What is vitamin K? Do I need both K1 and K2?

Vitamin K may not be as popular and well known as other vitamins and if known at all, it’s for the important role it plays in blood clotting. However, vitamin K is also essential to building strong bones and preventing heart disease.

There are two natural forms of vitamin K. Vitamin K1 (also called phylloquinone) is plentiful in leafy green vegetables, such as kale, collards, spinach and mustard greens, so it’s easy to obtain this vitamin when following a Nutritarian diet.

Vitamin K2 (a few different substances called menaquinones), is produced by microorganisms and scarce in plant foods, so K2 is more difficult to get from a Nutritarian diet. The human body can synthesize some K2 from K1, and intestinal bacteria can produce some K2, but these are very small amounts.5

There is evidence that both vitamin K1 and K2 are important for good health.

Vitamin K is important for:

  1. Blood coagulation
    • Essential for the process of blood clotting. In fact, vitamin K was named for this important function; the scientists who discovered the vitamin named it using the first letter of the German word "koagulation."
  2. Bone health and fracture prevention
    • Vitamin K allows the body to utilize the calcium needed for bone and tooth formation.1, 2 Many studies have associated low vitamin K1 or K2 status with a higher risk of hip fracture or low bone mineral density.2-4
    • Higher intake of vitamin K1 is associated with lower rates of bone loss and fractures, and studies have reported that a causative factor of the low hip fracture incidence in Japan was natto, a fermented soy food, rich in K2.  Following this observation, several studies found supplementation with vitamin K2 to be particularly effective at improving bone health. A review of randomized controlled trials found that vitamin K2 reduced bone loss and reduced the risk of fractures; vertebral fracture by 60 percent, hip fracture by 77 percent and all non-vertebral fractures by 81 percent.3,6
    • In a more recent study on postmenopausal women taking vitamin K2 supplements daily for three years, decreases in bone loss and bone mineral decline, and increased bone strength were found in the vitamin K2 group compared to placebo.7
    • In women who already had osteoporosis, Vitamin K2 supplementation was also shown to reduce the risk of fracture, reduce bone loss, and increase bone mineral density.8
  3. Heart health via interactions with calcium
    • Vitamin K helps prevent calcification of the coronary arteries (arteries that give blood to the heart). A vitamin K-dependent protein binds up calcium to protect the soft tissues – including the arteries – from calcification.2, 9, 10 Vitamin K2 in particular, helps to prevent the artery wall from stiffening and maintaining elasticity. Coronary artery calcification is a predictor of cardiovascular events, as is arterial stiffness.11, 12
    • Higher vitamin K2 intake has been linked with a lower likelihood of coronary calcification (the same association was not found for K1).10 In 2004, the Rotterdam Study revealed that increased dietary intake specifically of vitamin K2 significantly reduced the risk of coronary heart disease by 50 percent as compared to low dietary vitamin K2 intake. In this study, Vitamin K1 had no effect.9
    • Similar results were found in another study conducted in 2009.13 Furthermore, a systematic review of several studies in 2010 also found no association between vitamin K1 intake and coronary heart disease, but higher K2 intake was associated with lower risk.14

It is unclear why vitamin K2 seems to be more beneficial than K1 for the cardiovascular system; it could be due to differences in absorption or biological activity between the vitamin K forms.2,15 Regardless of the reason, the evidence suggests that taking in vitamin K2 in addition to K1 is likely beneficial to help protect against vascular calcification.

Leafy greens for K1, supplements for K2

Ongoing research on vitamin K is revealing new ways that vitamin K acts to maintain good health. There is some evidence that vitamin K is involved in insulin metabolism, and higher intake of vitamins K1 and K2 are associated with lower risk of type 2 diabetes.16,17

Future studies will also help us to understand why K2 appears more protective against blood vessel calcification, and whether there are benefits of vitamin K that are exclusive to either K1 or K2. Leafy green vegetables provide generous amounts of vitamin K1, and getting K2 from a supplement is likely beneficial.

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  1. Kidd PM. Vitamins D and K as pleiotropic nutrients: clinical importance to the skeletal and cardiovascular systems and preliminary evidence for synergy. Altern Med Rev 2010;15:199-222.
  2. Beulens JW, Booth SL, van den Heuvel EG, et al. The role of menaquinones (vitamin K(2)) in human health. Br J Nutr 2013;110:1357-1368.
  3. Feskanich D, Weber P, Willett WC, et al. Vitamin K intake and hip fractures in women: a prospective study. Am J Clin Nutr 1999, 69:74-79.
  4. Tsugawa N, Shiraki M, Suhara Y, et al. Low plasma phylloquinone concentration is associated with high incidence of vertebral fracture in Japanese women. J Bone Miner Metab 2008;26:79-85.
  5. Oregon State University. Linus Pauling Institute. Micronutrient Information Center: Vitamin K [http://lpi.oregonstate.edu/infocenter/vitamins/vitaminK/]
  6. Cockayne S, Adamson J, Lanham-New S, et al. Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Arch Intern Med 2006;166:1256-1261.
  7. Knapen MH, Drummen NE, Smit E, et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int 2013;24:2499-2507.
  8. Vitamin K2. Monograph. Altern Med Rev 2009;14:284-293.
  9. Geleijnse JM, Vermeer C, Grobbee DE, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr 2004;134:3100-3105.
  10. Beulens JW, Bots ML, Atsma F, et al. High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis 2009;203:489-493.
  11. Greenland P, Bonow RO, Brundage BH, et al. ACCF/AHA 2007 clinical expert consensus document on coronary artery calcium scoring by computed tomography in global cardiovascular risk assessment and in evaluation of patients with chest pain: a report of the American College of Cardiology Foundation Clinical Expert Consensus Task Force (ACCF/AHA Writing Committee to Update the 2000 Expert Consensus Document on Electron Beam Computed Tomography) developed in collaboration with the Society of Atherosclerosis Imaging and Prevention and the Society of Cardiovascular Computed Tomography. J Am Coll Cardiol 2007;49:378-402.
  12. Cecelja M, Chowienczyk P. Role of arterial stiffness in cardiovascular disease. JRSM Cardiovasc Dis 2012;1.
  13. Gast GC, de Roos NM, Sluijs I, et al. A high menaquinone intake reduces the incidence of coronary heart disease. Nutrition, metabolism, and cardiovascular diseases: NMCD 2009;19:504-510.
  14. Rees K, Guraewal S, Wong YL, et al. Is vitamin K consumption associated with cardio-metabolic disorders? A systematic review. Maturitas 2010;67:121-128.
  15. Grober U, Reichrath J, Holick MF, Kisters K. Vitamin K: an old vitamin in a new perspective. Dermatoendocrinol 2014, 6:e968490.
  16. Ibarrola-Jurado N, Salas-Salvado J, Martinez-Gonzalez MA, et al. Dietary phylloquinone intake and risk of type 2 diabetes in elderly subjects at high risk of cardiovascular disease. Am J Clin Nutr 2012.
  17. Beulens JW, van der AD, Grobbee DE, et al. Dietary phylloquinone and menaquinones intakes and risk of type 2 diabetes. Diabetes Care 2010;33:1699-1705.