Kvitamiin

Kvitamin, commonly known as vitamin K, refers to a group of fat-soluble vitamins essential for blood coagulation and bone metabolism. The main natural forms are K1 (phylloquinone), found in green leafy plants, and K2 (menaquinones), produced by gut bacteria and found in some animal products and fermented foods. A synthetic form, K3 (menadione), exists but is not used as a dietary supplement in many countries due to safety concerns.

Biological role and metabolism: Vitamin K acts as a cofactor for the enzyme gamma-glutamyl carboxylase, enabling the gamma-carboxylation of specific glutamate residues on coagulation factors II, VII, IX, and X, as well as anticoagulant proteins C and S. This modification is necessary for their biological activity. Vitamin K also participates in the carboxylation of bone-related proteins such as osteocalcin and matrix Gla protein, linking it to bone health and vascular mineralization. It is absorbed in the small intestine with dietary fat, transported in lipoproteins, and stored mainly in the liver and adipose tissue. The gut microbiota contributes to the body’s vitamin K pool through menaquinones.

Dietary sources and intake: K1 comes from leafy vegetables (e.g., kale, spinach, broccoli), while K2 is abundant in certain fermented foods (notably natto) and some animal products. Oils and dairy also provide K1 and K2. Adequate daily intake varies by age and sex; typical recommendations are about 90 micrograms for adult women and 120 micrograms for adult men.

Deficiency and safety: Vitamin K deficiency is uncommon in healthy adults but can occur with fat malabsorption, long-term antibiotic use, or rare diseases; in newborns, prophylaxis is standard to prevent VKDB. Anticoagulants such as warfarin antagonize vitamin K, requiring stable intake and monitoring. Dietary vitamin K from food is generally safe; high-dose supplements can interfere with anticoagulant therapy.