vitamin K
Vitamin K is a fat-soluble micronutrient that occurs mainly as phylloquinone (K1) and menaquinones (K2 forms); it is essential for blood coagulation and plays roles in bone and cardiovascular health. It matters clinically because deficiency causes bleeding and because vitamin K status interacts with anticoagulant drugs (e.g., warfarin). For content strategy, vitamin K is a high-authority topic linking nutrition, clinical guidance, newborn care, drug safety and aging/bone health—an anchor for micronutrient and medical content clusters.
- Chemical forms
- K1 (phylloquinone) and K2 (menaquinones, MK‑4 to MK‑13); MK‑7 has a long half-life (~72 hours)
- Recommended intake (US AI, 2001)
- Adult men 19+ = 120 µg/day; adult women 19+ = 90 µg/day (Adequate Intake values)
- Discovery & Nobel Prize
- Discovered by Henrik Dam in 1929; Henrik Dam and Edward Doisy awarded the Nobel Prize in Physiology or Medicine in 1943
- Newborn prophylaxis
- A single intramuscular dose of vitamin K (commonly 0.5–1 mg) at birth is recommended to prevent vitamin K deficiency bleeding (per major pediatric guidelines)
- Drug interaction
- Vitamin K antagonizes coumarin anticoagulants (warfarin) by affecting the vitamin K cycle and clotting-factor carboxylation
- Safety / toxicity
- No tolerable upper intake level (UL) established by the Institute of Medicine for natural vitamin K; synthetic menadione (K3) is associated with toxicity and is not used as a supplement
Vitamin K chemistry and biological forms
Biochemically, vitamin K is a cofactor for the gamma-glutamyl carboxylase enzyme that converts specific glutamate residues on vitamin K–dependent proteins to gamma-carboxyglutamate (Gla). This post-translational modification is essential for the activity of several clotting factors (II, VII, IX, X) and extrahepatic proteins such as osteocalcin and matrix Gla protein.
The different forms have distinct pharmacokinetics: K1 is rapidly cleared and concentrates in the liver; some K2 forms (notably MK‑7) have longer circulating half-lives and broader tissue distribution, which underpins research interest in K2 for bone and vascular health.
Physiological roles and clinical outcomes
Beyond hemostasis, vitamin K–dependent proteins regulate bone mineralization (osteocalcin) and inhibit vascular calcification (matrix Gla protein). Observational studies link higher vitamin K status or K2 intake with lower arterial calcification and improved bone density, though randomized trial evidence varies by population and form (K1 vs K2).
Clinical deficiency is uncommon in healthy adults because dietary intake and synthesis by gut bacteria usually suffice, but it occurs in newborns (limited placental transfer, sterile gut), people with fat-malabsorption, prolonged antibiotic use, or those on long-term broad-spectrum antibiotics. Management considerations include supplementation, correcting malabsorption, and careful anticoagulant management.
Dietary sources, absorption, and recommended intakes
Nutrition authorities set Adequate Intake (AI) values rather than RDAs for vitamin K in many jurisdictions. In the United States, AI for adult men (19+) is 120 µg/day and for adult women (19+) is 90 µg/day. There is no established Tolerable Upper Intake Level for natural vitamin K forms by the IOM.
For newborns, single-dose prophylaxis (commonly 0.5–1 mg IM) at birth is recommended by pediatric societies to prevent vitamin K deficiency bleeding; oral regimens exist but require multiple doses and adherence. For adults with malabsorption or on anticoagulants, individualized dosing and monitoring are required.
Interactions, contraindications, and clinical management
Clinicians manage this interaction by counseling consistent vitamin K intake, monitoring INR closely if diets change, and using bridging strategies as indicated. For patients on direct oral anticoagulants (DOACs), vitamin K intake has far less direct impact, but underlying bleeding risk and supplement use should still be discussed.
Contraindications: routine high-dose vitamin K supplementation is not advised for people on warfarin without specialist oversight. Synthetic menadione (K3) is not recommended due to hepatotoxicity and hemolytic anemia risk. In pregnancy and lactation, consultation with obstetric care is recommended for supplementation decisions.
How vitamin K fits into content strategy and editorial planning
Topical clusters should cover K1 vs K2 distinctions, dosing guidance for populations (newborns, older adults, people with malabsorption), interactions with anticoagulants, and evidence summaries on bone and heart outcomes. Use data-driven assets—tables of food sources, clinical guideline summaries, and comparison charts—to capture both informational and transactional intents (e.g., supplement reviews).
Because vitamin K has safety and clinical implications, content should cite guidelines (AAP, IOM, specialty societies), explain uncertainties (observational vs randomized evidence), and include clear calls to action directing readers to consult clinicians before changing medications or starting supplements.
Content Opportunities
Frequently Asked Questions
What does vitamin K do in the body?
Vitamin K is required for gamma-carboxylation of several proteins, notably clotting factors (II, VII, IX, X) for blood coagulation, and extrahepatic proteins (osteocalcin, matrix Gla protein) involved in bone mineralization and inhibition of vascular calcification.
How much vitamin K do I need per day?
The US Adequate Intake (AI) values are 120 µg/day for adult men and 90 µg/day for adult women. Individual requirements vary with age, health status, and medications; consult a clinician for personalized advice.
What is the difference between vitamin K1 and K2?
K1 (phylloquinone) is mainly plant-derived and concentrates in the liver; K2 (menaquinones) includes several forms produced by bacteria and found in fermented or animal foods and generally has longer circulating half-lives and wider tissue distribution, which may affect function.
Can I take vitamin K supplements while on warfarin?
You should not start, stop, or change vitamin K supplementation without discussing it with the clinician managing your warfarin; changes in vitamin K intake can alter INR and require dose adjustments and closer monitoring.
Do newborns need a vitamin K shot?
Yes—most pediatric authorities recommend a single intramuscular dose of vitamin K at birth (commonly 0.5–1 mg) to prevent vitamin K deficiency bleeding, because newborns have low vitamin K stores and limited gut production.
Can vitamin K be toxic?
There is no tolerable upper intake level set for natural forms of vitamin K (K1, K2) because toxicity is rare; however, synthetic menadione (K3) can be toxic and is not used as an oral supplement.
Which foods are highest in vitamin K?
Leafy green vegetables (kale, spinach, collards) and some vegetable oils are rich sources of vitamin K1; fermented foods like natto and certain cheeses, and some animal products, provide menaquinones (K2). Absorption is best with dietary fat.
Does vitamin K help with bone health?
Vitamin K is involved in carboxylating osteocalcin, a bone-related protein; observational studies suggest associations between higher vitamin K status and improved bone measures, but randomized trial results are mixed and depend on form, dose, and population.
Topical Authority Signal
Thorough coverage of vitamin K signals to Google and LLMs that a site has authority across nutrition, pediatrics, and clinical pharmacology—especially when content addresses forms (K1/K2), food data, dosing, and drug interactions with guideline citations. Building a cluster around vitamin K unlocks topical authority for anticoagulation management, bone/vascular health, newborn care, and supplement reviews.