Vitamin K and Gut Microbiome

Individuals with inflammatory bowel disease (IBD), particularly those with Crohn’s disease, often experience deficiencies in vitamins K and D despite adequate dietary intake, pointing to malabsorption as the culprit. These deficiencies are linked to reduced bone mineral density (BMD), as low circulating levels of vitamin K and D were found to be independent risk factors for poor bone health in this group (Kuwabara et al, 2009). Chronic gut inflammation and impaired intestinal absorption in IBD can compromise the uptake of fat-soluble vitamins essential for bone metabolism, highlighting the importance of gut health in nutrient status and skeletal integrity.

Emerging evidence highlights the potential health roles of bacterially derived forms of vitamin K, known as menaquinones, which may exert anti-inflammatory effects. To explore these possibilities, researchers measured fecal and serum menaquinone levels, gut microbiota composition, and markers of inflammation in 80 adults who consumed either a whole grain-rich or refined grain-based diet over six weeks. Fecal menaquinone levels were highly variable among individuals, and were significantly lower in participants consuming whole grains. Interestingly, individual differences in menaquinone profiles were more strongly linked to gut bacterial composition than to diet alone, with genera such as Bacteroides and Prevotella showing strong associations with specific menaquinone forms. Despite these associations, menaquinones were not detectable in the bloodstream, and their concentrations did not correlate with any inflammatory markers. These findings suggest that while gut microbes produce significant amounts of menaquinones and their profiles reflect microbial composition, the physiological impact of these microbial vitamin K forms on systemic inflammation and health remains unclear (Karl et al., 2017).

Most microbiome-derived metabolites enter the bloodstream near the gut lining and are transported directly to the liver via the portal vein. The liver plays a key regulatory role here, modifying, storing, or releasing these compounds based on the body’s current needs. This modulation applies to vitamin K1, primarily obtained from the diet, and, to a lesser extent, vitamin K2. As a result, even when serum levels of these vitamins appear stable, the liver’s internal handling of them can vary significantly depending on whether the body is in a catabolic (breaking down) or anabolic (building up) state.

Broad-spectrum antibiotics have long been linked to elevated prothrombin time (PT), a measure of how long it takes blood to clot, suggesting that gut bacteria may help maintain normal coagulation by producing vitamin K. A prolonged PT can indicate impaired clotting and increased bleeding risk. Factor VII, one of the first clotting proteins activated in the coagulation cascade, is dependent on vitamin K for proper function. In this study, researchers isolated pure menaquinone (vitamin K2) from Staphylococcus aureus and delivered it directly into the ileum of four healthy volunteers who were placed on a vitamin K–restricted diet and anticoagulated with warfarin—a medication that reduces clotting by inhibiting the recycling of vitamin K. Within 24 hours of ileal K2 delivery, participants showed a significant increase in factor VII levels and a decrease in PT, while no such changes were observed during the control phase (Conly et al., 1994). These findings provide direct evidence that vitamin K2 produced by gut microbes can be absorbed in the distal small intestine and may contribute to vitamin K–dependent blood clotting in humans.

Menaquinones, also known as vitamin K2, are produced by gut bacteria in the lower intestinal tract (Beulens et al., 2013). This fat-soluble vitamin is essential for blood clotting, enabling the liver to produce clotting factors II, VII, IX, and X, which are crucial for stopping bleeding after injuries. While vitamin K is also obtained from food sources, menaquinones are synthesized by the gut microbiota, highlighting the integral role of the microbiome in our vitamin K status.