- Vitamin K is a fat-soluble vitamin that exists in two main forms: vitamin K1 (phylloquinone), found primarily in plant foods, and vitamin K2 (menaquinones), produced by bacteria and found in fermented foods and animal products. This essential nutrient is best known for its crucial role in blood clotting, but research continues to uncover its importance in bone health and other physiological processes.
- The primary function of vitamin K is as a cofactor for enzymes that activate proteins involved in blood clotting. These proteins, known as clotting factors, require vitamin K-dependent carboxylation to become functional. Without adequate vitamin K, these clotting factors remain inactive, potentially leading to increased bleeding risk. This is why vitamin K antagonists like warfarin are used as anticoagulant medications.
- Beyond blood clotting, vitamin K plays a vital role in bone metabolism. It activates osteocalcin, a protein that helps bind calcium to bone tissue. Vitamin K2, in particular, appears to be more effective than K1 in promoting bone health. Research suggests that adequate vitamin K intake may help prevent osteoporosis and reduce fracture risk. It also works synergistically with vitamins D and A to maintain proper calcium metabolism and bone mineralization.
- Vitamin K is increasingly recognized for its role in cardiovascular health. It activates matrix Gla protein (MGP), which helps prevent calcium from depositing in blood vessel walls. This function may help reduce arterial calcification and cardiovascular disease risk. Some studies suggest that higher vitamin K2 intake is associated with reduced risk of heart disease.
- The best dietary sources of vitamin K1 include dark green leafy vegetables like kale, collard greens, spinach, and Brussels sprouts. Vitamin K2 is found in fermented foods like natto (fermented soybeans), cheese, and other dairy products, as well as egg yolks and organ meats. Additionally, beneficial bacteria in the gut can produce some vitamin K2, though the contribution to overall vitamin K status is not fully understood.
- Vitamin K deficiency is rare in healthy adults but can occur in certain populations. Newborns are particularly vulnerable, which is why vitamin K shots are routinely given at birth. Other at-risk groups include people with malabsorption disorders, those on long-term antibiotic therapy (which can disrupt gut bacteria), and individuals taking vitamin K antagonist medications. Symptoms of deficiency primarily manifest as bleeding problems.
- The Adequate Intake (AI) for vitamin K varies by age and sex. For adults, it’s approximately 90 micrograms daily for women and 120 micrograms for men. However, optimal intake levels may be higher, particularly for bone and cardiovascular health. Unlike other fat-soluble vitamins, vitamin K does not appear to pose a risk of toxicity from high dietary intake or supplementation, though those on blood-thinning medications need to maintain consistent intake levels.
- Recent research explores vitamin K’s potential roles beyond blood clotting and bone health. Areas of investigation include its effects on insulin sensitivity, inflammation, cognitive function, and cancer prevention. The different forms of vitamin K (particularly K2 subtypes) may have varying effects on health outcomes, leading to increased interest in understanding their specific biological roles.
- Understanding of vitamin K continues to evolve, with mounting evidence suggesting its importance extends well beyond its classical role in blood coagulation. The distinction between K1 and K2, and the various subtypes of K2, has become an important area of research, as these forms may have different bioavailability and biological effects.
