Vitamin K: an old vitamin in a new perspective

Abstract

The topic of "Vitamin K" is currently booming on the health products market. Vitamin K is known to be important for blood coagulation. Current research increasingly indicates that the antihaemorrhagic vitamin has a considerable benefit in the prevention and treatment of bone and vascular disease. Vitamin K1 (phylloquinone) is more abundant in foods but less bioactive than the vitamin K2 menaquinones (especially MK-7, menaquinone-7). Vitamin K compounds undergo oxidation-reduction cycling within the endoplasmic reticulum membrane, donating electrons to activate specific proteins via enzymatic gamma-carboxylation of glutamate groups before being enzymatically reduced. Along with coagulation factors (II, VII, IX, X, and prothrombin), protein C and protein S, osteocalcin (OC), matrix Gla protein (MGP), periostin, Gas6, and other vitamin K-dependent (VKD) proteins support calcium homeostasis, inhibit vessel wall calcification, support endothelial integrity, facilitate bone mineralization, are involved in tissue renewal and cell growth control, and have numerous other effects. The following review describes the history of vitamin K, the physiological significance of the K vitamers, updates skeletal and cardiovascular benefits and important interactions with drugs.

Keywords: bone health; cardiovascular health; matrix GLA protein; menaquinone-7; osteocalcin; phylloquinone; vitamin K.

Figure 1.

In the vitamin K cycle, vitamin K-dependent gamma-carboxyglutamic acid (Gla) proteins are carboxylated and activated.

Figure 2.

Structural formulae of biologically active K vitamers.

Figure 3.

Effect of vitamin K on bone and vascular health.

Figure 4.

Comparison of oral bioavailability of vitamin K1 and MK-7: vitamin K serum levels following a single dose of 1 mg vitamin K1 or 1 mg MK-7.

Figure 5.

Carboxylation of osteocalcin by vitamin K1 and MK-7: Vitamin K1 or MK-7 were supplemented daily at a dose of 0.22 μmol in the form of tablets or capsules. Initially, the ratio between carboxylated (cOC) and uncarboxylated osteocalcin (ucOC) was 1.74 in the MK-7 group, 1.8 in the vitamin K1 group and 1.7 in the placebo group. In the placebo group, only vitamin K1 was determined. After approximately 3 days, vitamin K1 and MK-7 increased the carboxylation of osteocalcin, but only the intake of MK-7 led to a further increase in the degree of carboxylation.