttles it to the tissues and bones. Hence, vitamin K2 (MK-7) helps you form strong bones and prevent health complications like kidney stones, heart attacks, and strokes. Vitamin K1 can also serve in this result so long as adequate vitamin K1 levels are present. K1 readily goes to the  liver to activate proteins involved in blood clotting. This role is essential for life because if we got cut and our blood did not clot, we would bleed out and die. Once vitamin K1 fulfills this short-term survival role it can satisfy the roles more essential for longevity, roles fulfilled by K2.

Synthesis of osteocalcin is dependent on adequate amounts of vitamin K. Osteocalcin plays a role in bone mineralization and calcium ion homeostasis – it is required to form strong bones and teeth and to prevent bone loss.

Vitamin K’s Interactions with Other Vitamins and Drugs

Large doses of vitamin A appear to interfere with vitamin K absorption while large doses of vitamin E appear to interfere with normal blood clotting. 1,000 IU/day of vitamin E for 12 weeks decreased a vitamin K dependent protein responsible for normal blood clotting.

The blood-thinning (anti-coagulant) effect of medications such as warfarin may be compromised by very high dietary or supplemental vitamin K intake. Up to 100 mcg of vitamin K1 are considered safe for patients taking warfarin, but supplemental doses of 10 to 20 mcg of vitamin K2 (MK-7) can render blood-thinners ineffective.


There is currently no known toxicity for all forms of vitamin K1 and K2.


Vitamin K deficiency is associated with reduced clotting time, easy bruising and easy bleeding, hemorrhagic disease, and osteoporosis.


It seems that vitamin K1 is pretty easy to obtain from the diet, but vitamin K2 really is not, unless you are eating natto. It is still unclear how much vitamin K we actually need in our diet, indicated by the setting of an “Adequate Intake” rather than a Recommended Dietary Allowance (RDA). Adequate intakes are established when evidence is insufficient to develop an RDA; intake at this level is assumed to ensure nutritional adequacy.

What does appear clear is that we are not great at storing vitamin K in the body and that high doses appear safe. Therefore, a supplementation appears warranted considering the crucial roles vitamin K places for overall health. Here is a source that is free of GMO soy and derived from chickpea-natto: Vitamin K2 MK-7.


There is still a lot to learn about vitamin K! I want to do a bit more research on how to make natto and to find a supplement that is a bit more cost effective but does not contain soy. If you can help shoot me a comment, thank you!




  1. How to Make Natto – make sure you do it with Organic, Non-GMO soybeans – most conventional soybeans are genetically-modified
  2. Black Bean Natto
  3. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7
  4. Vitamin K bacterial production
  5. https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/#en18
  6. http://lpi.oregonstate.edu/mic/vitamins/vitamin-K#vitamin-K-oxidation-reduction-cycle
  7. https://articles.mercola.com/sites/articles/archive/2017/01/02/what-are-the-benefits-of-vitamin-k2.aspx
  8. https://www.foundmyfitness.com/vitamin-d

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