Vitamin K Overview

Vitamin K plays a major role in the body's blood clotting system. There are three forms of vitamin K: K 1 (phylloquinone), found in plants; K 2 (menaquinone), produced by bacteria in your intestines; and K 3 (menadione), a synthetic form.

Vitamin K is used medically to reverse the effects of "blood-thinning" drugs, such as warfarin (Coumadin). Growing evidence suggests that it may also be helpful for osteoporosis.

Vitamin K is an essential nutrient, but you need only a tiny amount of it. The official U.S. recommendations for daily intake have been set as follows:

• Infants

• 0-6 months: 2 mcg

• 7-12 months: 2.5 mcg

• Children

• 1-3 years: 30 mcg

• 4-8 years: 55 mcg

• Males

• 9-13 years: 60 mcg

• 14-18 years: 75 mcg

• 19 years and older: 120 mcg

• Females

• 9-13 years: 60 mcg

• 14-18 years: 75 mcg

• 19 years and older: 90 mcg

• Pregnant Women

• 18 years or younger: 75 mcg

• 19 years and older: 90 mcg, preferably the K 1 variety (phylloquinone)

• Nursing Women

• 18 years or younger: 75 mcg

• 19 years and older: 90 mcg, preferably the K 1 variety (phylloquinone)

Vitamin K (in the form of K 1 ) is found in green leafy vegetables. Kale and turnip greens are the best food sources, providing about 10 times the daily adult requirement in a single serving. Spinach, broccoli, lettuce, and cabbage are very rich sources as well, and you can get perfectly respectable amounts of vitamin K in such common foods as oats, green peas, whole wheat, and green beans, as well as watercress and asparagus.

Vitamin K (in the form of K 2 ) is also manufactured by bacteria in the intestines and is a major source of vitamin K. Long-term use of antibiotics can cause a vitamin K deficiency by killing these bacteria. However, this effect seems to be significant only in people who are deficient in vitamin K to begin with. ^{1 2 3} Pregnant and postmenopausal women are also sometimes deficient in this vitamin. ^{4 5} In addition, children born to women taking anticonvulsants while pregnant may be significantly deficient in vitamin K, causing them to have bleeding problems and facial bone abnormalities. ^{6 7} Vitamin K supplementation during pregnancy may be helpful for preventing this.

The blood-thinning drug warfarin (Coumadin) works by antagonizing the effects of vitamin K. Conversely, vitamin K supplements, or intake of foods containing high levels of vitamin K, block the action of this medication and can be used as an antidote. ⁸

Cephalosporins and possibly other antibiotics may also interfere with vitamin K-dependent blood clotting. ^{9 10 11} However, this interaction seems to be significant only in people who have vitamin K-poor diets.

People with disorders of the digestive tract, such as chronic diarrhea , celiac sprue, ulcerative colitis , or Crohn's disease , may become deficient in vitamin K. ^{12 13 14} Alcoholism can also lead to vitamin K deficiency. ¹⁵

In one study of osteoporosis described below, vitamin K was taken at the high dose of 1 mg daily, more than 10 times the necessary nutritional intake.

Vitamin K plays a known biochemical role in the formation of bone. This has led researchers to look for relationships between vitamin K intake and osteoporosis.

Observational studies have found that people with osteoporosis often have low levels of vitamin K, ^{16 17 18} and that people with higher intake of vitamin K have a lower incidence of osteoporosis. ¹⁹ Research also suggests that supplemental vitamin K can reduce the amount of calcium lost in the urine. ^{20 21} This is indirect evidence of a beneficial effect on bone.

However, while these studies are interesting, only double-blind, placebo-controlled trials can actually prove a treatment effective. (For the reasons why, see Why Does This Database Rely on Double-blind Studies? ). Several such studies have been performed on vitamin K for osteoporosis, with generally positive results. ²² One of these was a 3-year, double-blind, placebo-controlled trial of 181 women; it found that vitamin K significantly enhanced the effectiveness of supplementation with calcium , vitamin D , and magnesium . ²³ Participants, postmenopausal women between the ages of 50 and 60, were divided into three groups: receiving either placebo, calcium plus vitamin D plus magnesium, or calcium plus vitamin D plus magnesium plus vitamin K 1 (at the high dose of 1 mg daily). Researchers monitored bone loss by using a standard DEXA bone density scan. The results showed that the study participants using vitamin K along with the other nutrients lost less bone than those in the other two groups.

Benefits were seen in other studies as well. ²⁴ However, another placebo-controlled trial involving 452 older men and woman with normal levels of calcium and vitamin D failed to demonstrate any beneficial effects of 500 mcg per day of vitamin K supplementation on bone density and other measures of bone health over a3-year period. ²⁵ If there is a favorable effect, it is appears to be quite modest. Vitamin K may show its influence most strongly when, instead of DEXA scan alone, more complex tests of bone strength are used. ²⁶ Some evidence hints that vitamin K works by reducing bone breakdown, rather than by enhancing bone formation. ²⁷ For more information, see the Osteoporosis article.

1. Cohen H, Scott SD, Mackie IJ, et al. The development of hypoprothrombinaemia following antibiotic therapy in malnourished patients with low serum vitamin K 1 levels. Br J Haematol. 1988;68:63-66.
2. Conly J, Stein K. Reduction of vitamin K 2 concentrations in human liver associated with the use of broad spectrum antimicrobials. Clin Invest Med. 1994;17:531-539.
3. Shearer MJ, Bechtold H, Andrassy K, Koderisch J, McCarthy PT, Trenk D, Jähnchen E, Ritz E. Mechanism of cephalosporin-induced hypoprothrombinemia: relation to cephalosporin side chain, vitamin K metabolism, and vitamin K status. J Clin Pharmacol. 28(1):88-95.
4. Family Practice News. 1984;14:27.
5. Bloch CA, Rothberg AD, Bradlow BA. Mother-infant prothrombin precursor status at birth. J Pediatr Gastroenterol Nutr. 3(1):101-3.
6. Cornelissen M, Steegers-Theunissen R, Kollée L, Eskes T, Vogels-Mentink G, Motohara K, De Abreu R, Monnens L. Increased incidence of neonatal vitamin K deficiency resulting from maternal anticonvulsant therapy. Am J Obstet Gynecol. 168(3 Pt 1):923-8.
7. Howe AM, Lipson AH, Sheffield LJ, Haan EA, Halliday JL, Jenson F, David DJ, Webster WS. Prenatal exposure to phenytoin, facial development, and a possible role for vitamin K. Am J Med Genet. 58(3):238-44.
8. Crowther MA, Donovan D, Harrison L, McGinnis J, Ginsberg J. Low-dose oral vitamin K reliably reverses over-anticoagulation due to warfarin. Thromb Haemost. 79(6):1116-8.
9. Cohen H, Scott SD, Mackie IJ, et al. The development of hypoprothrombinaemia following antibiotic therapy in malnourished patients with low serum vitamin K 1 levels. Br J Haematol. 1988;68:63-66.
10. Shearer MJ, Bechtold H, Andrassy K, Koderisch J, McCarthy PT, Trenk D, Jähnchen E, Ritz E. Mechanism of cephalosporin-induced hypoprothrombinemia: relation to cephalosporin side chain, vitamin K metabolism, and vitamin K status. J Clin Pharmacol. 28(1):88-95.
11. Goss TF, Walawander CA, Grasela TH Jr, Meisel S, Katona B, Jaynes K. Prospective evaluation of risk factors for antibiotic-associated bleeding in critically ill patients. Pharmacotherapy. 12(4):283-91.
12. Avery RA, Duncan WE, Alving BM. Severe vitamin K deficiency induced by occult celiac disease BR96-026. Am J Hematol. 53(1):55.
13. Benitez L, Hernandez Hernandez L, Sanchez Arcos E, et al. Changes in the prothrombin complex as clinical manifestation of celiac sprue in adults. Rev Clin Esp. 1996;196:492-493.
14. Krasinski SD, Russell RM, Furie BC, Kruger SF, Jacques PF, Furie B. The prevalence of vitamin K deficiency in chronic gastrointestinal disorders. Am J Clin Nutr. 41(3):639-43.
15. Iber FL, Shamszad M, Miller PA, Jacob R. Vitamin K deficiency in chronic alcoholic males. Alcohol Clin Exp Res. 10(6):679-81.
16. Kanai T, Takagi T, Masuhiro K, Nakamura M, Iwata M, Saji F. Serum vitamin K level and bone mineral density in post-menopausal women. Int J Gynaecol Obstet. 56(1):25-30.
17. Hart JP, Shearer MJ, Klenerman L, Catterall A, Reeve J, Sambrook PN, Dodds RA, Bitensky L, Chayen J. Electrochemical detection of depressed circulating levels of vitamin K1 in osteoporosis. J Clin Endocrinol Metab. 60(6):1268-9.
18. Bitensky L, Hart JP, Catterall A, Hodges SJ, Pilkington MJ, Chayen J. Circulating vitamin K levels in patients with fractures. J Bone Joint Surg Br. 70(4):663-4.
19. Feskanich D, Weber P, Willett WC, Rockett H, Booth SL, Colditz GA. Vitamin K intake and hip fractures in women: a prospective study. Am J Clin Nutr. 69(1):74-9.
20. Jie KS, Gijsbers BL, Knapen MH, Hamulyák K, Frank HL, Vermeer C. Effects of vitamin K and oral anticoagulants on urinary calcium excretion. Br J Haematol. 83(1):100-4.
21. Knapen MH, Hamulyák K, Vermeer C. The effect of vitamin K supplementation on circulating osteocalcin (bone Gla protein) and urinary calcium excretion. Ann Intern Med. 111(12):1001-5.
22. Braam LA, Knapen MH, Geusens P, Brouns F, Hamulyák K, Gerichhausen MJ, Vermeer C. Vitamin K1 supplementation retards bone loss in postmenopausal women between 50 and 60 years of age. Calcif Tissue Int. 73(1):21-6.
23. Braam LA, Knapen MH, Geusens P, Brouns F, Hamulyák K, Gerichhausen MJ, Vermeer C. Vitamin K1 supplementation retards bone loss in postmenopausal women between 50 and 60 years of age. Calcif Tissue Int. 73(1):21-6.
24. Purwosunu Y, Muharram, Rachman IA, Reksoprodjo S, Sekizawa A. Vitamin K2 treatment for postmenopausal osteoporosis in Indonesia. J Obstet Gynaecol Res. 32(2):230-4.
25. Booth SL, Dallal G, Shea MK, Gundberg C, Peterson JW, Dawson-Hughes B. Effect of vitamin K supplementation on bone loss in elderly men and women. J Clin Endocrinol Metab. 93(4):1217-23.
26. Knapen MH, Schurgers LJ, Vermeer C. Vitamin K2 supplementation improves hip bone geometry and bone strength indices in postmenopausal women. Osteoporos Int. 18(7):963-72.
27. Martini LA, Booth SL, Saltzman E, do Rosário Dias de Oliveira Latorre M, Wood RJ. Dietary phylloquinone depletion and repletion in postmenopausal women: effects on bone and mineral metabolism. Osteoporos Int. 17(6):929-35.