Vitamin K: The multiple faces of an old vitamin

Abstract

Introduction and aim: Recently vitamin K has received much attention because of his newly recognized effects unrelated to haemostasis. It was the aim of the present review to make a survey of the literature during the last decade, concerning the emerging role of vitamin K in regulation of variety of physiological processes. Materials and methods: We performed a search of PubMed database using the following key words: vitamin K, menaquinone, phylloquinone, osteocalcin, matrix gla-protein, vascular calcification, bone metabolism, diabetes, neurodegenerative diseases, cancer. Results: Most of the effects of interest are mediated through vitaminK-dependent proteins, such as osteocalcin (OC), matrix-gla protein (MGP), Gas6, protein S. However, in the brain, it is involved in the regulation of the sphingolipid metabolism also by directly affecting the activity of different enzymes. In cardiovascular research, MGP appears to be one of the major inhibitors of vascular calcification. At the same time, OC has long been considered a protein specific to osteolblasts and important for their functions. Subclinical deficiency of vitamin K is relatively common, especially in elderly, possibly contributing to bone demineralization and vascular calcification. Thus, the `calcium paradox` of older age may turn out to be manageable by adequate substitution with this vitamin. An exciting research, indirectly linked to vitamin K itself, is related to OC as a key factor in the suggested regulatory loop between the bone and the pancreas. Experimental evidence shows that osteoblasts-derived OC acts as a hormone to induce insulin secretion, improve insulin sensitivity and enhance glucose uptake.