Vitamin K Intake and Human Health

Dear Colleagues,

All vitamin K (VK) analogs are active as a cofactor for the post-translational formation of Gla-proteins (Clotting factors, osteocalcin (bone Gla-protein), matrix Gla-protein (MGP), and so on). However, of the VK analogs, menaquinone-4 (MK-4) has specific activities for various important physiological functions. Most of the menaquinone analogs (MK-n = vitamin K2) are synthesized by microorganisms, but many researchers have reported that MK-4 is unique in being synthesized by the conversion of orally ingested VK1 or menaquinones (VK2) by endogenous enzymatic action in the major tissues of germfree rats and mice which lack their intestinal microbiota. Therefore, future studies must be undertaken to clarify the important role of MK-4 existence in the tissues, as well as comparative studies using vitamin K1 against MK-4 because orally ingested VK1 (or MK-n) is partially converted into MK-4 in each tissue. Studies on unique functions of MK-4, such as bone formation activity that is dependent or independent on osteocalcin, and the mechanism of anti-cancer, anti-atherosclerosis, anti-diabetes, anti-inflammation activities must be included; furthermore, studies on functions through the binding to the nuclear steroid X receptor (SXR or PXR), and on the direct effect of MK-4 on steroid hormone (testosterone) synthesis in the testis or brain must be added to this issue.

Dr. Michio Komai
Guest Editor

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