In Eric Wooltorton's article on vitamin and mineral supplements,1 a footnote to Table 1 states that vitamin K has an anticoagulant effect. In fact, vitamin K promotes healthy coagulation, because it is a cofactor in a carboxylation reaction that is essential for the clotting process.2 [A correction on this point was published previously.3Editor.]
Vitamin K was excluded from this table because it “is not available in Canadian multivitamin preparations.”1 However, vitamin K is included in some multivitamins available in the United States. Given the popularity of cross-border shopping and the availability of products through the Internet, it is possible that many patients of CMAJ readers, or even the journal's readers themselves, are consuming vitamin K in supplement form.
Despite several trials evaluating vitamin K (vitamin K1 [phylloquinone] and vitamin K2 [menatetrenone]) for its effects on bone quality and density4,5,6 and its usefulness in other contexts,7 the toxic effects of even pharmaceutical doses of these 2 naturally occurring forms of vitamin K have not been identified.8 In addition, at least one study, which evaluated the effects of large doses of vitamin K2 (45 mg of menaquinone-4) on hemostatic activation, found no thrombotic tendency at high doses.9
Ruth Wilson Medical Student, Class of 2006 University of Western Ontario London, Ont.
References
- 1.Wooltorton E. Too much of a good thing? Toxic effects of vitamin and mineral supplements. CMAJ 2003;169(1):47-8. [PMC free article] [PubMed]
- 2.Vermeer C, Schurgers LJ. A comprehensive review of vitamin K and vitamin K antagonists. Hematol Oncol Clin North Am 2000;14(2):339-52. [DOI] [PubMed]
- 3.Corrections. CMAJ 2003;169(4):283.
- 4.Iwamoto I, Kosha S, Noguchi S, Murakami M, Fujino T, Douchi T, et al. A longitudinal study of the effect of vitamin K2 on bone mineral density in postmenopausal women: a comparative study with vitamin D3 and estrogen–progestin therapy. Maturitas 1999;31(2):161-4. [DOI] [PubMed]
- 5.Yonemura K, Kimura M, Miyaji T, Hishida A. Short-term effect of vitamin K administration on prednisolone-induced loss of bone mineral density in patients with chronic glomerulonephritis. Calcif Tissue Int 2000;66(2):123-8. [DOI] [PubMed]
- 6.Somekawa Y, Chigughi M, Harada M, Ishibashi T. Use of vitamin K2 (menatetrenone) and 1,25-dihydroxyvitamin D3 in the prevention of bone loss induced by Leuprolide. J Clin Endocrinol Metab 1999;84(8):2700-4. [DOI] [PubMed]
- 7.Takami A, Asakura H, Nakao S. Menatetrenone, a vitamin K2 analog, ameliorates cytopenia in patients with refractory anemia of myelodysplastic syndrome. Ann Hematol 2002;81(1):16-9. [DOI] [PubMed]
- 8.Fairfield KM, Fletcher RH. Vitamins for chronic disease prevention in adults. JAMA 2002; 287(23):3116-26. [DOI] [PubMed]
- 9.Asakura H, Myou S, Ontachi Y, Mizutani T, Kato M, Saito M, et al. Vitamin K administration to elderly patients with osteoporosis induces no hemostatic activation, even in those with suspected vitamin K deficiency. Osteoporos Int 2001; 12 (12):996-1000. [DOI] [PubMed]