Vitamin K for Cardiovascular Health
By Alan R. Gaby, M.D.
Vitamin K dependent proteins have been found in virtually every tissue in the body. While historically vitamin K has been best known for its capacity to enhance blood clotting, emerging research indicates key roles for bone mineralization, cell function and cardiovascular health.‡
Vitamin K is present in the body and in food in two major forms. Vitamin K1 (also called phylloquinone) is found in plant foods such as leafy green vegetables, and to a lesser extent in some vegetable oils. Vitamin K2 (also called menaquinone) is found in eggs, meat, cheese and natto (fermented soybeans). Vitamin K2 is further classified according to the number of isoprenyl units on its side chain. Thus, vitamin K2 with 4 isoprenyl units is called menaquinone-4 (MK-4), and vitamin K2 with 7 units is called menaquinone-7 (MK-7).
Vitamin K is involved in the synthesis of a protein known as matrix Gla protein, which helps regulate calcium balance in vascular tissue. Vitamin K-dependent proteins also play a role in bone health, programmed cell death, immune function and regulation of cell growth. Studies have shown that the amount of vitamin K needed to optimize some of these functions is greater than the amount needed to promote normal blood clotting function.1 ‡
Research indicates that low vitamin K status can affect vascular calcium balance.2 In a recent observational study of postmenopausal women, higher dietary intake of vitamin K2 was associated with improved calcium balance in the walls of arteries.3 Intake of vitamin K1 did not appear to affect arterial calcium balance. This difference may be due to the fact that vitamin K2 has a higher affinity than vitamin K1 for vascular tissue.‡
Two forms of vitamin K2 that are present in food are also commercially available as supplements. These are MK-4 and MK-7. MK-7, the form of vitamin K2 found in natto, has been found to have greater biological activity and a longer half-life than MK-4. In one study, rats were fed a vitamin K-deficient diet until their prothrombin time became prolonged and they were then given a single dose of vitamin K2, in the form of MK-4 or MK-7. Both types of vitamin K2 shortened the prothrombin time, indicating they were both capable of supporting healthy vitamin K levels. However, the effect lasted only 24 hours in the animals given MK-4 4 5, as compared with at least 72 hours in those given MK-7. Based on these findings, MK-7 may be the preferred form of vitamin K for promoting cardiovascular health.‡
- Berkner KL, Runge KW. The physiology of vitamin K nutriture and vitamin K-dependent protein function in atherosclerosis. J Thromb Haemost 2004;2:2118-2132.
- Spronk HMH, Soute BAM, Schurgers LJ, Thijssen HHW, De Mey JGR, Vermeer C. Tissue-specific utilization of menaquinone-4 results in the prevention of arterial calcification in warfarin-treated rats. J Vasc Res 2003;40:531-537.
- Beulens JW, et al. High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis 2009;203:489-493.
- Matschiner JT, Taggart WV. Bioassay of vitamin K by intracardial injection in deficient adult male rats. J Nutr 1968;94:57-59.
- Sato T, Ohtani Y, Yamada Y, Saitoh S, Harada H. Difference in the metabolism of vitamin K between liver and bone in vitamin K-deficient rats. Br J Nutr 2002;87:307-314.