Vitamin K is a crucial and sometimes forgotten nutrient. Just like vitamins A, D, and E, vitamin K is a fat soluble vitamin.

There are two types of vitamin K: K1 (phylloquinone) and K2 (menaquinone, of which there are actually several types). Vitamin K1 is most important for regulation of blood clotting, while vitamin K2 helps activate proteins and is more important for bone health and for preventing cancer, diabetes, and heart disease.

Sources of Vitamin K1

Major sources of vitamin K1 include leafy green vegetables (e.g. kale, spinach, collard greens, Swiss chard, turnip greens, mustard greens, parsley, romaine lettuce) and cruciferous vegetables (Brussels sprouts, broccoli, cabbage). Asparagus, bok choy, peas, parsley and lentils, as well as some fruits such as prunes, grapes, raspberries, and especially blueberries also contain high amounts of K1.

Sources of Vitamin K2

Vitamin K2 is made by bacteria and found in small amounts in some fermented foods and animal products. There are very few plant-based sources. The exception is foods fermented with those K2 producing bacteria. Natto, a fermented soy product, contains the greatest amount. Other plant-based sources include sauerkraut, tempeh, and kombucha, but their K2 content is inconsistent and will depend on the method of production. Some studies show that K2 is made by human intestinal flora.^[1] Additionally, gut bacteria have the ability to convert vitamin K1 into K2. For example, one study demonstrated that when breastfeeding mothers were supplemented with vitamin K1, vitamin K2 was produced.^[2]

There is some evidence that vitamin K2 consumption is associated with less heart disease and prostate cancer.

The Dietary Reference Intake for vitamin K is 120 micrograms (µg) for men and 90µg for women. A single half cup serving of broccoli contains this amount, whereas spinach and kale contain 3.5 to 5 times this amount. Despite low intakes of fresh vegetables on a national level, most people within the United States consume adequate vitamin K.^[3] There is no adverse effect from eating too much vitamin K. However, if you take medication that affects blood clotting (e.g. Warfarin/Coumadin), talk to your doctor, as vitamin K can interfere with its efficiency. Finally, vitamin K is a fat-soluble vitamin, and dietary fat can significantly increase its absorption from food.^[4] Most sources of vitamin K contain little or no fat, and therefore adding some fat (e.g. from seeds or nuts) to meals containing vitamin K rich foods can help increase absorption.

There is some evidence that vitamin K2 consumption is associated with less heart disease^[5-7] and prostate cancer.^[8] Other evidence suggests that vitamin K2 supplementation may be beneficial for heart health,^[9] improving insulin sensitivity,^[10] and bone health.^[11],^[12] However, there is no evidence that vitamin K2 supplementation is beneficial in the context of a whole food, plant-based diet containing lots of fresh fruits and vegetables. For example, those eating plant-based diets do not have slow blood clotting times compared to omnivores.^[13],^[14] At the same time, it appears that excess vitamin K2 supplementation may have side effects.^[12]

Symptoms of Vitamin K Deficiency

Unless a person has had repeated courses of strong antibiotics or has severe liver or digestive tract issues, gut bacteria should provide plenty of vitamin K2. Because vitamin K1 is found in large amounts in many foods, vitamin K deficiency is very rare^[15] and usually only develops in severe liver disease or malabsorption syndromes (e.g. caused by digestive tract diseases or certain medications). Symptoms of insufficient vitamin K include easy bruising and bleeding (e.g. bloody urine/stools, nosebleeds) as well as difficult menstruation. To check if you have sufficient vitamin K, ask your physician to check your prothrombin time. It is also possible to directly measure the amount of vitamin K from a blood test, but this can be expensive and is not routinely offered.

To conclude, a whole food, plant-based diet will provide large amounts of vitamin K and keep your gut healthy for optimal vitamin K2 synthesis and total vitamin K absorption.

References

1. Conly JM, Stein K, Worobetz L, Rutledge-Harding S. The contribution of vitamin K2 (menaquinones) produced by the intestinal microflora to human nutritional requirements for vitamin K. Am J Gastroenterol. 1994 Jun;89(6):915-23.
2. Thijssen HH, Drittij MJ, Vermeer C, Schoffelen E. Menaquinone-4 in breast milk is derived from dietary phylloquinone. Br J Nutr. 2002 Mar;87(3):219-26.
3. U.S. Department of Agriculture, Agricultural Research Service. What We Eat in America, 2009-2010. 2012.
4. Gijsbers BL, Jie KS, Vermeer C. Effect of food composition on vitamin K absorption in human volunteers. Br J Nutr. 1996 Aug;76(2):223-9.
5. Geleijnse JM, Vermeer C, Grobbee DE, Schurgers LJ, Knapen MH, van der Meer IM, Hofman A, Witteman JC. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004 Nov;134(11):3100-5.
6. Beulens JW, Bots ML, Atsma F, Bartelink ML, Prokop M, Geleijnse JM, Witteman JC, Grobbee DE, van der Schouw YT. High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis. 2009 Apr;203(2):489-93.
7. Gast GC, de Roos NM, Sluijs I, Bots ML, Beulens JW, Geleijnse JM, Witteman JC, Grobbee DE, Peeters PH, van der Schouw YT. A high menaquinone intake reduces the incidence of coronary heart disease. Nutr Metab Cardiovasc Dis. 2009 Sep;19(7):504-10.
8. Nimptsch K, Rohrmann S, Linseisen J. Dietary intake of vitamin K and risk of prostate cancer in the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC-Heidelberg). Am J Clin Nutr. 2008 Apr;87(4):985-92.
9. Knapen MH, Braam LA, Drummen NE, Bekers O, Hoeks AP, Vermeer C. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. A double-blind randomised clinical trial. Thromb Haemost. 2015 May;113(5):1135-44.
10. Choi HJ, Yu J, Choi H, An JH, Kim SW, Park KS, Jang HC, Kim SY, Shin CS. Vitamin K2 supplementation improves insulin sensitivity via osteocalcin metabolism: a placebo-controlled trial. Diabetes Care. 2011 Sep;34(9):e147.
11. Schurgers LJ, Teunissen KJ, Hamulyák K, Knapen MH, Vik H, Vermeer C. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007 Apr 15;109(8):3279-83.
12. Huang ZB, Wan SL, Lu YJ, Ning L, Liu C, Fan SW. Does vitamin K2 play a role in the prevention and treatment of osteoporosis for postmenopausal women: a meta-analysis of randomized controlled trials. Osteoporos Int. 2015 Mar;26(3):1175-86.
13. Sanders TA, Roshanai F. Platelet phospholipid fatty acid composition and function in vegans compared with age- and sex-matched omnivore controls. Eur J Clin Nutr. 1992 Nov;46(11):823-31.
14. Mezzano D, Munoz X, Martinez C, Cuevas A, Panes O, Aranda E, Guasch V, Strobel P, Munoz B, Rodriguez S, Pereira J, Leighton F. Vegetarians and cardiovascular risk factors: hemostasis, inflammatory markers and plasma homocysteine. Thromb Haemost 1999 Jun;81(6):913-7.
15. Institute of Medicine. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: National Academy Press; 2001.