The gut microbiome has an important relationship with certain vitamins and minerals. Some bacteria in the gut depend on vitamin-derived cofactors for metabolism. Certain micronutrients, such as vitamins B12 and D and selenium, zinc, and magnesium, have been shown to influence the composition of the gut microbiome. Other vitamins, including certain forms of vitamins B and K, are synthesized in the gut microbiome.  

Vitamin K exists in two main forms: vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). Vitamin K1 (phylloquinone) is found in leafy green vegetables and is transported to the liver to support the production of coagulation factors. Vitamin K2 (menaquinone) is found in certain animal products and fermented dairy. It is also produced by certain gut microbiota. Vitamin K2 (menaquinone) has several forms, depending on the length of its side chain, which is delineated with MKn, where n can be from 1 to 14.  

Certain gut microbiota can synthesize menaquinones using two different pathways. Species in the Firmicutes, Proteobacteria, and Bacteroides genera have been associated with one or more of the vitamin K synthesis pathways. Studies have shown that Eubacterium lentum produces MK-6, Escherichia coli synthesizes MK-8, and Bacteroides synthesizes MK-10 and MK-11. 

A recently published review by Yan and colleagues explored the potential impact of vitamin K antagonists on the gut microbiome. Current clinical research is not able to definitively identify a mechanism of action regarding the interplay between vitamin K antagonists and the gut microbiome, however, the authors do provide some theories.  

Yan and colleagues discuss the role of short-chain fatty acids (SCFAs) regarding vitamin K antagonists in the gut microbiome. SCFAs are synthesized by certain beneficial bacteria and are important for immune system health, cell proliferation, and oxidative status. Butyrate, a type of SCFA, acts as a fuel for colonocytes, helps protect intestinal mucosa, is a peroxisome proliferator-activated receptor agonist, and helps maintain intestinal homeostasis.  

Butyrate may also help regulate the absorption of vitamin K. It has also been shown to help modulate the absorption of dietary cholesterol through the downregulation of NPC1L1, a protein involved in cholesterol uptake. Laboratory studies have reported an increase in the absorption of phylloquinone in conditions related to the overexpression of NPC1L1. The authors discuss other potential mechanisms of action beyond the scope of this article. More research is needed before conclusions can be made.  

Vitamin K is a fat-soluble vitamin that supports calcium metabolism, bone formation, and cardiovascular health. Certain forms of vitamin K are also synthesized by the gut microbiome. There is still much to gain in future research on this topic; the gut microbiome, SCFAs, and vitamin K may support aspects of gastrointestinal and human health. 

By Colleen Ambrose, ND, MAT