Population-based studies have shown an inverse association between dietary menaquinones (MK-n, vitamin K2) intake, coronary calcification and coronary heart disease risk, suggesting a potential role of vitamin K in vascular health.
Vitamin K serves as a cofactor for γ-glutamate carboxylase, promoting the post-translational conversion of glutamate residues into γ-carboxyglutamate (Gla) in γ-carboxyglutamate-proteins. The γ-carboxyglutamate-residues confer calcium-binding properties needed for the proper functioning of these proteins. The most studied γ-carboxyglutamate-proteins are osteocalcin (synthesised by osteoblasts) and matrix γ-carboxyglutamate-protein (MGP, synthesised primarily by vascular smooth muscle cells).
When vitamin K levels are insufficient, carboxylation proceeds to a lesser extent, resulting in the release of γ-carboxyglutamate-proteins in the circulation as undercarboxylated species. Circulating uncarboxylated osteocalcin and desphospho-uncarboxylated matrix Gla-protein are recognised markers for bone and vascular vitamin K status, respectively. Remarkably, substantial fractions of osteocalcin and matrix Gla-protein circulate as uncarboxylated species in most healthy adults, suggesting that vitamin K insufficiency is widespread in Western society. High levels of uncarboxylated osteocalcin form an independent risk predictor for bone fracture and low bone mineral density. High levels of desphospho-uncarboxylated matrix Gla-protein have been found in people at increased risk for cardiovascular disease and have been associated with arterial calcification and cardiovascular mortality. Osteocalcin and matrix Gla-protein carboxylation can be improved by increased vitamin K intake by diet and supplements.
This study found that consuming a yoghurt drink fortified with low doses of vitamin K (menaquinone-7 (MK-7), daily dose of 56 µg), vitamins C and D, and omega-3 PUFA (EPA + DHA, daily dose of 0.2 g) significantly improved vitamin K status.
Knapen MHJ et al., Yogurt drink fortified with menaquinone-7 improves vitamin K status in a healthy population, J Nutr Sci. 2015; 4: e35.