Vitamin K: K1 vs K2 (MK-4, MK-7), Food Sources and Anticoagulants
Vitamin K explained: K1 versus K2 (MK-4, MK-7), food sources, official intake levels, rare deficiency, newborn use, bone and heart research, and the warfarin interaction.
Content last updated . This page has not been medically reviewed.
What is Vitamin K good for?
What the body uses it for, and how strong the evidence is. A normal job in the body is not proof that extra supplements add benefit; each card says which.
Blood clotting
Established roleVitamin K helps the liver make the proteins that let blood clot. Without it, blood would not clot properly.
Supplements: Supplements correct a deficiency; no good evidence of extra benefit from supplements when intake is adequate.
Preventing bleeding in newborns
Clinically supportedNewborns have low vitamin K and can bleed in the first weeks of life, so a dose is given soon after birth in many countries.
Supplements: This is a medical dose given to babies, not a supplement choice for parents. Ask your midwife or paediatrician.
Wound healing
Established roleVitamin K is needed for blood clotting and wound healing.
Supplements: Supplements correct a deficiency; no good evidence of extra benefit from supplements when intake is adequate.
Bone health
Not enough evidenceThe NHS says there is some evidence vitamin K may help keep bones healthy, but trials have not confirmed a benefit.
Supplements: Evidence is insufficient to recommend supplements for bone density or fracture prevention.
Calcium build-up in heart arteries
Preliminary or mixedA 2-year trial of MK-7 in people with coronary disease found slower progression of coronary artery calcium; the clinical meaning is not yet known.
Supplements: Preliminary: a single trial, no proof of fewer heart events.
Steadier warfarin control
Preliminary or mixedIn one trial, a small daily oral vitamin K dose, given under clinical supervision, improved time in the target range for people with unstable warfarin control.
Supplements: Clinician-supervised use only; not a do-it-yourself plan.
Supply from food and gut bacteria
Established roleLeafy green vegetables are the main source of K1; bacteria in the lower gut also make some vitamin K.
Supplements: Food covers needs for most people; the body stores surplus in the liver (NHS).
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Body systems (1)
- Hepatic / Liver SystemEstablished role
The liver needs vitamin K to make clotting factors. This is about normal biology, not a reason to supplement.
Body parts (2)
- LiverEstablished role
The liver uses vitamin K to make clotting factors II, VII, IX and X.
- Large IntestineEstablished role
Bacteria in the lower gut make some vitamin K; poor gut absorption is a cause of deficiency.
Root causes (3)
- Medication Side EffectsDocumented risk
Long-term antibiotic treatment can lead to deficiency, and vitamin K weakens the effect of warfarin.
- Digestive DysfunctionDeficiency link
Deficiency can happen when the gut cannot absorb the vitamin.
- Nutrient DeficiencyDeficiency link
Vitamin K deficiency is rare in adults but is linked to easier bruising and bleeding.
Habits (1)
- Balanced NutritionEstablished role
Green leafy vegetables are the main food source; a varied diet should provide enough, and people on warfarin are asked to keep intake steady.
Conditions & symptoms (3)
- Vitamin K DeficiencyDeficiency link
Lack of vitamin K leads to easier bruising and bleeding. It is rare in adults.
- Increased Tendency To BruiseDeficiency link
Easier bruising is a sign of vitamin K deficiency, but has many other causes; see a clinician.
- Malabsorption SyndromeDeficiency link
Poor absorption in the gut is a cause of vitamin K deficiency.
Documented risks and interactions (1)
- Interaction with warfarin. Vitamin K works against the blood thinner warfarin, so sudden changes in intake can change how the drug works.
Urgent for people on warfarin
If you take the blood thinner warfarin, vitamin K changes how it works. The NHS (UK) says not to take vitamin K supplements while on warfarin, and that foods high in vitamin K, such as broccoli, spinach and other leafy greens, can affect it: you can still eat them, but talk to your warfarin clinic. [1] MedlinePlus says what matters most is keeping vitamin K intake steady from day to day, because sudden changes alter the drug's effect. [2] Do not stop or change a prescribed medicine on your own. Details: Vitamins and blood thinners.Overview
Vitamin K is known as the clotting vitamin: the liver needs it to make clotting factors II, VII, IX and X, and without it blood would not clot. [2] The NHS adds that there is some evidence it may help keep bones healthy. [3] For most adults deficiency is very rare. [2]Evidence labels used: established nutritional role / deficiency treatment, promising but limited, mixed, insufficient evidence. Proper evidence not found means we looked and found nothing usable.
K1, K2, MK-4 and MK-7
MedlinePlus lists phylloquinone (K1) and menaquinone (K2), and names menadione (K3) as well; bacteria in the lower gut also make vitamin K. [2] Leafy vegetables are the main K1 source. [2] One small study of healthy Japanese women found MK-7 well absorbed, while MK-4 from a single dose was not detectable in blood and did not raise blood MK-4 over 7 days of use; the authors concluded that MK-4 in food does not contribute to vitamin K status as measured by blood levels. [4] That is one study of blood levels, not of health outcomes. The heart trial below used MK-7. Do not carry results from one form to another. See Vitamin K1 vs K2 and Vitamin D3 with K2.Food sources
Green leafy vegetables such as kale, spinach, turnip greens, collards, Swiss chard, mustard greens, parsley, romaine and green leaf lettuce; Brussels sprouts, broccoli, cauliflower and cabbage; smaller amounts in fish, liver, meat, eggs and cereals. [2] The NHS also lists vegetable oils and cereal grains. [3] See Foods high in vitamin K.Who may need assessment
MedlinePlus says deficiency happens when the gut cannot absorb the vitamin and can follow long-term antibiotic treatment. [2] Newborns are a special case (below). A person with unexplained bruising or bleeding needs a clinician, not a supplement. [2]Deficiency
People with deficiency are more likely to bruise and bleed. [2] In newborns, a Cochrane review describes vitamin K deficiency bleeding in the first weeks of life and found one 1 mg intramuscular dose after birth effective for preventing classic bleeding (days 1 to 7), including after circumcision. [5] A 2016 European pediatric position paper says all newborn infants should receive vitamin K prophylaxis. [6] Ask your midwife or pediatrician about practice in your country; see Vitamin D and K for newborns.Official intake levels
There is not enough research to set an RDA, so the US uses an Adequate Intake (AI). [2] These are references for stated groups, not personal advice. See RDA, AI, DV and UL.| Source and year | Population | Amount per day |
|---|---|---|
| NHS (UK), reviewed 2020 | Adults | About 1 mcg per kg of body weight (65 mcg for 65 kg) [3] |
| US DRIs via MedlinePlus (reviewed 2025) | Infants 0 to 6 and 7 to 12 months (AI) | 2.0 and 2.5 mcg [2] |
| Same | Children 1 to 3, 4 to 8, 9 to 13 years (AI) | 30, 55, 60 mcg [2] |
| Same | Ages 14 to 18 including pregnancy and lactation; males 19+; females 19+ including pregnancy and lactation | 75 mcg; 120 mcg; 90 mcg [2] |
| Daily Value on US labels (FDA) | Label reference | 120 mcg [7] |
| NHS (UK) | Supplements: adults | 1 mg (1,000 mcg) or less unlikely to cause harm [3] |
| EFSA (EU), overview August 2025 | Upper level, all groups | No adequate data to derive one [8] |
The NHS says there is not enough evidence to know what happens with high supplement doses. [3] No defined upper limit does not prove high doses are safe. The NIH Office of Dietary Supplements page could not be read this session, so it is not cited.
Evidence by specific use
| Question | What the source found | Label |
|---|---|---|
| Clotting; newborn bleeding | Established role; deficiency causes bleeding [2][5] | Established |
| Steadier warfarin control | 6-month trial, 70 warfarin patients with unstable control, 150 mcg a day of oral vitamin K or placebo: time in target range rose 28% versus 15% [9]. Done under clinical supervision | Promising but limited; not a do-it-yourself plan |
| Bone density and fractures | Review of 36 trials in adults: no evidence of effect on bone density or vertebral fractures in post-menopausal or osteoporotic patients; may reduce clinical fractures but evidence insufficient to confirm [10] | Insufficient evidence |
| Coronary artery calcium | Randomized trial, 180 patients with symptomatic coronary disease, MK-7 for 2 years: slower calcium score progression; clinical significance not yet known [11] | Promising but limited |
Testing and labels
We found no routine vitamin K blood test described for healthy people in the sources read. Check whether a product lists K1, MK-4 or MK-7, the amount in mcg, and any added calcium or vitamin D. See Reading supplement labels, Quality testing and certifications and Vitamin D.Frequently asked questions
Is vitamin K2 better than K1?
Proper evidence not found for a head-to-head comparison on health outcomes. One small study compared blood levels of MK-4 and MK-7 only. [4]
Can I eat salad if I take warfarin?
The NHS says you can still eat foods high in vitamin K but to ask your warfarin clinic, and MedlinePlus stresses keeping intake steady. [1][2]
Do I need a vitamin K supplement for bones?
A 2019 review found insufficient evidence that it prevents fractures or raises bone density. [10]
Why do babies get vitamin K?
Newborns can bleed from low vitamin K; a Cochrane review found one dose after birth reduced bleeding in the first week. [5]
Is vitamin K toxic?
EFSA could not derive an upper limit, and the NHS says 1 mg a day or less is unlikely to cause harm. [8][3]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Cautions
- Medicines: warfarin (above). We did not find a readable source on other anticoagulants or other medicines, so none are claimed. Read How interactions work and ask a pharmacist.
- Surgery and clotting disorders: tell your care team about any vitamin K product. See Vitamins before surgery.
- Pregnancy, kidney and liver disease, older adults: beyond the intake table, no vitamin K supplement advice for these groups was found in the sources we read; ask a clinician. See Pregnancy and breastfeeding safety.
References
- NHS (UK). Warfarin. Read 2026-10-22.
- MedlinePlus, U.S. National Library of Medicine. Vitamin K (encyclopedia article, reviewed 1/21/2025). Read 2026-10-22.
- NHS (UK). Vitamins and minerals: Vitamin K. Page last reviewed 3 August 2020. Read 2026-10-22.
- Schurgers et al. 2012. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutr J. PMID 23140417. Read 2026-10-22.
- Puckett and Offringa 2000. Prophylactic vitamin K for vitamin K deficiency bleeding in neonates. Cochrane Database Syst Rev. PMID 11034761. Read 2026-10-22.
- Mihatsch et al. 2016. Prevention of Vitamin K Deficiency Bleeding in Newborn Infants: A Position Paper by the ESPGHAN Committee on Nutrition. J Pediatr Gastroenterol Nutr. PMID 27050049. Read 2026-10-22.
- U.S. Food and Drug Administration. The Daily Value on the Nutrition and Supplement Facts Labels. Read 2026-10-22.
- European Food Safety Authority. Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA NDA Panel. Version 11, August 2025 (Table 3, vitamins). Read 2026-10-22.
- Sconce et al. 2007. Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin. Blood. PMID 17110451. Read 2026-10-22.
- Mott et al. 2019. Effect of vitamin K on bone mineral density and fractures in adults: an updated systematic review and meta-analysis of randomised controlled trials. Osteoporos Int. PMID 31076817. Read 2026-10-22.
- Vossen et al. 2026. Two Years of Menaquinone-7 Supplementation and Coronary Artery Calcification: A Randomized Clinical Trial. JAMA Cardiol. PMID 42268593. Read 2026-10-22.