Guides
Vitamin K and Warfarin: Consistent Intake, K2 and Bone Health
If you take warfarin, do not avoid green vegetables; eat a similar amount every day. It is not certain that K2 strengthens bone; TEMD 2025 does not recommend it routinely.
Translated from the Turkish original by DoktorClub. The Turkish version is the reference text; this English translation has not been separately reviewed by a physician. Read the Turkish original.
Key takeaway
If you take warfarin, you do not need to avoid green vegetables. According to NIH ODS, what matters is getting a similar amount of vitamin K every day. Sudden increases or decreases change the drug's effect. Apixaban, dabigatran, edoxaban and rivaroxaban, on the other hand, do not work through vitamin K. It is not certain that vitamin K2 strengthens bone; the TEMD 2025 guideline does not accept vitamin K as a standard recommendation in osteoporosis.
Short Answer
If you take warfarin, you do not need to avoid green vegetables. According to NIH ODS, what matters is getting a similar amount of vitamin K every day. Sudden increases or decreases change the drug's effect. Apixaban, dabigatran, edoxaban and rivaroxaban, on the other hand, do not work through vitamin K. It is not certain that vitamin K2 strengthens bone; the TEMD 2025 guideline does not accept vitamin K as a standard recommendation in osteoporosis.
What does it do?
Vitamin K contributes to normal blood clotting. It activates certain clotting proteins in the liver. It also contributes to the maintenance of normal bones. According to TEMD 2025, it plays a role in calcium binding by a bone protein called osteocalcin.
It has two main forms:
- K1 (phylloquinone): Found in green leafy vegetables. This is the main vitamin K in the diet.
- K2 (menaquinones): Found in fermented foods and some animal products. Gut bacteria also produce it. The MK-4 and MK-7 forms are most commonly used in supplements.
How does warfarin work? According to NIH ODS, warfarin works against vitamin K and reduces vitamin K-dependent clotting factors. That is why sudden changes in vitamin K intake shift the drug's effect.
Daily requirement
The requirement varies by age and sex. The values are for healthy people.
| Group | EFSA 2017 / TÜBER 2022 (adequate intake) | NIH ODS / IOM (adequate intake) |
|---|---|---|
| Adult man | 70 µg/day | 120 µg/day |
| Adult woman | 70 µg/day | 90 µg/day |
| Pregnancy and breastfeeding | 70 µg/day | 90 µg/day |
| Ages 1–3 | 12 µg/day | 30 µg/day |
| Infant 0–6 months | — | 2.0 µg/day |
The EFSA values are for K1 only. According to EFSA 2017, there are not enough data to set a requirement value for K2.
Which foods contain it?
According to TÜBER 2022 (the Turkish Ministry of Health's Türkiye Nutrition Guide), sources of vitamin K are dark green leafy vegetables, liver, eggs and cheese. According to NIH ODS, vegetable oils and some fruits also contain K1. In Turkish cuisine, spinach, chard, purslane, parsley, arugula, cabbage and broccoli belong to this group.
Some examples from the NIH ODS food table are:
- Spinach (1 cup, raw): 145 µg.
- Collard greens (1 cup, raw): 113 µg.
- Broccoli (half a cup, boiled): 110 µg.
- Natto (Japanese fermented soybeans, about 85 g): 850 µg; in the MK-7 form.
Fermented foods such as cheese also contain some K2. But in Turkish cuisine the main source is green leafy vegetables.
Who is at risk of deficiency?
Deficiency is rare in healthy adults. According to NIH ODS, the risk groups are:
- Newborns who did not receive vitamin K at birth: Little vitamin K passes from the placenta to the baby. Deficiency can lead to bleeding (vitamin K deficiency bleeding of the newborn).
- People with malabsorption: Cystic fibrosis, celiac disease, ulcerative colitis, short bowel syndrome.
- People who have had bariatric (obesity) surgery.
- People on long-term antibiotics: Especially when use exceeding several weeks is combined with low vitamin K intake.
Possible symptoms: Easy bruising, gum or nose bleeding, prolonged bleeding. According to NIH ODS, newborns may bleed from the umbilicus, the gastrointestinal tract, the skin or the nose. These symptoms also occur in other bleeding disorders.
Which test, and how is it read?
Vitamin K levels are not measured routinely. Clotting tests provide indirect information.
- PT/INR: Prolonged in vitamin K deficiency. It is the test monitored regularly in people taking warfarin. For details, see the INR and PT guide.
- In people taking warfarin: An unexpected fall or rise in INR may be due to a sudden change in diet. A new supplement or antibiotic can also be the cause.
Vitamin K is not tested for bone health. Bone density measurement (DEXA) and risk assessment are the basis. Our osteoporosis guide explains this.
When is a supplement needed, and when not?
The situation where it is definitely needed: the newborn. According to NIH ODS, the American Academy of Pediatrics recommends a single intramuscular dose of 0.5–1 mg K1 at birth. In Türkiye, too, all newborns receive a single dose after birth.
Does vitamin K2 strengthen bone? The short answer to this question is "not certain":
- A meta-analysis published in 2022 examined 16 randomized trials including 6,425 postmenopausal women. In the K2 group, lumbar spine bone density increased. This effect was seen mostly in combination with another treatment; with K2 alone the difference was not significant. There was no significant difference at the hip or femoral neck.
- In the same analysis, fracture frequency did not decrease significantly in the overall calculation. A decrease was seen when one study was excluded. But the excluded study was the largest, including more than two-thirds of the women.
- Most of the studies were from Japan, and most used 45 mg of K2 a day. Some studies had a high risk of bias.
- According to NIH ODS, 45 mg of MK-4 is used as a drug for osteoporosis in Japan. This dose is far higher than the microgram-level supplements on the market.
- According to TEMD 2025, vitamin K is not a standard recommendation because the findings have not been confirmed in other populations.
The steps with strong evidence for bone are adequate calcium and vitamin D, exercise and fall prevention. If osteoporosis is diagnosed, the drug treatment recommended by the doctor is the mainstay.
Vascular calcification: According to NIH ODS, K2 intake was associated with less coronary calcification in observational studies. Such studies do not show cause and effect; the topic is still being researched.
Upper limit and excess
EFSA and IOM have not set an upper limit for vitamin K. According to IOM, the reason is its low potential for toxicity. EFSA states that there are insufficient data.
This does not mean it is safe without limit for everyone. For someone taking warfarin, the real risk is a sudden high intake. Starting a K2 supplement can lower INR and increase clot risk.
The hidden overlap trap: Vitamin K is found in multivitamins, "bone support" products and D3+K2 combinations. Check the K1 and K2 amounts on the labels.
Drug and test interactions
- Warfarin: According to NIH ODS, sudden changes in vitamin K intake can increase or decrease the drug's effect. Tell your doctor before changing your diet substantially.
- Newer anticoagulants (apixaban, dabigatran, edoxaban, rivaroxaban): These are not vitamin K antagonists. According to the EHRA 2021 guide, apixaban, dabigatran and edoxaban have no significant food interactions. The 15 and 20 mg doses of rivaroxaban, however, should be taken with food.
- Orlistat (weight-loss drug): According to NIH ODS, it can reduce vitamin K absorption. When used with warfarin, it can markedly prolong PT.
- Antibiotics (especially cephalosporins): According to NIH ODS, they can affect vitamin K status.
- Bile acid sequestrants: According to NIH ODS, they can reduce vitamin K absorption.
- High-dose vitamin E: According to NIH ODS, it can counteract vitamin K-dependent clotting factors.
If you use one of these drugs, tell your doctor or pharmacist. Do not stop or change your medication on your own.
In Türkiye
- Newborn practice: According to the November 2021 circular of the Turkish Ministry of Health reported by Anadolu Agency, all newborns receive a single dose of vitamin K after birth. The dose is set by birth weight; for babies under 1,500 g it is 0.5 mg intramuscularly.
- Osteoporosis guideline: TEMD 2025 does not accept vitamin K as a standard recommendation for the prevention and treatment of osteoporosis.
- Warfarin and bone: According to TEMD 2025, the clinical significance of warfarin's effect on bone is unclear. No warfarin-specific bone measure is needed. If osteoporosis risk is high, the guideline recommends adequate calcium and vitamin D intake.
- Supplement approval: According to the Ministry of Agriculture and Forestry, food supplements are not drugs and are not used to treat disease. You can check approved products at ggbs.tarim.gov.tr.
Which doctor should you see?
- If you take warfarin: The Cardiology or Internal Medicine doctor who prescribed the drug; the unit that monitors your INR.
- Osteoporosis and the K2 question: Endocrinology or Physical Medicine and Rehabilitation.
- Easy bruising, unexplained bleeding: Internal Medicine; Hematology if needed.
- Newborns and infants: Pediatrics.
- Bring with you: Supplement boxes (especially D3+K2 products), your medication list and your latest INR results.
When should you seek emergency care?
- If you have black stools, bloody vomit, blood in the urine or bleeding that will not stop while taking warfarin, go to the emergency department without delay. If there is fainting, vomiting of blood or heavy bleeding, call 112 (the emergency number in Türkiye).
- If there is a sudden severe headache, facial droop, arm weakness or speech disturbance, call 112.
- Sudden shortness of breath, chest pain or coughing up blood may indicate a clot in the lung; call 112.
- New swelling, pain or redness in one leg may indicate a clot in a vein; see a doctor the same day.
- If a baby in the first 3 months has bleeding from the umbilicus or nose, blood in vomit or stool, bruising or pallor, go to the emergency department immediately; if there is a seizure, call 112.
- If the laboratory has notified you that your INR is very high, contact your doctor the same day.
- If a child has swallowed an anticoagulant drug, call the National Poison Information Center (114) without waiting for symptoms; if there is bleeding or a change in consciousness, call 112.
Related guides
- Vitamin and Mineral Guide
- INR and PT values
- Osteoporosis guide
- Calcium supplements: bone or blood vessels?
- Vitamin E supplements
- Supplement and drug interactions
- Drug interaction tool
What changed? (October 2026)
- The article "Does vitamin K2 strengthen bone?" was merged into this guide. The K2 section was rewritten according to TEMD 2025 and the 2022 meta-analysis.
- The principle of consistent vitamin K intake for people taking warfarin (NIH ODS) was explained.
- Symptoms of a clot in the leg and a clot in the lung were separated; nutrition guide information was updated according to TÜBER 2022.
- The newborn vitamin K circular in Türkiye and EHRA 2021 information on newer anticoagulants were added.
Sources
- Türkiye Endokrinoloji ve Metabolizma Derneği. Osteoporoz ve Metabolik Kemik Hastalıkları Tanı ve Tedavi Kılavuzu. 17th edition, April 2025. https://file.temd.org.tr/Uploads/publications/guides/documents/OSTEPOROZ_nisan2025.pdf (accessed October 3, 2026)
- Sağlık Bakanlığı. Türkiye Beslenme Rehberi (TÜBER) 2022. https://hsgm.saglik.gov.tr/depo/birimler/saglikli-beslenme-ve-hareketli-hayat-db/Dokumanlar/Rehberler/Turkiye_Beslenme_Rehber_TUBER_2022_min.pdf (accessed October 4, 2026)
- Anadolu Ajansı. Sağlık Bakanlığından yenidoğanlar için "K vitamini" genelgesi. November 5, 2021. https://www.aa.com.tr/tr/saglik/saglik-bakanligindan-yenidoganlar-icin-k-vitamini-genelgesi/2412810 (accessed October 4, 2026)
- T.C. Tarım ve Orman Bakanlığı. Güvenilir Gıda: Takviye Edici Gıda. https://guvenilirgida.tarimorman.gov.tr/Sayfa/Detay/1882 (accessed October 4, 2026)
- EFSA NDA Panel. Dietary reference values for vitamin K. EFSA Journal 2017;15(5):4780. https://doi.org/10.2903/j.efsa.2017.4780 (accessed October 4, 2026)
- NIH Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals. Updated March 29, 2021. https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/ (accessed October 4, 2026)
- Steffel J et al. 2021 European Heart Rhythm Association Practical Guide on the Use of Non-Vitamin K Antagonist Oral Anticoagulants in Patients with Atrial Fibrillation. Europace 2021;23(10):1612-1676. https://academic.oup.com/europace/article/23/10/1612/6247378 (accessed October 4, 2026)
- Ma ML et al. Efficacy of vitamin K2 in the prevention and treatment of postmenopausal osteoporosis: a systematic review and meta-analysis of randomized controlled trials. Front Public Health 2022;10:979649. https://doi.org/10.3389/fpubh.2022.979649 (accessed October 4, 2026)
- EFSA. Overview on Tolerable Upper Intake Levels. Version 11, August 2025. https://www.efsa.europa.eu/sites/default/files/2024-05/ul-summary-report.pdf (accessed October 4, 2026)
- NIH Office of Dietary Supplements. Vitamin E: Fact Sheet for Health Professionals. Updated March 26, 2021. https://ods.od.nih.gov/factsheets/VitaminE-HealthProfessional/ (accessed October 4, 2026)
Frequently asked questions
Can people taking warfarin eat green vegetables?
Yes, they can. According to NIH ODS, what matters is getting a similar amount of vitamin K every day. The problem is eating no greens one week and a lot the next. If you are going to change your diet substantially, tell the doctor who monitors your INR.
Does vitamin K2 strengthen bone?
It is not certain. In one meta-analysis, bone density at the lumbar spine increased, but the effect on fractures was not consistent. Most studies were from Japan and used drug-level doses. TEMD 2025 does not accept vitamin K as a standard recommendation in osteoporosis.
Can I take a K2 supplement while on warfarin?
Do not take it without consulting your doctor. K2 can lower INR by reducing warfarin's effect. This can increase clot risk. If your doctor considers it necessary, they will monitor your INR more often.
Is vitamin K a problem while taking apixaban or rivaroxaban?
These drugs do not work through the vitamin K pathway; a steady vitamin K intake as with warfarin is not required. The package leaflet and your pharmacist will tell you whether to take the drug with food or on an empty stomach. Still, tell your doctor or pharmacist about any new supplement.
Why are newborns given a vitamin K injection?
Babies are born with low vitamin K stores. According to NIH ODS, late bleeding can occur between weeks 2 and 12, especially in exclusively breastfed babies. This bleeding can occur inside the brain and can be fatal. In Türkiye, all newborns receive a single dose of vitamin K after birth.
