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📰Read the full Vitamin K evidence review on GMJ News →Complete clinical article, references and updates on news.gmj.ge. This page is the structured safety summary.⚠ Any neonate who did not receive vitamin K prophylaxis — risk of late VKDB with intracranial hemorrhage [6]
⚠ Unexplained bleeding in a patient on prolonged antibiotics — check PT/INR and administer vitamin K [3]
⚠ Patients on warfarin — counsel on maintaining consistent (not zero) vitamin K intake [3]
⚠ Postmenopausal women with osteopenia — consider MK-7 (180 µg/day) as adjunct to calcium and vitamin D [8]
🥗 Food first — build your daily 120 mcg/ 90 mcg
Check the foods you regularly eat — the bar fills toward your daily target.
Natto (100 g)1,103 mcg
Kale, cooked (125 mL)531 mcg
Spinach, cooked (125 mL)444 mcg
Collard greens, cooked (125 mL)418 mcg
Broccoli, cooked (125 mL)110 mcg
Brussels sprouts (125 mL)109 mcg
Soybean oil (1 tbsp)25 mcg
Hard cheese (28 g)10 mcg
Check your regular foods above
☑ Risk checker
Neonates — limited placental transfer and low breast milk content [6]
Prolonged broad-spectrum antibiotic therapy [3]
Fat malabsorption (celiac disease, Crohn disease, short bowel, cholestasis) [3]
Chronic liver disease (impaired storage and utilization) [3]
Warfarin therapy (functional vitamin K antagonism) [3]
Extremely restricted diets without green vegetables [1]
Select factors
🔬 Lab interpreter
Recommended test
Prothrombin time (PT) / INR
Prothrombin time (PT) / INR
Reference range / target
PT 11–13.5 seconds; INR 1.0 (unless anticoagulated)
PT 11–13.5 seconds; INR 1.0 (unless anticoagulated)
The standard clinical test for vitamin K-dependent coagulation. Prolonged PT indicates significant depletion of hepatic clotting factors [3].
Full lab monitoring ↓⚕ For professionals — confirm ranges against your local laboratory.
Clinical verdict
Vitamin K1 is well supplied by green leafy vegetables and is critical for coagulation. Vitamin K2 (MK-7) has a distinct role in extrahepatic carboxylation — activating osteocalcin for bone mineralization and matrix Gla protein for vascular protection. Neonatal vitamin K prophylaxis prevents a rare but potentially fatal hemorrhagic disease [3] [6].
1 How much do I need?
👤 Adults: Specific dosage data under clinical review
👴 Elderly: Specific dosage data under clinical review
🤰 Pregnancy: Specific dosage data under clinical review
👦 Pediatric: Specific dosage data under clinical review
🏃 Athletes: Standard dose
⚖️ Obesity: Standard dose
Fat-soluble compounds may require dose adjustment in obesity.
🩺 Renal: Consult specialist
Dose adjustment may be needed in renal impairment.
🌱 Vegan: Standard dose
How to take
🍽 Timing: Take with a meal containing fat. K1 absorption increases up to 10-fold when consumed with dietary fat versus fasting [1].
💊 With food: Olive oil, nuts, cheese, or avocado alongside green vegetables dramatically improve K1 absorption. Raw salads without oil dressing provide much less bioavailable K1 [1].
2 Which form?
| Form | Bioavailability | Vegan | Cost |
|---|---|---|---|
| ['Phylloquinone (K1)', 'common', 'Primary dietary form from green vegetables. Absorbed in the proximal intestine with dietary fat. Rapidly cleared from plasma. Primarily supports hepatic coagulation factor synthesis [1].'] | Standard | Check label | |
| ['Menaquinone-4 (MK-4)', '', 'Tissue-converted form. Present in animal products (meat, eggs, dairy). Short half-life similar to K1. Used in Japan at pharmacological doses (45 mg/day) for osteoporosis [4].'] | Standard | Check label | |
| ['Menaquinone-7 (MK-7)', 'preferred', 'Produced by Bacillus subtilis fermentation (natto). Longest half-life (~72 hours) of all vitamin K forms, producing sustained activation of extrahepatic proteins (osteocalcin, MGP). Increasingly recommended for bone and vascular health [4].'] | Standard | Check label |
3 Common questions
Should I avoid vitamin K if I take warfarin? ▼
No — the goal is consistency, not avoidance. Maintain a stable daily vitamin K intake so that INR remains predictable. Sudden increases or decreases in K1-rich food intake will destabilize anticoagulation [3]. Inform your anticoagulation clinic about your dietary habits.
Is K2 (MK-7) better than K1 for bone health? ▼
MK-7 has a longer half-life (~72 hours vs ~2 hours for K1) and more effectively activates osteocalcin in extrahepatic tissues [4]. Clinical trials suggest MK-7 at 180 µg/day may slow bone loss in postmenopausal women [8]. However, K1 adequately supports coagulation. Both forms have complementary roles.
Why do newborns receive a vitamin K injection? ▼
Neonates have very low vitamin K stores due to poor placental transfer and low breast milk content. Without prophylaxis, 0.25–1.7% develop vitamin K deficiency bleeding (VKDB), which can include fatal intracranial hemorrhage [6]. A single 1 mg intramuscular injection at birth effectively prevents this.
Can I get enough vitamin K from diet alone? ▼
Most people eating green vegetables regularly meet the AI (90–120 µg/day). However, K2 (especially MK-7) intake is typically low unless fermented foods (natto, certain cheeses) are consumed [4]. Supplementation with MK-7 may be beneficial for bone and vascular health beyond what diet alone provides [8].
4 Clinical evidence
Strong
Essential role in blood coagulation: vitamin K deficiency leads to prolonged prothrombin time and hemorrhagic diathesis [3]. Neonatal hemorrhagic disease prevention: a single intramuscular dose of 1 mg vitamin K at birth prevents vitamin K deficiency bleeding (VKDB), which occurs in 0.25–1.7% of newborns without prophylaxis [6]. Warfarin reversal: intravenous vitamin K corrects supratherapeutic INR within 12–24 hours [3]. HIGH
Moderate
Bone health: MK-4 at pharmacological doses (45 mg/day) reduced vertebral fracture risk in Japanese postmenopausal women [7]. MK-7 supplementation (180 µg/day for 3 years) reduced age-related bone loss and improved bone strength in the Knapen et al. trial (n = 244) [8]. Vascular calcification: MK-7 at 360 µg/day for 2 years improved arterial stiffness in postmenopausal women in the VitaK-CAC trial [9]. MODERATE
Insufficient
Cancer prevention: observational studies suggest inverse associations between vitamin K intake and cancer risk, but randomized trial data are lacking [2]. Cognitive function: preliminary data link vitamin K status to cognitive performance in older adults, but interventional evidence is insufficient [2]. Diabetes prevention: epidemiological associations require confirmation [2]. LOW
5 Safety, toxicity & adverse events
Absolute contraindications
✕ Concurrent warfarin therapy without INR monitoring (K1 antagonizes warfarin)
Relative
⚠ Severe liver disease
⚠ Oral anticoagulants — maintain consistent K intake rather than avoiding
🚩 Red flags
● Neonate with unexplained bleeding who did not receive vitamin K at birth — administer IM K1 immediately and evaluate for VKDB [6]
● Patient on warfarin with sudden increase in green vegetable intake — recheck INR within 3–5 days [3]
● Prolonged PT/INR in a malnourished patient on long-term antibiotics — administer vitamin K and investigate [3]
● Unexplained bruising in an infant aged 2–12 weeks — consider late VKDB even if prophylaxis was given orally [6]
6 Interactions
Drug interactions
Warfarin (coumarins) Major
Mechanism: Warfarin inhibits vitamin K epoxide reductase (VKORC1). Dietary or supplemental vitamin K provides substrate that bypasses warfarin's block, reducing anticoagulant effect. [3]
Effect: Variable INR. Subtherapeutic anticoagulation if K intake increases; supratherapeutic if K intake drops. [3]
Action: Maintain consistent daily vitamin K intake. Do not take K supplements without anticoagulation team guidance. Monitor INR when diet changes [3].
Broad-spectrum antibiotics (fluoroquinolones, cephalosporins) Moderate
Mechanism: Prolonged antibiotic courses disrupt intestinal flora that produce menaquinones. In malnourished patients, this may precipitate deficiency. [3]
Effect: Prolonged PT/INR. Clinically significant bleeding in vulnerable patients. [3]
Action: Monitor PT/INR during prolonged antibiotic courses, especially in ICU and malnourished patients [3].
Orlistat Moderate
Mechanism: Reduces dietary fat absorption by ~30%, proportionally decreasing fat-soluble vitamin absorption. [5]
Effect: Reduced vitamin K absorption with chronic use. [5]
Action: Take vitamin K supplement at least 2 hours before or after orlistat [5].
Cholestyramine Moderate
Mechanism: Bile acid sequestrant binds fat-soluble vitamins in the intestinal lumen. [5]
Effect: Reduced vitamin K absorption. [5]
Action: Separate vitamin K from cholestyramine by 4+ hours [5].
Supplement synergies
Vitamin D · 1,000–2,000 IU/day vitamin D + 100–200 µg/day MK-7
Vitamin D enhances intestinal calcium absorption; vitamin K2 activates osteocalcin to direct calcium into bone and matrix Gla protein to prevent arterial calcification [4].
Vitamin D enhances intestinal calcium absorption; vitamin K2 activates osteocalcin to direct calcium into bone and matrix Gla protein to prevent arterial calcification [4].
Calcium · 500–1,200 mg/day calcium
Vitamin K ensures calcium is deposited in bone rather than soft tissue. Calcium + D + K2 is the complete triad for bone health [8].
Vitamin K ensures calcium is deposited in bone rather than soft tissue. Calcium + D + K2 is the complete triad for bone health [8].
Magnesium · 320–420 mg/day
Magnesium is required for vitamin D metabolism and indirectly supports vitamin K-dependent bone mineralization pathways [1].
Magnesium is required for vitamin D metabolism and indirectly supports vitamin K-dependent bone mineralization pathways [1].
7 Regulatory
United States (FDA): Classified as a dietary supplement (K1 and K2). No RDA established — only Adequate Intake. Injectable K1 is prescription-only for coagulopathy. No UL established due to lack of toxicity data [1].
European Union (EFSA): Authorized health claims for blood coagulation and bone health maintenance [10]. Both K1 and MK-7 are permitted in supplements. No UL established.
Japan (MHLW): MK-4 at 45 mg/day approved as pharmaceutical for osteoporosis treatment (Glakay). K2 supplements widely available. AI: 150 µg/day for adults.
South Korea (MFDS): Registered health functional food ingredient (K1 and K2). Approved claims: blood coagulation and bone health.
8 US supplement products
567
on-market products containing Vitamin K (NIH DSLD)
Brands carrying Vitamin K (216)
Click a brand to see its Vitamin K products.
9 Frequently paired with
10 Cite this page
Vancouver: Pkhakadze G. Vitamin K — safety profile [Internet]. Tbilisi: PHIG; 2026 [cited 2026 Aug 15]. Available from: https://supplement.ge/ingredients/vitamin-k/
APA 7th: Pkhakadze, G. (2026). Vitamin K — Safety profile. Public Health Institute of Georgia. https://supplement.ge/ingredients/vitamin-k/
📋 Editorial information
Author: Prof. G. Pkhakadze, MD, MPH, PhD
Institution: Public Health Institute of Georgia (PHIG)
Affiliation: David Tvildiani Medical University (DTMU)
First published: January 2026
Last reviewed: 2026-05-29
Next review: February 2027
References: 10 cited sources
COI: SupplementIndex receives no funding from supplement manufacturers. All content independently authored by PHIG.
Process: Systematic literature review
📄 License & reuse
Published under Creative Commons Attribution 4.0 International (CC BY 4.0). You may share and adapt for any purpose with attribution.
Pkhakadze G. "Vitamin K — Safety Profile." SupplementIndex, PHIG, 2026. https://supplement.ge/ingredients/vitamin-k/ CC BY 4.0.
GP
Prof. G. Pkhakadze, MD, MPH, PhD
Professor of Public Health · Head of Department, DTMU
Editor-in-Chief, Georgian Medical Journal (ISSN 3088-4322)
Chair, Public Health Institute of Georgia · UEMS Public Health Section
Educational and public health purposes. CC BY 4.0. Consult your healthcare provider before starting any supplement. Corrections: info@accreditation.ge. Publisher: PHIG