Menaquinones, bacteria, and the food supply: the relevance of dairy and fermented food products to vitamin K requirements.

Vitamin K exists in the food supply as phylloquinone, a plant-based form and as menaquinones (MKs), a collection of isoprenologues mostly originating from bacterial synthesis. Although multiple bacterial species used as starter cultures for food fermentations synthesize MK, relatively little is known about the presence and distribution of MK in the food supply and the relative contribution of MK to total dietary vitamin K intake. Dairy products may be a predominant source of dietary MK in many regions of the world, and there is recent interest in enhancing the MK content of dairy products through identification and selection of MK-producing bacteria in dairy fermentations. This interest is increased by emerging evidence that current dietary recommendations based on the classic role of vitamin K as an enzyme cofactor for coagulation proteins may not be optimal for supporting vitamin K requirements in extrahepatic tissues and that MK may have unique bioactivity beyond that as an enzyme cofactor. Observational studies have reported favorable associations between MK intake and bone and cardiovascular health. Although randomized trials have provided some evidence to support the beneficial effects of MK on bone, the evidence to date is not definitive, and randomized trials have not yet examined MK intake in relation to cardiovascular outcomes. Food production practices provide a means to enhance dietary MK availability and intake. However, parallel research is needed to optimize these production practices, develop comprehensive food MK content databases, and test hypotheses of unique beneficial physiological roles of MK beyond that achieved by phylloquinone.