Vitamin K

Q: What is vitamin K?

Vitamin K is a fat-soluble vitamin the liver needs to make clotting proteins. Without it blood would not clot. It also has roles in wound healing and, per the NHS, possibly in bones.

Q: What is the difference between K1 and K2?

K1 (phylloquinone) is the main form in leafy vegetables. K2 (menaquinones, such as MK-4 and MK-7) is made by gut bacteria and found in some foods. In one small study MK-7 raised blood levels and MK-4 did not.

Q: Is vitamin K2 better than K1?

No head-to-head trial on health outcomes was read. The forms behave differently in the body, and trials of each answer different questions, so results should not be swapped between them.

Q: Which foods have the most vitamin K?

Leafy greens such as kale, spinach, collards, turnip greens and mustard greens; also broccoli, Brussels sprouts and cabbage. By USDA data a cup of cooked spinach has about 889 mcg of K1 and eggs have under 1 mcg.

Q: Can I eat salad if I take warfarin?

The NHS says you can still eat foods high in vitamin K but should talk to your warfarin clinic. MedlinePlus says to keep intake steady from day to day. A 2016 review found no good evidence for cutting greens.

Q: Why do newborn babies get vitamin K?

Babies are born with low vitamin K and can bleed in the first weeks of life. A Cochrane review found one injection after birth reduced bleeding in the first week, and a European position paper says all newborns should get it. Ask your midwife or paediatrician about the plan.

Q: Does vitamin K help bones?

Mixed. A 2019 review of 36 trials found no clear effect on density at most sites or on vertebral fractures and called the evidence insufficient. Some K2 trials found small density gains at the lumbar spine.

Q: Does vitamin K protect the heart or arteries?

Not shown yet. One 2-year MK-7 trial slowed coronary calcium score progression, but the authors say the clinical meaning is unknown. A pooled analysis found no clear effect on blood fats or CRP, and trials in dialysis patients did not clearly change calcification scores.

Q: Does vitamin K help blood sugar?

Small marker changes were seen in a few moderate-quality trials in prediabetes and type 2 diabetes (fasting glucose, HbA1c, HOMA-IR). That is not proof of better diabetes control, and people on diabetes medicines should ask a doctor first.

Q: Is there an upper limit for vitamin K?

EFSA's 2025 overview says there are no adequate data to set one. The NHS says 1 mg or less of supplements a day is unlikely to cause harm and that effects of higher amounts are not known. No upper limit is not proof of safety at any amount.

Phylloquinone (K1) and menaquinones (K2) · also called Vitamina K, K1, K2, the clotting vitamin

Vitamin K is the clotting vitamin: the liver needs it to make the proteins that let blood clot. Leafy greens are the main food source, and real deficiency is rare in adults. It is given to newborns to prevent bleeding. Evidence that pills help bones or arteries is mixed or weak, and vitamin K changes how the blood thinner warfarin works, so ask your doctor or warfarin clinic first.

General information, not medical advice. Last substantive update October 26, 2026 · Not medically reviewed. A named clinician has not signed off on this page. How this page is made

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About Vitamin K

Vitamin K is a fat-soluble vitamin the body needs to make clotting proteins. Greens give most of it, and deficiency is rare. Newborns are given it to prevent bleeding. Pills have mixed or weak evidence for bones and arteries, and vitamin K opposes warfarin.

What vitamin K is

MedlinePlus calls vitamin K the clotting vitamin. The body needs it to make clotting factors II, VII, IX and X in the liver; without it, blood would not clot. It is fat-soluble, so the body stores it in the liver and other tissues, including bone, brain, heart and pancreas. The NHS adds wound healing as a role and says you should be able to get all you need from a varied diet. Gut bacteria also make some vitamin K.

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K1, K2 (MK-4, MK-7) and K3

Vitamin K is a family. Phylloquinone (K1) is the main form in leafy vegetables. Menaquinones (K2) include MK-4 and MK-7. MedlinePlus also names menadione (K3). The forms act differently in the body. In one small study of healthy Japanese women, MK-7 was well absorbed and still detectable in blood after 48 hours, while MK-4 at nutritional doses was not detectable in blood. That study measured blood levels, not health outcomes.

Trials use different forms: MK-4 (as the medicine menatetrenone) in Japanese osteoporosis trials, MK-7 in a bone trial and a coronary calcium trial, and K1 in the warfarin and newborn trials. Do not carry a result from one form to another. We read no head-to-head trial of K1 against K2 on health outcomes.

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Where vitamin K comes from in food

Green leafy vegetables are the main source of K1. USDA data (K1 per cup of cooked vegetable): kale about 494 mcg, spinach about 889 mcg, collards about 773 mcg, turnip greens about 529 mcg and mustard greens about 830 mcg. Half a cup of cooked broccoli has about 110 mcg and half a cup of cooked Brussels sprouts about 109 mcg. A cup of raw cabbage has about 68 mcg and a cup of raw romaine about 48 mcg.

Oils differ: per tablespoon, soybean oil about 25 mcg, canola about 10 mcg and olive about 8 mcg. Eggs, chicken, beef and cheddar have under 1 mcg per portion. USDA's tables give little on K2 foods, so no K2 amounts are given here. The US label reference (Daily Value) is 120 mcg a day (FDA, 2024), so one cup of cooked greens can hold several times that.

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Low vitamin K and who is at risk

MedlinePlus says deficiency is very rare. It happens when the gut cannot absorb vitamin K, or after long-term antibiotic treatment, and people with deficiency are often more likely to bruise and bleed. Easy bruising has many other causes, so unexplained bruising or bleeding needs a clinician, not a supplement. Newborns are a special case: they are born with low vitamin K and can bleed in the first weeks of life.

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What the research shows

The strongest evidence is for newborns: a Cochrane review found one injection after birth reduced bleeding on days 1 to 7, and a European position paper says all newborns should get vitamin K. For bones, results are mixed: some pooled K2 trials found slightly higher lumbar spine density, but the broadest updated review (36 trials) found no clear effect on density at most sites or on vertebral fractures and called the evidence insufficient. A 2-year MK-7 trial in 180 people slowed coronary calcium score progression; the clinical meaning is not yet known. In people on dialysis, vitamin K lowered a blood marker but did not clearly change calcification scores or survival.

Heart-risk and blood-sugar results are small marker changes from moderate-quality trials. Observational studies link more vitamin K1 from food with fewer fractures, but that does not prove cause.

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Warfarin and other cautions

Vitamin K works against warfarin. The NHS (reviewed February 2026) says not to take vitamin K supplements while on warfarin and to talk to your warfarin clinic about foods high in vitamin K. MedlinePlus says the key is to keep intake steady from day to day. A 2016 review found that cutting greens is not supported and stable eating habits matter more. Do not change a prescribed medicine on your own.

No upper limit has been set: EFSA's 2025 overview says there are no adequate data. The NHS says 1 mg (1,000 mcg) or less of supplements a day is unlikely to cause harm and that effects of high amounts are not known. Rare severe allergic reactions have followed vitamin K injected into a vein in hospital. See the Safety tab.

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Official intake figures

MedlinePlus lists US Adequate Intakes because there is not enough evidence for an RDA: infants 2.0 mcg (0 to 6 months) and 2.5 mcg (7 to 12 months); children 30 mcg (1 to 3 years), 55 mcg (4 to 8) and 60 mcg (9 to 13); ages 14 to 18, 75 mcg; males 19 and over, 120 mcg; females 19 and over, 90 mcg (including pregnancy and breastfeeding). The NHS suggests about 1 mcg per kilogram of body weight for adults. These are reference figures, not personal advice.

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Food versus pills

Most trials above are of pills, often K2 forms. Food gives mainly K1 along with other nutrients, and observational studies of food K1 are not trials. No trial compared food vitamin K with pills. This page gives no amounts to take; if you wonder about your own needs, ask a doctor, pharmacist or dietitian.

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At a glance

Traditional uses history, not proof

An essential nutrient from green leafy vegetables
Given to newborns in many countries to prevent bleeding
Sold as K1 or K2 (MK-4, MK-7) supplements for bones and arteries

Studied for research

Blood clotting and deficiency, high certainty
Preventing bleeding in newborns, moderate certainty
Bone density and fractures from supplements, mixed evidence
Food vitamin K and fractures (observational), low certainty
Steadier warfarin control (supervised), low certainty
Calcium in heart arteries (MK-7) and dialysis, low certainty
Heart-risk and blood sugar markers, low certainty

Main compounds

Phylloquinone (K1)
Menaquinone-4 (MK-4)
Menaquinone-7 (MK-7)
Menadione (K3)

Common forms

Food sources (leafy greens, broccoli, Brussels sprouts, cabbage, some oils)
K1 and K2 capsules and multivitamins
Newborn injection or oral vitamin K given by a care team

Research links: 2019 review of 36 trials: vitamin K for bone density and fractures · 2000 Cochrane review: vitamin K for newborn bleeding · 2016 position paper: preventing newborn vitamin K deficiency bleeding · 2026 trial: MK-7 and coronary artery calcium (180 people) · 2016 review: dietary vitamin K and warfarin · Research Library · Genes & Biomarkers Library

What it is and its history

Accepted scientific name: Vitamin K (a family of fat-soluble vitamins: phylloquinone, K1, and menaquinones, K2)
Common names: Vitamin K (English); The clotting vitamin (English); Vitamina K (Spanish); Phylloquinone (K1) (English); Menaquinone (K2) (English)
Family or group: Fat-soluble vitamin. MedlinePlus says the body stores vitamin K in the liver and other tissues, including the brain, heart, pancreas and bone.
Look-alikes and adulterants: Name: Vitamin K1 and vitamin K2; Note: Different forms with different food sources and behaviour in the body. K1 is the main form in leafy vegetables; K2 forms (MK-4, MK-7) come from gut bacteria and some foods. There is a separate page comparing them.; Name: Vitamin D; Note: Another fat-soluble vitamin that is often sold together with vitamin K; they are different nutrients with different roles.
Sustainability and conservation: Not assessed.

What is inside, and how it may work

What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.

Main compounds

Compound	Family	Where it is concentrated	Activity studied	Level of evidence
Phylloquinone (vitamin K1)	vitamin K	Leaves (green leafy vegetables) Food content is in the Food sources benefit item (USDA).	The main form in leafy vegetables. Used in the oral trial in people on warfarin and in newborn and bone trials. ^{22 26 14}	Human data
Menaquinone-4 (MK-4, menatetrenone)	vitamin K2	USDA SR Legacy lists MK-4 for only a few foods, for example cheddar about 8.6 mcg per 100 g.	Used as an osteoporosis medicine in Japanese trials. In one small study of healthy women MK-4 was not detectable in blood after nutritional doses. ^{15 13 26}	Human data
Menaquinone-7 (MK-7)	vitamin K2	Not read from a source.	Absorbed well and detectable in blood up to 48 hours in healthy women; tested in a 3-year bone trial and a 2-year coronary calcium trial. ^{13 4 17}	Human data
Menadione (vitamin K3)	vitamin K	Not read from a source.	Named by MedlinePlus as a further form. Its safety and use were not researched for this page. ²²	Not researched

Mechanisms, receptors and pathways

Target or pathway	Gene or receptor	What was found	Level
Clotting factors	Clotting factors II, VII, IX and X (proteins made in the liver)	The liver needs vitamin K to make these proteins. Without vitamin K, blood would not clot (MedlinePlus). ²²	Human data
Bone protein activation	Osteocalcin	Vitamin K is a cofactor in the carboxylation of osteocalcin, a bone protein that binds bone mineral. K2 trials lower the undercarboxylated osteocalcin marker (meta-analyses). ^{6 15}	Human data
Blood-vessel protein activation	Matrix Gla protein (MGP)	Vitamin K supplements lowered dp-ucMGP, a blood marker of inactive MGP, in dialysis trials. Calcification scores did not change significantly. ²	Human data

Absorption, metabolism and elimination

Absorption: Vitamin K is fat-soluble. MedlinePlus says deficiency occurs when the gut cannot absorb it. In a small study of healthy Japanese women, MK-7 was well absorbed and peaked at about 6 hours, while MK-4 was not detectable in blood.
Distribution: MedlinePlus says the body stores vitamin K in the liver and other tissues including the brain, heart, pancreas and bone. The NHS says what the body does not need right away is stored in the liver.
Metabolism: Not read from a source.
Elimination: Not read from a source.
Bioavailability: MK-7 stayed in blood up to 48 hours; MK-4 at nutritional doses was not detectable (one small study). Bioavailability of K1 from foods versus pills was not compared in the sources read.

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Isolated compounds versus whole extracts

Food vitamin K and pills are not the same thing. Greens bring other nutrients and fibre, and the K1 in them is only one form. Most trials above use pills, often of K2 forms, which USDA tables barely cover for foods. Observational studies of food K1 link higher intake with fewer fractures, but trials of pills have mixed results. No trial comparing food with pills was read.

Nutritional composition

Vitamin K (phylloquinone) content of foods is from USDA FoodData Central SR Legacy (April 2018 release), read 2026-10-26 from a saved local copy; values are per 100 g and per household portion, see the Food sources benefit item. Menaquinones are mostly not listed in SR Legacy, so natto and other K2-rich foods are under-represented.

10benefits and uses looked at

26studies and sources checked

High certaintybest evidence rating found

7lab markers tracked in trials

2 high certainty1 moderate certainty1 mixed findings6 low certainty

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What was looked at

The 10 benefits and uses checked for Vitamin K, each with how strong the evidence is. Tap one to open it.

Blood clotting and vitamin K deficiencyHigh certainty
Food sources of vitamin KHigh certainty
Preventing bleeding in newbornsModerate certainty
Bone density and fractures (supplements)Mixed findings
Vitamin K from food and fractures (observational)Low certainty
Steadier control for people on warfarinLow certainty
Calcium build-up in heart arteries (MK-7)Low certainty
Vascular calcification in people on dialysisLow certainty
Heart-disease risk markers (blood fats, CRP, body measures)Low certainty
Blood sugar markers in prediabetes and type 2 diabetesLow certainty

Lab markers tracked in the studies

Time in the target INR range (warfarin)Lumbar spine bone mineral densityUndercarboxylated osteocalcin (ucOC) and the ucOC/OC ratioCoronary artery calcium (CAC) scoredp-ucMGP (inactive matrix Gla protein)HOMA-IR (insulin-resistance score)Fasting glucose and HbA1c

What is Vitamin K good for?

The main studied uses and how strong the human evidence is for each. A normal job in the body is not proof that extra pills help; each row says which.

Blood clotting and vitamin K deficiencyHigh certaintyThe liver needs vitamin K to make clotting factors II, VII, IX and X. Deficiency is very rare in adults and causes easy bruising and bleeding. Extra pills are expected to help only people who are short of it. Food sources of vitamin KHigh certaintyLeafy greens are the main source of vitamin K1: a cup of cooked kale has about 494 mcg and a cup of cooked spinach about 889 mcg (USDA). Eggs, chicken, beef and cheddar have under 1 mcg per portion. Preventing bleeding in newbornsModerate certaintyOne vitamin K injection after birth reduced bleeding in the first week in a Cochrane review, and a European position paper says all newborns should get vitamin K. This is care given by the newborn's team, not a parent's supplement choice. Bone density and fractures (supplements)Mixed findingsPooled K2 trials found slightly higher lumbar spine bone density, but the broadest review of 36 trials found no clear effect on density at most sites or on vertebral fractures and called the evidence insufficient. Vitamin K from food and fractures (observational)Low certaintyIn observational studies, people with the highest vitamin K1 intake from food had about a fifth fewer fractures (RR 0.78). This is a link, not proof of cause. Steadier control for people on warfarinLow certaintyIn one small supervised trial of 70 people with unstable warfarin control, a daily vitamin K1 supplement raised time in the target range (28% versus 15%). The NHS still says not to take vitamin K supplements on warfarin. Calcium build-up in heart arteries (MK-7)Low certaintyA 2-year trial of MK-7 in 180 people with coronary artery disease slowed the rise in coronary calcium score. The authors say the clinical meaning is not known. Vascular calcification in people on dialysisLow certaintyIn people on dialysis, vitamin K lowered a blood marker (dp-ucMGP) but did not clearly improve calcification scores or survival in 11 trials. Heart-disease risk markers (blood fats, CRP, body measures)Low certaintyA pooled analysis of 17 trials found no clear effect on blood fats, CRP or body measures; only a small drop in an insulin-resistance score. Blood sugar markers in prediabetes and type 2 diabetesLow certaintyA 2026 pooled analysis of 8 trials found small drops in fasting glucose, HbA1c and HOMA-IR in prediabetes and type 2 diabetes. The trials were few and of moderate quality.

Benefits, one by one

Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.

Blood clotting and vitamin K deficiency

High certainty

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. Real deficiency is very rare in adults. It happens when the gut cannot absorb the vitamin, or after long courses of antibiotics, and shows up as bruising and bleeding.

2 studiesVitamin K from food (mainly K1) and supplements (K1, K2 forms); forms…

Studies, doses and limits

What the trials found

MedlinePlus says the body needs vitamin K to make clotting factors, that deficiency is very rare and happens when the gut cannot absorb it or after long-term antibiotics, and that people with deficiency are often more likely to bruise and bleed. The NHS lists blood clotting and wound healing as the main jobs and says you should be able to get all you need from a varied diet, because the body stores what it does not use right away in the liver.

Results

Vitamin K is essential and a shortage causes bleeding. Extra vitamin K is expected to help only people who are short of it. Easy bruising has many causes, so it needs a doctor, not a supplement.

Effect sizes as reported

No effect sizes apply: these are nutrient roles, not trial results.

Why this rating

High that vitamin K is essential for clotting and that deficiency causes bleeding (MedlinePlus, NHS). Neither page reports trial data; they state well-known physiology.

Form and dose studied

Vitamin K from food (mainly K1) and supplements (K1, K2 forms); forms are not compared here.

Who was studied

General population. People who cannot absorb fat or who take long antibiotic courses are the groups named by MedlinePlus.

Limits

Both health pages are summaries. The NHS page's own review date (2023) has passed. The NIH Office of Dietary Supplements fact sheet could not be read.

Why researchers looked

People ask what vitamin K does and whether they get enough.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Established physiology

Vitamin K helps the liver make clotting proteins (factors II, VII, IX and X), per MedlinePlus. This is established physiology, not a trial result.

A proposed mechanism does not show that the effect happens in people.

If you take warfarin, vitamin K changes how it works; see the Safety tab.

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Food sources of vitamin K

High certainty

Vitamin K1 comes mostly from green leafy vegetables. By USDA data, 1 cup of cooked kale has about 494 micrograms (mcg), a cup of cooked spinach about 889 mcg, a cup of cooked collards about 773 mcg and half a cup of cooked broccoli about 110 mcg. Eggs, meat, fish and dairy have very little K1. Gut bacteria also make some vitamin K. USDA's tables give K1 for most foods but little on K2, so K2 amounts are not given here.

4 studiesFoods only; this is not a recommendation to eat any food or to take v…

Studies, doses and limits

What the trials found

MedlinePlus names kale, spinach, turnip greens, collards, Swiss chard, mustard greens, parsley, romaine and green leaf lettuce; Brussels sprouts, broccoli, cauliflower and cabbage; and smaller amounts in fish, liver, meat, eggs and cereals. The NHS adds vegetable oils and cereal grains. MedlinePlus also says bacteria in the lower gut make vitamin K. No trial compared food vitamin K with vitamin K pills for health results.

Results

Leafy greens carry far more K1 than other foods. A cup of cooked greens holds more than a cup of raw because cooking packs more leaf into the cup. Oils differ widely.

Effect sizes as reported

USDA vitamin K (phylloquinone), per 100 g and per portion: kale raw 389.6 mcg (about 82 mcg per cup, 21 g); kale cooked 418.5 mcg (about 494 mcg per cup, 118 g); spinach raw 482.9 mcg (about 145 mcg per cup, 30 g); spinach cooked 493.6 mcg (about 889 mcg per cup, 180 g); collards cooked 406.6 mcg (about 773 mcg per cup, 190 g); turnip greens cooked 367.6 mcg (about 529 mcg per cup, 144 g); mustard greens cooked 592.7 mcg (about 830 mcg per cup, 140 g); parsley fresh 1,640 mcg (about 62 mcg per tablespoon, 3.8 g); romaine raw 102.5 mcg (about 48 mcg per cup shredded, 47 g); broccoli cooked 141.1 mcg (about 110 mcg per half cup, 78 g); Brussels sprouts cooked 140.3 mcg (about 109 mcg per half cup, 78 g); cabbage raw 76.0 mcg (about 68 mcg per cup chopped, 89 g); cauliflower raw 15.5 mcg (about 17 mcg per cup chopped, 107 g). Oils, per 100 g and per tablespoon: soybean 183.9 mcg (about 25 mcg), canola 71.3 mcg (about 10 mcg), olive 60.2 mcg (about 8 mcg). Low sources: hard-boiled egg 0.3 mcg per 100 g (about 0.15 mcg per large egg), roasted chicken breast 0.3 mcg per 100 g, broiled 85% lean ground beef 1.2 mcg per 100 g (about 1 mcg per 3 oz), cheddar 2.4 mcg per 100 g (about 0.7 mcg per 1 oz slice). Natto lists 23.1 mcg of K1 per 100 g (about 40 mcg per cup, 175 g), but USDA SR Legacy does not list its menaquinones.

Why this rating

High that foods contain these amounts (USDA tables). How much your body absorbs from each food, and how much K2 any food holds, was not measured in the sources read.

Form and dose studied

Foods only; this is not a recommendation to eat any food or to take vitamin K.

Who was studied

General adult diet.

Limits

SR Legacy values are from a 2018 release and are mostly K1 only. Cooking, season and growing conditions change content. One cup of cooked greens can hold several times the US label reference of 120 mcg (FDA, 2024).

Why researchers looked

Many people want to know where vitamin K comes from in food and how food compares with pills.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Nutrient database

These are nutrient amounts in foods taken from USDA tables (phylloquinone, K1).

A proposed mechanism does not show that the effect happens in people.

If you take warfarin, do not change how much of these foods you eat without asking your warfarin clinic; see the Safety tab.

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Preventing bleeding in newborns

Moderate certainty

Newborn babies are born with low vitamin K and can bleed in the first weeks of life. A Cochrane review of randomised trials found that one injection of vitamin K after birth reduced bleeding in the first week. A European paediatric position paper says all newborns should get vitamin K prophylaxis. This is medical care given to babies, not a supplement choice for parents.

3 studiesVitamin K1 (phytonadione) given by injection or by mouth at birth. Th…

Studies, doses and limits

What the trials found

The Cochrane review found two randomised trials in which a single injection into muscle reduced clinical bleeding on days 1 to 7, including bleeding after circumcision, and improved clotting tests. Eleven further trials of oral schedules improved clotting tests but did not measure real bleeding. Late-onset bleeding (weeks 2 to 12) was never tested in randomised trials. The ESPGHAN position paper says all newborns should receive prophylaxis, that injection is the preferred route, and that oral schedules depend on parents and staff following the plan. A 2020 review estimated bleeding without prophylaxis at 250 to 1,700 per 100,000 births for early bleeding and 10.5 to 80 per 100,000 for late bleeding, found that oral regimens were all less effective than the injection, and reported that refusal of the injection ranged from 0% to 3.2% in US hospitals and was higher in home births and birthing centres.

Results

Vitamin K at birth prevents a rare but serious bleeding problem. The strongest trial evidence is for one injection against early (classic) bleeding; the late-bleeding evidence comes from non-randomised studies and guidance.

Effect sizes as reported

Cochrane: single injection reduced clinical bleeding on days 1 to 7 (no numbers in the abstract). Without prophylaxis: early VKDB 250 to 1,700 per 100,000 births; late VKDB 10.5 to 80 per 100,000 births (2020 review).

Why this rating

Moderate: the review is old (2000) and rests on two small trials for real bleeding, but the finding is consistent with guidance and later reviews. No GRADE rating was given in the abstract.

Form and dose studied

Vitamin K1 (phytonadione) given by injection or by mouth at birth. This page gives no amounts; the schedule is set by the newborn's care team.

Who was studied

Newborns and young infants.

Limits

Read from abstracts. Late-onset bleeding was never tested in randomised trials. Oral regimens differ and are less effective than the injection.

Why researchers looked

Vitamin K deficiency bleeding (VKDB) in babies can cause brain injury or death, so prevention has been studied.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Guideline statement

Newborns have physiologically low vitamin K levels, which can leave their clotting factors too low (ESPGHAN position paper).

A proposed mechanism does not show that the effect happens in people.

Ask your midwife or paediatrician about practice in your country. Rare severe allergic reactions have been reported with injections into a vein in adults; see the Safety tab.

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Bone density and fractures (supplements)

Mixed findings

Vitamin K helps make bone proteins work, so researchers have tested it for bone health. Results are mixed. Some pooled trials of vitamin K2 found slightly higher bone density at the lumbar spine. The broadest updated review found no clear effect on bone density at most sites or on vertebral fractures, and called the evidence too weak to say it prevents fractures.

6 studiesK2 forms (MK-4 as a Japanese osteoporosis medicine, MK-7) and K1 were…

Studies, doses and limits

What the trials found

Mott 2019 (36 randomised trials of oral vitamin K): no evidence of an effect on bone density at most sites or on vertebral fractures; clinical fractures were lower in the pooled result (OR 0.72) but not significantly lower when only low-risk-of-bias trials were counted (OR 0.76, 0.58 to 1.01); the authors call the evidence insufficient. Ma 2022 (16 trials, 6,425 post-menopausal women, vitamin K2): higher lumbar spine bone density; fractures no different overall (RR 0.96) but lower after removing one different trial (RR 0.43). Zhou 2022 (9 trials, 6,853 women with osteoporosis, K2): higher lumbar and forearm bone density. Su 2019 (18 trials, menatetrenone = MK-4 used as a medicine): slightly higher lumbar bone density, lower ucOC/OC ratio, no significant fall in vertebral fractures. A 3-year trial in 244 healthy post-menopausal women found MK-7 slowed bone loss at the lumbar spine and femoral neck, but not at the total hip. An 18-month trial in 105 women with osteoporosis already on a bone drug found no difference in bone density with K1 or MK-4.

Results

Mixed. Bone density and the vitamin K status marker improve in some pooled trials, mostly of K2 in post-menopausal women, but the broadest updated review of vitamin K trials did not find a reliable effect on density or fractures. A fracture benefit is not confirmed. Vitamin K pills are not a substitute for bone treatment that a doctor prescribes.

Effect sizes as reported

Mott 2019: clinical fracture OR 0.72 (0.55 to 0.95), low-risk trials OR 0.76 (0.58 to 1.01); vertebral fracture OR 0.96 (0.83 to 1.11); lumbar BMD at 2 years MD 1.63% (0.10 to 3.16). Ma 2022: lumbar BMD P=0.006; fracture RR 0.96, or 0.43 with one study removed. Zhou 2022: lumbar BMD WMD 2.17 (1.59 to 2.76); forearm 1.57 (1.15 to 1.99). Su 2019: lumbar BMD MD 0.05 g/cm2 (0.01 to 0.09); vertebral fracture RR 0.87 (0.64 to 1.20).

Why this rating

Mixed: pooled K2 trials favour a small bone-density gain, the broadest review calls the evidence insufficient, a recent add-on trial found nothing, and fracture results depend on which trials are counted.

Form and dose studied

K2 forms (MK-4 as a Japanese osteoporosis medicine, MK-7) and K1 were tested; they differ and results should not be carried from one to another.

Who was studied

Mostly post-menopausal women, healthy or with osteoporosis.

Limits

Different forms, amounts and bone drugs are pooled. Several reviews were read from abstracts only, and two list errata that were not read. Trial amounts are in the studies table and are not advice.

Why researchers looked

Vitamin K is needed to activate osteocalcin, a bone protein, and many women worry about bone loss after menopause.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Established physiology and human marker

Vitamin K is a cofactor in the carboxylation of osteocalcin, a protein that binds bone mineral (stated in the 2022 meta-analysis). Trials track this with the undercarboxylated-to-carboxylated osteocalcin ratio. That is a marker of vitamin K status, not proof of stronger bone.

A proposed mechanism does not show that the effect happens in people.

Adverse reactions were reported slightly more often with K2 in two meta-analyses (RR 1.33 and 1.47); serious events were not. If you take warfarin, do not start vitamin K supplements.

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Vitamin K from food and fractures (observational)

Low certainty

In large population studies, people who ate the most vitamin K1 had about a fifth fewer fractures than people who ate the least. This does not prove that vitamin K caused the difference, because people who eat plenty of greens differ in other ways.

1 studiesFood vitamin K1 only.

Studies, doses and limits

What the trials found

A 2017 meta-analysis of 4 cohort studies and 1 nested case-control study (1,114 fractures among 80,982 people) compared the highest with the lowest dietary vitamin K1 intake: RR 0.78 (0.56 to 0.99). Per 50 mcg more a day the RR was 0.97 (0.95 to 0.99). In studies with more than 10 years of follow-up the RR was 0.76 (0.58 to 0.93). All studies measured K1 only.

Results

A modest link between more K1 from food and fewer fractures, from observational studies. It may reflect a generally healthy diet.

Effect sizes as reported

Highest vs lowest intake RR 0.78 (0.56 to 0.99), I2 59.2%; per 50 mcg a day RR 0.97 (0.95 to 0.99); over 10 years RR 0.76 (0.58 to 0.93).

Why this rating

Low: observational studies with moderate differences between studies (I2 59%); confounding by a healthy diet is likely.

Form and dose studied

Food vitamin K1 only.

Who was studied

Adults in cohort studies.

Limits

Only 5 studies. K2 was not measured. The authors say higher intake 'may moderately decrease' risk, which is a hypothesis.

Why researchers looked

Researchers wanted to know whether the K1 people usually eat is linked to bone breaks.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Observational

Not established. The authors point to vitamin K's role in bone proteins; the studies cannot test that.

A proposed mechanism does not show that the effect happens in people.

If you take warfarin, do not change your leafy greens without asking your warfarin clinic.

Steadier control for people on warfarin

Low certainty

Warfarin is a blood thinner that works against vitamin K. In one small UK trial of 70 people whose warfarin control was unstable for no clear reason, a small daily vitamin K1 supplement, given under clinic supervision, improved how often their blood tests stayed in the target range. This is not something to try on your own.

3 studiesOral vitamin K1 (phylloquinone) under clinical supervision.

Studies, doses and limits

What the trials found

In a 6-month double-blind trial (Sconce 2007), 70 people on warfarin with unstable control took 150 mcg of oral vitamin K or placebo. Time within the target INR range rose by 28% on vitamin K versus 15% on placebo (P<.01), and variability in INR fell more (-0.24 vs -0.11, P<.001). A 2016 systematic review of dietary studies found mixed results and concluded that the evidence does not support cutting leafy vegetables; stable eating habits matter more.

Results

A small, single-centre trial showing steadier control in a narrow group under supervision. The NHS still says not to take vitamin K supplements while on warfarin.

Effect sizes as reported

Time in range +28% +/- 20% vs +15% +/- 20% (P<.01); INR SD -0.24 +/- 0.14 vs -0.11 +/- 0.18 (P<.001); improvement in 33 of 35 vs 24 of 33.

Why this rating

Low: one small trial, 6 months, a specific group, with no outcome such as bleeding or clots. The dietary review found mixed evidence.

Form and dose studied

Oral vitamin K1 (phylloquinone) under clinical supervision.

Who was studied

Adults on warfarin with unexplained unstable control.

Limits

Not a basis for self-treatment. Trial amounts are in the studies table, not advice.

Why researchers looked

People with unstable warfarin control tend to eat less vitamin K; the researchers tested whether a steady small supplement would smooth things out.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Hypothesis

The authors suggest the supplement works by reducing day-to-day swings in vitamin K intake. This was not tested directly.

A proposed mechanism does not show that the effect happens in people.

Never start or stop vitamin K while on warfarin without your warfarin clinic.

^{14 16 24}

Calcium build-up in heart arteries (MK-7)

Low certainty

One 2-year randomised trial in 180 people with symptomatic coronary artery disease found that menaquinone-7 (MK-7) slowed the rise in coronary calcium score compared with placebo. The authors say the clinical meaning is not known. The trial did not measure heart attacks or deaths.

1 studiesMK-7 (menaquinone-7) capsules for 2 years; results should not be carr…

Studies, doses and limits

What the trials found

VitaK-CAC trial (Vossen 2026, JAMA Cardiology): 180 randomised, 85 on MK-7 analysed and 82 on placebo, 2 years. Median CAC score went from 145 to 214 AU on placebo and from 135 to 184 AU on MK-7 (P=.02). Blood MK-7 rose from 0.50 to 6.56 mcg/L. No significant adverse effects were seen. The trial studied one form (MK-7) in a specific group.

Results

A promising scan result from one trial. Not proof of fewer heart attacks, and not a reason to treat vitamin K as a heart medicine.

Effect sizes as reported

CAC score (median AU) at baseline, 1 year, 2 years: placebo 145, 173, 214; MK-7 135, 150, 184; P=.02 between groups.

Why this rating

Low: a single randomised trial of one form, a scan marker rather than heart events, and the authors themselves say the clinical significance is unknown.

Form and dose studied

MK-7 (menaquinone-7) capsules for 2 years; results should not be carried to K1 or other K2 forms.

Who was studied

People with symptoms of coronary artery disease and a CAC score of 50 to 400 AU, in the Netherlands.

Limits

One trial; funding not shown in the abstract; the plaque benefit is a CT marker. Trial amounts are in the studies table, not advice.

Why researchers looked

Vitamin K activates a protein that helps stop calcium from collecting in artery walls (matrix Gla protein), so researchers tested whether it slows artery calcification.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Human marker

Not established in people. The 2026 trial reports that MK-7 raised blood MK-7 levels and slowed calcification of non-calcified plaques; whether this makes plaque safer is described as unknown.

A proposed mechanism does not show that the effect happens in people.

If you take warfarin, do not start vitamin K supplements. See the Safety tab.

¹⁷

Vascular calcification in people on dialysis

Low certainty

People on dialysis often have calcified arteries and low vitamin K. A pooled analysis of 11 trials (830 people) found vitamin K raised blood vitamin K and lowered a calcification marker (dp-ucMGP) but did not clearly improve calcification scores or survival. It is studied only under medical care.

1 studiesK1 and K2 forms were pooled; K1 lowered the marker more.

Studies, doses and limits

What the trials found

Andrian 2023: 11 randomised trials, 830 people (adults and children, mostly on haemodialysis). Vitamin K had no effect on death. dp-ucMGP fell more with K1 (SMD -1.64, -2.05 to -1.23) than with K2 (SMD -0.56, -0.82 to -0.31). Calcification scores did not change significantly (SMD -0.14, -0.37 to 0.09). The authors judged vitamin K safe and asked for bigger trials. They note some concern about bias.

Results

Vitamin K changes the blood marker but, so far, has not been shown to reverse calcification or help people live longer on dialysis.

Effect sizes as reported

Death: no effect. dp-ucMGP: K1 SMD -1.64, K2 SMD -0.56. Calcification scores SMD -0.14 (-0.37 to 0.09), not significant.

Why this rating

Low: pooled small trials with bias concerns, and the clinical outcomes (calcification, death) showed no clear benefit.

Form and dose studied

K1 and K2 forms were pooled; K1 lowered the marker more.

Who was studied

People on dialysis (kidney failure).

Limits

Only people on dialysis. Read from the abstract. A calcification marker is not a clinical outcome.

Why researchers looked

Kidney disease is linked with artery calcification and low vitamin K, so vitamin K has been tested as a way to slow it.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Human marker

Vitamin K is needed to activate matrix Gla protein (MGP). The blood marker dp-ucMGP (inactive MGP) falls when vitamin K is given. A lower marker is not the same as less calcium in arteries.

A proposed mechanism does not show that the effect happens in people.

People with kidney disease or on dialysis should not add vitamin K without their kidney team.

Heart-disease risk markers (blood fats, CRP, body measures)

Low certainty

A pooled analysis of 17 randomised trials found that vitamin K supplements did not change body measures, inflammation (CRP), blood sugar or blood fats. The only change was a small drop in an insulin-resistance score.

1 studiesK1 and K2 supplements pooled.

Studies, doses and limits

What the trials found

Zhao 2024: 17 randomised trials. Vitamin K lowered HOMA-IR (WMD -0.24, -0.49 to -0.02, P=0.047) and had no significant effect on anthropometrics, CRP, glucose metabolism or blood-fat profile. The HOMA-IR effect was bigger with K2 than K1.

Results

No reliable change in common heart-risk markers. One barely significant result among many outcomes.

Effect sizes as reported

HOMA-IR WMD -0.24 (-0.49 to -0.02); other outcomes not significant.

Why this rating

Low: mostly null results, one borderline finding, mixed forms and groups.

Form and dose studied

K1 and K2 supplements pooled.

Who was studied

Adults in randomised trials.

Limits

Read from the abstract. Marker changes only.

Why researchers looked

If vitamin K helps arteries, it might also change common heart-risk markers.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Unknown

Not established. No mechanism for these markers was tested in the abstract.

A proposed mechanism does not show that the effect happens in people.

No safety signal in the abstract.

¹⁸

Blood sugar markers in prediabetes and type 2 diabetes

Low certainty

A 2026 pooled analysis of 8 trials in people with prediabetes or type 2 diabetes found small drops in fasting glucose, HbA1c and an insulin-resistance score with vitamin K, but no change in insulin. The trials were few and of moderate quality.

2 studiesK1 and K2 pooled.

Studies, doses and limits

What the trials found

Ahmed 2026: 8 randomised trials. Fasting glucose SMD -0.22 (-0.39 to -0.05), HbA1c MD -1.00% (-1.92 to -0.07), HOMA-IR MD -0.63 (-1.20 to -0.06); no effect on insulin or HOMA-beta. Low doses of K2 and K1 were linked to a lower HbA1c and HOMA-IR respectively; shorter interventions (under 12 weeks) were linked to lower HOMA-IR.

Results

Small lab-marker improvements in a few moderate-quality trials. Not proof of better diabetes control.

Effect sizes as reported

Fasting glucose SMD -0.22 (-0.39 to -0.05); HbA1c MD -1.00% (-1.92 to -0.07); HOMA-IR MD -0.63 (-1.20 to -0.06).

Why this rating

Low: only 8 trials, moderate quality, wide intervals, markers rather than outcomes.

Form and dose studied

K1 and K2 pooled.

Who was studied

Adults with prediabetes or type 2 diabetes.

Limits

Read from the abstract. The HbA1c range is wide (-1.92 to -0.07).

Why researchers looked

Lab studies suggested vitamin K may affect how the body handles sugar; the pooled analysis tested this in people.

Traditional use

Vitamin K is an essential nutrient. Its roles are well established; that is different from showing that extra pills treat a condition.

Proposed mechanism Preclinical hypothesis

Not established. The authors call earlier lab findings promising but note scant clinical evidence.

A proposed mechanism does not show that the effect happens in people.

People on diabetes medicines should not add supplements without asking their doctor.

^{1 18}

Connections to the rest of health

How Vitamin K connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.

Explore every connection: goals, body systems, organs, symptoms, genes

Kind of connection Connected to Search

A. Wellness goals

Connected to	Kind of connection	Evidence status	Context	Studies
Balanced Nutrition		High certainty	Blood clotting and vitamin K deficiency: 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. Real deficiency is very rare in adults. It happens when the gut cannot absorb the vitamin, or after long courses of antibiotics, and shows up as bruising and bleeding.	^{22 23}
Preventive Wellness		High certainty	Blood clotting and vitamin K deficiency: 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. Real deficiency is very rare in adults. It happens when the gut cannot absorb the vitamin, or after long courses of antibiotics, and shows up as bruising and bleeding.	^{22 23}
Balanced Nutrition		High certainty	Food sources of vitamin K: Vitamin K1 comes mostly from green leafy vegetables. By USDA data, 1 cup of cooked kale has about 494 micrograms (mcg), a cup of cooked spinach about 889 mcg, a cup of cooked collards about 773 mcg and half a cup of cooked broccoli about 110 mcg. Eggs, meat, fish and dairy have very little K1. Gut bacteria also make some vitamin K. USDA's tables give K1 for most foods but little on K2, so K2 amounts are not given here.	^{26 22 23 21}
Preventive Wellness	Demonstrated clinical effect	Moderate certainty	Preventing bleeding in newborns: Newborn babies are born with low vitamin K and can bleed in the first weeks of life. A Cochrane review of randomised trials found that one injection of vitamin K after birth reduced bleeding in the first week. A European paediatric position paper says all newborns should get vitamin K prophylaxis. This is medical care given to babies, not a supplement choice for parents.	^{11 8 5}
Bone Health		Mixed findings	Bone density and fractures (supplements): Vitamin K helps make bone proteins work, so researchers have tested it for bone health. Results are mixed. Some pooled trials of vitamin K2 found slightly higher bone density at the lumbar spine. The broadest updated review found no clear effect on bone density at most sites or on vertebral fractures, and called the evidence too weak to say it prevents fractures.	^{10 6 19 15 4 9}
Healthy Aging		Mixed findings	Bone density and fractures (supplements): Vitamin K helps make bone proteins work, so researchers have tested it for bone health. Results are mixed. Some pooled trials of vitamin K2 found slightly higher bone density at the lumbar spine. The broadest updated review found no clear effect on bone density at most sites or on vertebral fractures, and called the evidence too weak to say it prevents fractures.	^{10 6 19 15 4 9}
Bone Health		Low certainty	Vitamin K from food and fractures (observational): In large population studies, people who ate the most vitamin K1 had about a fifth fewer fractures than people who ate the least. This does not prove that vitamin K caused the difference, because people who eat plenty of greens differ in other ways.	³
Heart Health		Low certainty	Steadier control for people on warfarin: Warfarin is a blood thinner that works against vitamin K. In one small UK trial of 70 people whose warfarin control was unstable for no clear reason, a small daily vitamin K1 supplement, given under clinic supervision, improved how often their blood tests stayed in the target range. This is not something to try on your own. Calcium build-up in heart arteries (MK-7): One 2-year randomised trial in 180 people with symptomatic coronary artery disease found that menaquinone-7 (MK-7) slowed the rise in coronary calcium score compared with placebo. The authors say the clinical meaning is not known. The trial did not measure heart attacks or deaths.	^{14 16 24 17}
Heart Health		Low certainty	Vascular calcification in people on dialysis: People on dialysis often have calcified arteries and low vitamin K. A pooled analysis of 11 trials (830 people) found vitamin K raised blood vitamin K and lowered a calcification marker (dp-ucMGP) but did not clearly improve calcification scores or survival. It is studied only under medical care.	²
Heart Health		Low certainty	Heart-disease risk markers (blood fats, CRP, body measures): A pooled analysis of 17 randomised trials found that vitamin K supplements did not change body measures, inflammation (CRP), blood sugar or blood fats. The only change was a small drop in an insulin-resistance score.	¹⁸
Cholesterol Balance		Low certainty	Heart-disease risk markers (blood fats, CRP, body measures): A pooled analysis of 17 randomised trials found that vitamin K supplements did not change body measures, inflammation (CRP), blood sugar or blood fats. The only change was a small drop in an insulin-resistance score.	¹⁸
Metabolic Health		Low certainty	Heart-disease risk markers (blood fats, CRP, body measures): A pooled analysis of 17 randomised trials found that vitamin K supplements did not change body measures, inflammation (CRP), blood sugar or blood fats. The only change was a small drop in an insulin-resistance score.	¹⁸
Blood Sugar Balance		Low certainty	Blood sugar markers in prediabetes and type 2 diabetes: A 2026 pooled analysis of 8 trials in people with prediabetes or type 2 diabetes found small drops in fasting glucose, HbA1c and an insulin-resistance score with vitamin K, but no change in insulin. The trials were few and of moderate quality.	^{1 18}
Metabolic Health		Low certainty	Blood sugar markers in prediabetes and type 2 diabetes: A 2026 pooled analysis of 8 trials in people with prediabetes or type 2 diabetes found small drops in fasting glucose, HbA1c and an insulin-resistance score with vitamin K, but no change in insulin. The trials were few and of moderate quality.	^{1 18}

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Blood	Biological association	High certainty	Studied for: Blood clotting and vitamin K deficiency Studied for: Preventing bleeding in newborns	^{22 23 11 8 5 14 16 24}
Digestive System	Biological association	High certainty	Studied for: Blood clotting and vitamin K deficiency Studied for: Food sources of vitamin K	^{22 23 26 21}
Nutrition	Biological association	High certainty	Studied for: Food sources of vitamin K	^{26 22 23 21}
Musculoskeletal System	Biological association	Mixed findings	Studied for: Bone density and fractures (supplements) Studied for: Vitamin K from food and fractures (observational)	^{10 6 19 15 4 9 3}
Cardiovascular System	Biological association	Low certainty	Studied for: Steadier control for people on warfarin Studied for: Calcium build-up in heart arteries (MK-7)	^{14 16 24 17 2 18}
Kidney Urinary	Biological association	Low certainty	Studied for: Vascular calcification in people on dialysis	²
Metabolic System	Biological association	Low certainty	Studied for: Heart-disease risk markers (blood fats, CRP, body measures)	¹⁸
Blood Sugar Support	Biological association	Low certainty	Studied for: Blood sugar markers in prediabetes and type 2 diabetes	^{1 18}
Endocrine System	Biological association	Low certainty	Studied for: Blood sugar markers in prediabetes and type 2 diabetes	^{1 18}

E. Health conditions

Connected to	Evidence status	Context	Studies
Vitamin K deficiency bleeding in newborns	Demonstrated clinical effect	Prophylaxis at birth prevents classic bleeding; injection is preferred. Vitamin K at birth prevents classic bleeding; injection is the preferred route. Preparation or compound: Vitamin K1 at birth	^{11 8 5}
Osteoporosis	Preliminary	Results on bone density and fractures are mixed; the broadest review calls the evidence insufficient. Preparation or compound: Vitamin K1, MK-4, MK-7	^{10 6 19}
Coronary artery calcification	Preliminary	One 2-year MK-7 trial slowed calcium score progression; clinical meaning unknown. Preparation or compound: MK-7	¹⁷

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
Time in the target INR range (warfarin)	Biological association	Low certainty	Measured in trials: higher time in range in one small trial. A lab change is not the same as a health benefit.	¹⁴
Lumbar spine bone mineral density	Biological association	Mixed findings	Measured in trials: slightly higher in several pooled trials; no gain in one add-on trial. A lab change is not the same as a health benefit.	^{10 19 9}
Undercarboxylated osteocalcin (ucOC) and the ucOC/OC ratio	Biological association	Moderate certainty	Measured in trials: lower with vitamin K2. A lab change is not the same as a health benefit.	^{6 15}
Coronary artery calcium (CAC) score	Biological association	Low certainty	Measured in trials: rose less on MK-7 in one trial. A lab change is not the same as a health benefit.	¹⁷
dp-ucMGP (inactive matrix Gla protein)	Biological association	Moderate certainty	Measured in trials: lower with vitamin K. A lab change is not the same as a health benefit.	²
HOMA-IR (insulin-resistance score)	Biological association	Low certainty	Measured in trials: slightly lower. A lab change is not the same as a health benefit.	^{18 1}
Fasting glucose and HbA1c	Biological association	Low certainty	Measured in trials: lower in prediabetes and type 2 diabetes trials. A lab change is not the same as a health benefit.	¹

K. Biological pathways

Connected to	Kind of connection	Evidence status	Context	Studies
Osteocalcin	Preliminary mechanism	Human	Bone protein that vitamin K activates; its undercarboxylated form is used as a vitamin K status marker.	^{6 15}
Matrix Gla protein (MGP)	Preliminary mechanism	Human	Blood-vessel protein that vitamin K activates; dp-ucMGP is used as a marker in dialysis trials.	²

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
Phylloquinone (vitamin K1)	Biological association	Human	The main form in leafy vegetables. Used in the oral trial in people on warfarin and in newborn and bone trials. Preparation or compound: Leaves (green leafy vegetables)	^{22 26 14}
Menaquinone-4 (MK-4, menatetrenone)	Biological association	Human	Used as an osteoporosis medicine in Japanese trials. In one small study of healthy women MK-4 was not detectable in blood after nutritional doses.	^{15 13 26}
Menaquinone-7 (MK-7)	Biological association	Human	Absorbed well and detectable in blood up to 48 hours in healthy women; tested in a 3-year bone trial and a 2-year coronary calcium trial.	^{13 4 17}
Menadione (vitamin K3)	Biological association	Not researched	Named by MedlinePlus as a further form. Its safety and use were not researched for this page.	²²

Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).

Evidence at a glance: what the research found for 10 outcomes

2High certainty

1Moderate certainty

6Low certainty

1Mixed findings

Each outcome below is one thing researchers measured. Certainty is how far the evidence can be trusted, not how well it works. The full studies are on the next tab.

Blood clotting and vitamin K deficiency 2 studies High certainty Food sources of vitamin K 4 studies High certainty Preventing bleeding in newborns 3 studies Moderate certainty Bone density and fractures (supplements) 6 studies Mixed findings Vitamin K from food and fractures (observational) 1 study Low certainty Steadier control for people on warfarin 3 studies Low certainty Calcium build-up in heart arteries (MK-7) 1 study Low certainty Vascular calcification in people on dialysis 1 study Low certainty Heart-disease risk markers (blood fats, CRP, body measures) 1 study Low certainty Blood sugar markers in prediabetes and type 2 diabetes 2 studies Low certainty

The evidence

The research centre for Vitamin K. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.

Evidence by outcome

Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).

How we rate evidence

High certainty

Several well-run trials or reviews agree; further research is unlikely to change the picture much.

Moderate certainty

Good trials point the same way, but some doubt remains.

Low certainty

Small, short or inconsistent trials. The finding could change with better research.

Very low certainty

Very little or very weak human data. Treat as a possibility only.

Mixed findings

Trials or reviews disagree with each other.

Not enough evidence

Not enough human research to say either way.

Evidence against

Good research found no benefit, or found harm.

We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our existing vitamin K summary, read the MedlinePlus, NHS, FDA and EFSA pages, re-checked food values in saved US Department of Agriculture data, and re-read PubMed abstracts for reviews, trials and guidance. Only abstracts were read for studies. The NIH Office of Dietary Supplements page was blocked and is marked unread.

Study library: every study we checked 26

Design Research type Year from Search

Study	Design	People	Product, dose, length	Result
Ahmed 2026 The Differential Effects of Vitamin K Across Glycaemic Outcomes in Prediabetes and Type 2 Diabetes Mellitus. Nutrients · PMID 41599883 · DOI	Systematic review meta analysis	8 randomised trials in people with prediabetes or type 2 diabetes	Vitamin K1 and K2 Oral Differs by trial Some under 12 weeks · vs Control groups	Vitamin K was linked to lower fasting glucose, HbA1c and HOMA-IR, with no change in insulin or beta-cell function. The authors say the few moderate-quality trials call for larger, longer trials. Fasting glucose SMD -0.22; HbA1c MD -1.00%; HOMA-IR MD -0.63 (Fasting glucose -0.22 (-0.39 to -0.05); HbA1c -1.00 (-1.92 to -0.07); HOMA-IR -0.63 (-1.20 to -0.06)) Methods, limits and funding Outcomes: Fasting glucose, HbA1c, HOMA-IR, insulin, HOMA-beta Limitations: Only 8 trials, moderate quality, wide intervals. Marker changes only. Funding and conflicts: Authors declare no conflict of interest. Read: abstract
Andrian 2023 Vitamin K supplementation impact in dialysis patients: a systematic review and meta-analysis of randomized trials. Clin Kidney J · PMID 38046003 · DOI	Systematic review meta analysis	830 11 randomised trials, 830 people on dialysis (adults and children, mostly haemodialysis)	Vitamin K1 or K2 against lower doses, standard care or placebo Oral Differs by trial Differs by trial · vs Lower dose, standard care or placebo	Vitamin K had no effect on death. It raised vitamin K levels and lowered dp-ucMGP, a blood marker. It did not show a clear benefit on calcification scores (SMD -0.14, not significant). K1 lowered dp-ucMGP more than K2. The authors call vitamin K safe and say bigger, better trials are needed. Death: no effect; dp-ucMGP lowered (K1 SMD -1.64; K2 SMD -0.56); calcification scores SMD -0.14 (K1 -1.64 (-2.05 to -1.23); K2 -0.56 (-0.82 to -0.31); calcification scores -0.14 (-0.37 to 0.09)) Methods, limits and funding Outcomes: Death; blood vitamin K; dp-ucMGP (a calcification marker); calcification scores Limitations: The authors note concerns about bias. Only people on dialysis. Funding and conflicts: Authors declare no conflict of interest. Read: abstract
Hao 2017 Vitamin K intake and the risk of fractures: A meta-analysis. Medicine (Baltimore) · PMID 28445289 · DOI	Meta analysis observational	80982 4 cohort studies and 1 nested case-control study; 1,114 fractures among 80,982 people	Dietary vitamin K1 (phylloquinone) from food Food More than 10 years in the longest studies · vs Lowest versus highest intake group	People with the highest food vitamin K1 intake had about a fifth fewer fractures than people with the lowest. The link was clearer in studies with more than 10 years of follow-up. This is a link in observational studies, so it does not show that vitamin K caused the difference. Highest vs lowest intake RR 0.78; per 50 micrograms a day RR 0.97; over 10 years follow-up RR 0.76 (Highest vs lowest RR 0.78 (0.56 to 0.99), I2 59.2%; per 50 micrograms RR 0.97 (0.95 to 0.99); over 10 years RR 0.76 (0.58 to 0.93)) Methods, limits and funding Outcomes: Fracture risk Limitations: Observational. People who eat many greens differ in other ways. All studies measured K1 only. Results varied between studies (I2 59%). Funding and conflicts: Authors declare no conflict of interest. Read: abstract
Knapen 2013 Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int · PMID 23525894 · DOI	Randomised controlled trial	244 244 healthy post-menopausal women	Menaquinone-7 (MK-7) capsules Capsules 180 micrograms a day (trial amount, not advice) 3 years · vs Placebo	MK-7 improved vitamin K status and slowed the age-related fall in bone density at the lumbar spine and femoral neck, but not at the total hip. Bone strength indices and loss of vertebral height at one level were also better. The abstract gives no numbers for the size of the effect. No numbers in the abstract (Not given in the abstract) Methods, limits and funding Outcomes: Bone mineral density at spine, hip and femoral neck; bone strength; vertebral height; vitamin K status marker Limitations: Healthy women only, one form (MK-7). No effect size in the abstract and fractures were not the main outcome. Funding and conflicts: Funding is not stated in the abstract; manufacturer links were not checked. Read: abstract
Loyal 2020 Refusal of Intramuscular Vitamin K by Parents of Newborns: A Review. Hosp Pediatr · PMID 32019806 · DOI	Narrative review	Review of studies of parents who refused the newborn vitamin K injection, and of babies who did not get vitamin K	Vitamin K to newborns (injection or oral) Injection or oral · vs Babies who did and did not receive vitamin K	Without prophylaxis, vitamin K deficiency bleeding was estimated at 250 to 1,700 per 100,000 births for early bleeding and 10.5 to 80 per 100,000 for late bleeding. Refusal of the injection ranged from 0% to 3.2% in US hospitals, up to 14.5% in home births and up to 31.0% in birthing centres. Oral regimens varied and all were less effective than the injection. The bleeding is rare but can cause brain injury or death. Early VKDB 250 to 1,700 per 100,000 births; late VKDB 10.5 to 80 per 100,000 births (without prophylaxis) (Not applicable) Methods, limits and funding Outcomes: How often vitamin K is refused; how often bleeding (VKDB) happens without it Limitations: A narrative review read from the abstract. Rates come from different studies and places. Funding and conflicts: Supported by US National Institutes of Health grants (listed); no conflict of interest disclosed. Read: abstract
Ma 2022 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 · PMID 36033779 · DOI	Systematic review meta analysis	6425 16 randomised trials, 6,425 post-menopausal women	Vitamin K2 (forms pooled), alone or with other bone treatments Oral supplement Amounts differ between trials Not given in the abstract · vs Control groups (placebo or other treatment)	Vitamin K2 improved lumbar spine bone density in 10 trials. Fracture numbers were no different overall (RR 0.96); after one very different trial was removed, fractures were lower (RR 0.43). Vitamin K2 lowered a blood marker of vitamin K status (undercarboxylated osteocalcin). Adverse reactions were no different from control. Fractures RR 0.96 (all trials); RR 0.43 after removing one study; adverse reactions RR 1.03 (Fractures P=0.65 (all), P=0.01 (one study removed); adverse reactions RR 1.03 (0.87 to 1.21); BMD result P=0.006) Methods, limits and funding Outcomes: Lumbar spine BMD; fractures; undercarboxylated osteocalcin; adverse reactions Limitations: The strong fracture result appeared only after one trial was dropped. Trials differ in form, amount and bone treatments given together. Funding and conflicts: Authors declare no commercial or financial conflict. Read: abstract
Mar 2022 Drug Interactions Affecting Oral Anticoagulant Use. Circ Arrhythm Electrophysiol · PMID 35622425 · DOI	Narrative review	Review of drug interactions with warfarin and direct oral anticoagulants	Warfarin and direct oral anticoagulants (DOACs)	The review says warfarin interactions come mainly from drugs acting on liver enzymes (CYP2C9 and others) and that DOACs are mainly affected by drugs acting on P-gp and, less, CYP3A4. The abstract does not mention vitamin K in either list. No numbers (Not applicable) Methods, limits and funding Outcomes: Drug-drug interactions with blood thinners Limitations: A review of drug-drug interactions, read from the abstract only. Not mentioning vitamin K does not show that vitamin K has no effect. Funding and conflicts: Supported by US NIH grants (listed); no conflict listed in the record. Read: abstract
Mihatsch 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 · DOI	Practice guideline	Healthy term newborns and young infants (guidance paper)	Vitamin K1 prophylaxis (injection or oral schedules) Injection or oral The paper sets out injection and oral schedules; amounts are not repeated on this page At birth, with follow-up oral doses in some schedules	All newborn infants should receive vitamin K prophylaxis, and the date, dose and route should be written down. Injection into muscle is the preferred route. Oral schedules depend on parents and staff following the plan, and the oral route is not suitable for preterm babies or babies with liver or gut absorption problems. Guidance, not a trial (Not applicable) Methods, limits and funding Outcomes: Prevention of vitamin K deficiency bleeding Limitations: A position paper from a paediatric nutrition committee, read from the abstract only. It is guidance, not new trial data. Funding and conflicts: Committee paper; no conflict of interest listed in the record. Read: abstract
Moore 2023 The additive effect of vitamin K supplementation and bisphosphonate on fracture risk in post-menopausal osteoporosis: a randomised placebo controlled trial. Arch Osteoporos · PMID 37338608 · DOI	Randomised controlled trial	105 105 post-menopausal women (average age 68.7) with osteoporosis and low blood vitamin K1, already taking a bone drug (bisphosphonate) and calcium and/or vitamin D	Vitamin K1 or MK-4 added to usual bone treatment Capsules K1 1 mg a day or MK-4 45 mg a day (trial amounts, not advice) 18 months · vs Placebo	Bone density and bone turnover markers did not differ from placebo with either K1 or MK-4. After adjustment, a few hip-shape measures differed with K1 (p about 0.03 to 0.04). The authors call this a modest effect needing confirmation. BMD and turnover markers: no significant difference (Not given for BMD in the abstract) Methods, limits and funding Outcomes: Bone density at hip and spine; hip shape measures; bone turnover markers Limitations: Small trial. The few positive hip-shape findings came from a per-protocol analysis and may be chance. Funding and conflicts: Authors declare no conflicts for most; two authors report speaker fees and advisory roles for vitamin D and osteoporosis treatments (stated in the record). Registration: NCT01232647 Read: abstract
Mott 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 · DOI	Systematic review meta analysis	36 randomised trials of oral vitamin K in adults, mostly post-menopausal women or people with osteoporosis	Oral vitamin K (K1 and K2 forms pooled) Capsules or tablets Amounts differ between trials 6 months to 2 years or more in the BMD analyses · vs Placebo or no vitamin K	For post-menopausal or osteoporotic people there was no evidence that vitamin K changes bone density at most sites or vertebral fractures. Clinical fractures were lower in the pooled result, but the result was weaker when only low-risk-of-bias trials were used. The authors call the evidence insufficient to confirm a benefit. Any clinical fracture OR 0.72; low-risk-of-bias trials only OR 0.76; vertebral fracture OR 0.96; lumbar spine BMD +1.63% at 2 years (Clinical fracture OR 0.72 (0.55 to 0.95); low-risk trials OR 0.76 (0.58 to 1.01); vertebral fracture OR 0.96 (0.83 to 1.11); lumbar BMD at 2 years MD 1.63% (0.10 to 3.16)) Methods, limits and funding Outcomes: Bone mineral density (BMD); clinical fractures; vertebral fractures Limitations: Results got smaller and non-significant when high-risk-of-bias trials were removed. The record lists an erratum for this paper that was not read. Funding and conflicts: No conflict of interest listed; funding not stated in the abstract. Read: abstract
Puckett 2000 Prophylactic vitamin K for vitamin K deficiency bleeding in neonates. Cochrane Database Syst Rev · PMID 11034761 · DOI	Systematic review	Newborn babies; 2 randomised trials of a single injection versus placebo or nothing, and 11 trials of oral versus other schedules	Vitamin K1 (phytonadione) given after birth Injection into muscle or by mouth Reviewers conclude a single 1.0 mg injection is effective (amount stated by the reviewers) Single dose, or 3 oral doses · vs Placebo, no treatment, or another route	One injection after birth reduced clinical bleeding on days 1 to 7, including bleeding after circumcision, and improved clotting tests. Oral doses also improved clotting tests but were not tested for real bleeding. Neither route was tested in randomised trials for late bleeding (weeks 2 to 12). Reduced clinical bleeding at 1 to 7 days (no numbers in the abstract) (Not given in the abstract) Methods, limits and funding Outcomes: Bleeding in the first weeks of life (classic and late); blood-clotting tests; plasma vitamin K Limitations: An older review (2000). Only two small trials measured real bleeding. Late-onset bleeding was never tested in randomised trials. Funding and conflicts: Cochrane review; no conflict of interest listed in the record. Read: abstract
Riegert-Johnson 2002 The incidence of anaphylaxis following intravenous phytonadione (vitamin K1): a 5-year retrospective review. Ann Allergy Asthma Immunol · PMID 12392385 · DOI	Retrospective review	6572 6,572 intravenous doses at one large US hospital over 58 months, plus 14 cases found in the literature	Intravenous phytonadione (vitamin K1) given as a medicine Injection into a vein 58 months of records	Two cases of anaphylaxis were found, about 3 per 10,000 doses. The reaction is thought to come from the solvent in the injection (polyethoxylated castor oil), not from vitamin K itself. The authors did not recommend routine pre-treatment with antihistamines or steroids. About 3 per 10,000 injections (0.04 to 11 per 10,000 doses) Methods, limits and funding Outcomes: Anaphylaxis (severe allergic reaction) Limitations: One hospital; only 2 events, so the range is wide. This is about the injected medicine, not oral supplements. Funding and conflicts: No conflict of interest listed. Read: abstract
Sato 2012 Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutr J · PMID 23140417 · DOI	Randomised controlled trial	Healthy Japanese women (number not given in the abstract)	Menaquinone-4 (MK-4) and menaquinone-7 (MK-7) Capsules with breakfast Single dose of 420 micrograms, then 60 micrograms a day for 7 days (trial amounts, not advice) Single dose, then 7 days · vs MK-4 versus MK-7	MK-7 was well absorbed, peaked at about 6 hours and was still detectable at 48 hours. MK-4 was not detectable in blood at any time, and 7 days of MK-4 did not raise blood MK-4. MK-7 did. The authors conclude that MK-4 in food does not contribute to vitamin K status measured in blood. MK-4 not detectable in blood; MK-7 detected up to 48 hours (Not applicable) Methods, limits and funding Outcomes: Blood levels of MK-4 and MK-7 Limitations: Blood levels only, not health outcomes; healthy women only. Funding and conflicts: No conflict of interest listed; funding not stated in the abstract. Read: abstract
Sconce 2007 Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin. Blood · PMID 17110451 · DOI	Randomised controlled trial	70 70 people on warfarin with unstable control (INR) for no clear reason (UK)	Oral vitamin K (phylloquinone, K1) Oral 150 micrograms a day (trial amount, not advice; given under clinical supervision) 6 months · vs Placebo	Vitamin K gave a bigger fall in INR variability than placebo and a bigger rise in time in the target range (28% versus 15%). Control improved in 33 of 35 on vitamin K and 24 of 33 on placebo. The authors think the benefit may come from smoothing out day-to-day changes in vitamin K intake. INR SD change -0.24 vs -0.11; time in range +28% vs +15% (INR SD -0.24 +/- 0.14 vs -0.11 +/- 0.18 (P<.001); time in range +28% +/- 20% vs +15% +/- 20% (P<.01)) Methods, limits and funding Outcomes: Stability of anticoagulation (INR) compared with the 6 months before Limitations: Small trial in a narrow group under clinic monitoring. It is not a reason to start vitamin K while on warfarin. Funding and conflicts: No conflict of interest listed; funding not stated in the abstract. Read: abstract
Su 2019 The efficacy and safety of menatetrenone in the management of osteoporosis: a systematic review and meta-analysis of randomized controlled trials. Osteoporos Int · PMID 30734066 · DOI	Systematic review meta analysis	8882 18 randomised trials, 8,882 people with osteoporosis	Menatetrenone (vitamin K2 as MK-4) used as an osteoporosis medicine Oral Not given in the abstract Not given in the abstract · vs Placebo or other osteoporosis drugs	Menatetrenone improved lumbar bone density and lowered the ucOC/OC ratio compared with placebo. The fall in vertebral fractures was not statistically significant. Adverse events and adverse drug reactions were more common than with placebo, but serious adverse events were not. Lumbar BMD MD 0.05 g/cm2; ucOC/OC -21.78%; vertebral fracture RR 0.87; adverse events RR 1.47 (Lumbar BMD 0.01 to 0.09; ucOC/OC -33.68 to -9.87%; fracture RR 0.87 (0.64 to 1.20); adverse events RR 1.47 (1.07 to 2.02); adverse drug reactions RR 1.29 (1.07 to 1.56)) Methods, limits and funding Outcomes: Lumbar BMD; ucOC/OC ratio; vertebral fractures; adverse events Limitations: This is MK-4 as a medicine, so it does not apply to other vitamin K forms. Some results rest on only 2 to 5 trials. The record lists an erratum that was not read. Funding and conflicts: No conflict of interest listed; funding not stated in the abstract. Read: abstract
Violi 2016 Interaction Between Dietary Vitamin K Intake and Anticoagulation by Vitamin K Antagonists: Is It Really True?: A Systematic Review. Medicine (Baltimore) · PMID 26962786 · DOI	Systematic review	2 dietary-intervention trials and 9 observational studies of people on vitamin K antagonists (mostly warfarin)	Dietary vitamin K1 (food) in people on warfarin-type drugs Food Median intake across studies 76 to 217 micrograms a day (as reported) Differs by study	Studies disagreed. Some found higher vitamin K intake lowered INR, others suggested a minimum amount is needed for good control. An effect on clotting was seen mainly with high intakes (above 150 micrograms a day). The authors say the evidence does not support telling people to cut leafy greens, and that stable eating habits matter more. Effect noted mainly above 150 micrograms a day intake (Not applicable) Methods, limits and funding Outcomes: INR changes and anticoagulation control Limitations: Mixed, mostly observational studies with different targets and measures. Funding and conflicts: No conflict of interest listed. Read: abstract
Vossen 2026 Two Years of Menaquinone-7 Supplementation and Coronary Artery Calcification: A Randomized Clinical Trial. JAMA Cardiol · PMID 42268593 · DOI	Randomised controlled trial	180 180 people with symptoms of coronary artery disease and a calcium score of 50 to 400; 85 analysed on MK-7 and 82 on placebo (Netherlands)	Menaquinone-7 (MK-7) Capsules 360 micrograms a day (trial amount, not advice) 2 years · vs Identical placebo	CAC scores rose less on MK-7 than on placebo (placebo 145 to 214 AU; MK-7 135 to 184 AU, P=.02). Blood MK-7 rose as expected. No significant adverse effects were seen. The authors say the clinical meaning for plaque stability is not known; heart attacks and deaths were not the outcome. CAC score at 2 years: placebo median 214 AU; MK-7 median 184 AU; between-group P=.02 (Medians: placebo 145 to 173 to 214; MK-7 135 to 150 to 184 (IQR given in the abstract); P=.02) Methods, limits and funding Outcomes: Coronary artery calcium (CAC) score and calcium mass on CT scan; new calcifications; adverse effects Limitations: One trial of one form (MK-7) in a specific group. A scan marker is not the same as fewer heart attacks. Funding and conflicts: Funding is not stated in the abstract; manufacturer links were not checked. Registration: NCT01002157 Read: abstract
Zhao 2024 The effect of vitamin K supplementation on cardiovascular risk factors: a systematic review and meta-analysis. J Nutr Sci · PMID 38282652 · DOI	Systematic review meta analysis	17 randomised trials of vitamin K supplements and heart-disease risk markers	Vitamin K1 and K2 supplements Oral Differs by trial Differs by trial · vs Placebo	Vitamin K lowered HOMA-IR (an insulin resistance score) slightly. It had no effect on body measures, CRP, glucose or blood fats. The HOMA-IR benefit was larger with K2 than K1. HOMA-IR WMD -0.24; no effect on the other outcomes (HOMA-IR -0.24 (-0.49 to -0.02), P=0.047) Methods, limits and funding Outcomes: Body measures, CRP, blood sugar markers, blood fats, HOMA-IR Limitations: Barely significant on one marker out of many; pooled forms and groups. Funding and conflicts: Authors declare no conflict of interest. Read: abstract
Zhou 2022 Efficacy and safety of vitamin K2 for postmenopausal women with osteoporosis at a long-term follow-up: meta-analysis and systematic review. J Bone Miner Metab · PMID 35711002 · DOI	Systematic review meta analysis	6853 9 randomised trials, 6,853 post-menopausal women with osteoporosis	Vitamin K2 (forms pooled) Oral supplement Amounts differ between trials Long-term follow-up trials · vs Control groups	Vitamin K2 was linked to higher lumbar and forearm bone density and to marker changes. Adverse reactions seemed more common with vitamin K2 (RR 1.33), with no serious adverse events linked to it. Lumbar BMD change WMD 2.17; forearm WMD 1.57; adverse reactions RR 1.33 (Lumbar WMD 2.17 (1.59 to 2.76); forearm WMD 1.57 (1.15 to 1.99); adverse reactions RR 1.33 (1.11 to 1.59)) Methods, limits and funding Outcomes: Lumbar and forearm BMD; osteocalcin markers; adverse reactions Limitations: Read from the abstract only. Fracture results were not given in the abstract. Funding and conflicts: Supported by a provincial research programme in China (Shandong); no conflict of interest listed. Read: abstract
s-efsa-ul-overview EFSA: Overview on Tolerable Upper Intake Levels (SCF and EFSA NDA Panel), version 11, August 2025 · Source	Regulator statement n/a			Methods, limits and funding Read: full-text
s-fda-daily-value FDA: The Daily Value on the Nutrition and Supplement Facts Labels (content current as of 2024-03-05) · Source	Regulator statement n/a			Methods, limits and funding Read: full-text
s-medlineplus-vitamin-k MedlinePlus Medical Encyclopedia: Vitamin K (review date 2025-01-21) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-vitamin-k NHS: Vitamins and minerals, Vitamin K (page last reviewed 2020-08-03) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-warfarin NHS: Warfarin (page last reviewed 2026-02-24) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-ods-vitamin-k NIH Office of Dietary Supplements: Vitamin K fact sheet · Source	Expert review fact sheet n/a			Methods, limits and funding Read: not-read
s-usda-sr-legacy-vitamin-k USDA FoodData Central, SR Legacy (April 2018 release): vitamin K (phylloquinone) values · Source	Nutrient database n/a			Methods, limits and funding Read: full-text

What we do not know yet

No trial was read showing that vitamin K pills help healthy, well-fed adults.
Oral vitamin K for late-onset newborn bleeding was never tested in randomised trials.
Fracture results depend on which trials are counted; no large recent fracture-focused trial of one K2 form was read.
The NIH Office of Dietary Supplements fact sheet could not be read, so interaction lists it may hold are not claimed.
Heart and blood-sugar results are for markers, not for heart attacks or long-term outcomes.
Vitamin K in pregnancy and breastfeeding beyond the official intake figures, contamination of products, and menadione (K3) safety were not researched.

How new research is added

New studies are found by a saved PubMed search and placed in a review queue before the page changes.

Lab markers

What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".

Other 7

●

Time in the target INR range (warfarin)

Higher time in range in one small trial in trials

INR is a blood test of how fast blood clots. People on warfarin aim to stay in a target range; time in range is the share of time they do.

Low certainty

Results and what it means

Why it was measured

To see whether a steady vitamin K supplement steadies warfarin control.

Statistical vs. clinical meaning

A blood-test measure of steadiness, not proof of fewer clots or bleeds.

Safety implication

INR must be checked by the warfarin clinic whenever vitamin K intake changes.

Study	Result	People	Product
¹⁴	Time in range rose 28% (SD 20%) with vitamin K versus 15% (SD 20%) with placebo; INR variability fell -0.24 vs -0.11	70 people on warfarin with unstable control, 6 months	Oral vitamin K1 under clinical supervision

¹⁴

●

Lumbar spine bone mineral density

Slightly higher in several pooled trials; no gain in one add-on trial in trials

A scan (DXA) measure of how dense the bones of the lower spine are.

Mixed findings

Results and what it means

Why it was measured

To see whether vitamin K slows bone loss.

Statistical vs. clinical meaning

A scan measure, not a count of fractures; effects are small and not consistent across trials.

Safety implication

Do not stop prescribed bone treatment.

Study	Result	People	Product
¹⁰	Percent change from baseline: 1 year MD 0.93 (-0.02 to 1.89); 2 years MD 1.63% (0.10 to 3.16); smaller and not significant after removing high-risk-of-bias trials	Post-menopausal or osteoporotic adults, many trials	Oral vitamin K, forms pooled
¹⁹	Lumbar BMD percent change WMD 2.17 (1.59 to 2.76); forearm WMD 1.57 (1.15 to 1.99)	9 trials, 6,853 women with osteoporosis	Vitamin K2
⁹	No significant difference in BMD at total hip, femoral neck or lumbar spine versus placebo	105 women with osteoporosis on a bone drug, 18 months	Vitamin K1 or MK-4

^{10 19 9}

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Undercarboxylated osteocalcin (ucOC) and the ucOC/OC ratio

Lower with vitamin K2 in trials

A blood marker of how well vitamin K is working in bone. A lower ratio means more of the bone protein has been activated by vitamin K.

Moderate certainty

Results and what it means

Why it was measured

It is the most direct blood marker of vitamin K status in bone and is used to confirm that a supplement acted.

Statistical vs. clinical meaning

Confirms vitamin K is acting on bone protein; it does not show stronger bones or fewer fractures.

Safety implication

None specific.

Study	Result	People	Product
⁶	Vitamin K2 reduced serum uc-OC and the uc-OC to cOC ratio in both K2-alone and combined-treatment groups	16 trials, 6,425 post-menopausal women	Vitamin K2
¹⁵	ucOC/OC MD -21.78% (-33.68 to -9.87)	2 trials, 75 people	Menatetrenone (MK-4)

^{6 15}

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Coronary artery calcium (CAC) score

Rose less on MK-7 in one trial in trials

A CT scan score of how much calcium has built up in the heart's arteries, in Agatston units (AU).

Low certainty

Results and what it means

Why it was measured

To see whether MK-7 slows calcium build-up.

Statistical vs. clinical meaning

A scan marker; the authors say clinical significance is not yet known.

Safety implication

No significant adverse effects in the trial.

Study	Result	People	Product
¹⁷	Median score at 2 years 184 AU on MK-7 versus 214 AU on placebo (P=.02)	180 people with symptomatic coronary artery disease	MK-7, 2 years

¹⁷

●

dp-ucMGP (inactive matrix Gla protein)

Lower with vitamin K in trials

A blood marker of vitamin K status in blood vessels. A lower level means more of the protein has been activated by vitamin K.

Moderate certainty

Results and what it means

Why it was measured

Used in dialysis trials as a calcification-risk marker that vitamin K should lower.

Statistical vs. clinical meaning

Shows the vitamin is acting; calcification scores did not change significantly.

Safety implication

None specific.

Study	Result	People	Product
²	K1 SMD -1.64 (-2.05 to -1.23); K2 SMD -0.56 (-0.82 to -0.31)	People on dialysis, 11 trials	Vitamin K1 or K2

●

HOMA-IR (insulin-resistance score)

Slightly lower in trials

A score worked out from fasting glucose and insulin; higher means the body responds less well to insulin.

Low certainty

Results and what it means

Why it was measured

To see whether vitamin K helps the body use insulin.

Statistical vs. clinical meaning

A small lab-marker change at the edge of significance.

Safety implication

Check with a doctor if you take diabetes medicines.

Study	Result	People	Product
¹⁸	WMD -0.24 (-0.49 to -0.02), P=0.047	17 randomised trials	Vitamin K1 and K2
¹	MD -0.63 (-1.20 to -0.06)	8 trials in prediabetes or type 2 diabetes	Vitamin K1 and K2

^{18 1}

●

Fasting glucose and HbA1c

Lower in prediabetes and type 2 diabetes trials in trials

Fasting glucose is blood sugar after not eating; HbA1c reflects average blood sugar over about 3 months.

Low certainty

Results and what it means

Why it was measured

To see whether vitamin K changes blood sugar control.

Statistical vs. clinical meaning

Lab-marker changes from a few moderate-quality trials.

Safety implication

People on diabetes medicines should not add supplements without asking their doctor.

Study	Result	People	Product
¹	Fasting glucose SMD -0.22 (-0.39 to -0.05); HbA1c MD -1.00% (-1.92 to -0.07)	8 trials, prediabetes or type 2 diabetes	Vitamin K1 and K2

Safety

What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.

Main points to know 4

Vitamin K works against the blood thinner warfarin. If you take warfarin, vitamin K changes how it works. The NHS (page reviewed 24 February 2026) 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. MedlinePlus says what matters most is keeping vitamin K intake the same from day to day, because sudden changes alter the drug's effect. A 2016 systematic review found mixed evidence and said stable eating habits matter more than cutting greens. Do not stop or change a prescribed medicine on your own. Authoritative guidance and systematic review ^{24 22 16}
Newborns need vitamin K from their care team, not a home supplement. Babies are born with low vitamin K and can bleed in the first weeks of life, sometimes in the brain. A European position paper says all newborns should receive vitamin K, and that the injection is the preferred route. A 2020 review describes reports of serious bleeding in babies whose parents refused the injection, and found that oral schedules were all less effective than the injection. Ask your midwife or paediatrician about the plan where you live. Guideline and narrative review ^{8 5 11}
No upper limit has been set, which is not the same as proven safe at any amount. EFSA's August 2025 overview of upper intake levels says there are no adequate data to set one for vitamin K. The NHS says there is not enough evidence to know what happens with high supplement amounts, and that supplement amounts of 1 mg (1,000 mcg) or less a day are unlikely to cause harm. These are regulator statements, not advice to take any amount. Regulator statement ^{20 23}
Rare severe allergic reactions have followed vitamin K injected into a vein. A hospital review of 6,572 intravenous doses of vitamin K1 found 2 cases of anaphylaxis (about 3 per 10,000 doses; range 0.04 to 11 per 10,000). The reaction is thought to come from the solvent in the injection, not the vitamin. This is about a hospital injection, not oral supplements or food. Retrospective review ¹²

Side effects 3

Effect	How often	Severity and recovery	Evidence
Mild adverse reactions in trials of vitamin K2 for bone health The abstracts do not say what the reactions were, so no specific side effect is claimed.	Adverse reactions were no different from control in one meta-analysis of 16 trials (RR 1.03, 0.87 to 1.21) but more common in two others: RR 1.33 (1.11 to 1.59) and, for menatetrenone, adverse events RR 1.47 (1.07 to 2.02). Serious adverse events were not significantly different.	Not described in the abstracts; serious events were not significantly more common Not stated in the abstracts.	Meta-analysis ^{6 19 15}
No significant adverse effects in trials of MK-7 and in dialysis trials Both were read from abstracts only and include careful supervision.	The 2-year MK-7 trial reported no significant adverse effects; a pooled analysis in dialysis patients called vitamin K a safe product.	None reported as significant Not applicable	Randomised trial and meta analysis ^{17 2}
Anaphylaxis after intravenous vitamin K1 (medical injection) Thought to be due to the injection's solvent (polyethoxylated castor oil).	About 3 per 10,000 doses (range 0.04 to 11) at one hospital.	Serious but rare Not stated in the abstract.	Retrospective review ¹²

Liver

No liver injury from vitamin K was found in the sources read. A liver-safety reference (LiverTox) was not opened for this page. The liver uses vitamin K to make clotting factors, and bile or gut problems that block absorption can cause deficiency. ²²

How often. No frequency was found.

Monitoring. No agency monitoring advice was found.

This is a safety connection. It is not evidence that Vitamin K supports liver health.

Medicines and supplements 3

With	Why it matters	Importance	Evidence	What to do
Warfarin (a vitamin K antagonist blood thinner) prescription	Warfarin works by opposing vitamin K, so more or less vitamin K changes its effect (MedlinePlus, NHS).	The NHS says not to take vitamin K supplements with warfarin and to talk to the warfarin clinic about high vitamin K foods. MedlinePlus stresses steady day-to-day intake. A 2016 review says restricting greens is not supported and stable habits matter. A small supervised trial found steadier control with a small daily vitamin K1 supplement in people with unexplained unstable control.	Authoritative guidance and systematic review Moderate certainty ^{24 22 16 14}	Do not start, stop or change vitamin K or your greens without your warfarin clinic.
Direct oral anticoagulants (apixaban, rivaroxaban, dabigatran, edoxaban) prescription	A 2022 review says DOACs are affected mainly by drugs acting on P-gp and, less, CYP3A4. Vitamin K is not named in the abstract.	No vitamin K interaction with DOACs was found in the sources read. That is a gap in what was read, not proof that none exists.	Review Not enough evidence ⁷	If you take any blood thinner, ask your prescriber or pharmacist before adding a vitamin K supplement.
Long courses of antibiotics prescription	MedlinePlus says vitamin K deficiency can occur after long-term antibiotic treatment (gut bacteria make some vitamin K).	People with deficiency are often more likely to bruise and bleed. The page does not say how common this is.	Authoritative guidance Low certainty ²²	Ask your prescriber about any bruising or bleeding during long antibiotic treatment.

Who should check first 5

Situation	Advice	Evidence
People taking warfarin	The NHS says not to take vitamin K supplements while on warfarin. Foods can be eaten but affect the drug; talk to the warfarin clinic.	Authoritative guidance ^{24 22}
Pregnancy and breastfeeding	MedlinePlus gives the same US Adequate Intake as for other women of the same age (75 mcg a day for ages 14 to 18; 90 mcg for ages 19 and over, including pregnancy and breastfeeding). These are intake targets, not advice to take pills. No source read covered high-amount supplements in pregnancy or breastfeeding. Ask a doctor, midwife or pharmacist before any supplement.	Authoritative guidance ²²
Newborns, infants and children	Newborns are given vitamin K by their care team to prevent bleeding. MedlinePlus lists Adequate Intakes by age (infants 2.0 and 2.5 mcg; ages 1 to 3, 30 mcg; 4 to 8, 55 mcg; 9 to 13, 60 mcg). These are intake references, not advice. Do not give a child a vitamin K supplement unless a doctor or pharmacist advises it.	Authoritative guidance and guideline ^{22 8}
Kidney disease or dialysis	Trials in people on dialysis were run under medical care and did not show a clear benefit on calcification or survival, though the pooled analysis called vitamin K safe. People with kidney disease should not add vitamin K without their kidney team.	Meta-analysis ²
Allergy to vitamin K injections	Severe allergic reactions have been reported after vitamin K1 injected into a vein. Tell staff about any past reaction to a vitamin K injection.	Retrospective review ¹²

Overdose, product quality and regulators

Summary. No toxic amount of vitamin K1 or K2 from food or supplements has been established in the sources read. EFSA found no adequate data to set an upper level, and the NHS says it is not known what happens with high supplement amounts each day.

Animal. Not reviewed.

High dose or long term signals. No signal from food. Some meta-analyses report slightly more mild adverse reactions with K2 supplements in trials. Menadione (K3) was named by MedlinePlus as a further form; its safety was not researched for this page.

Overdose response. No overdose pattern was found in the sources read. If someone has swallowed a large amount of any supplement, call poison control or emergency services.

Genotoxicity. Not researched.

Contamination and label accuracy of vitamin K products were not researched for this page.

Which form is on the label. K1, MK-4 and MK-7 behave differently in the body: in one small study MK-7 was absorbed and stayed in the blood for up to 48 hours, while MK-4 at nutritional doses was not detectable in blood. Results for one form should not be carried to another. ¹³

Body	Action	Date
MedlinePlus (US National Library of Medicine) (United States)	Lists Adequate Intakes (not an RDA, because evidence is not enough to set one): infants 0 to 6 months 2.0 mcg a day, 7 to 12 months 2.5 mcg; 1 to 3 years 30 mcg; 4 to 8 years 55 mcg; 9 to 13 years 60 mcg; ages 14 to 18 75 mcg (including pregnancy and breastfeeding); males 19 and over 120 mcg; females 19 and over 90 mcg (including pregnancy and breastfeeding). Says people on warfarin should keep vitamin K intake constant day to day. source	2025-01-21
NHS / UK Department of Health and Social Care (United Kingdom)	Says adults need approximately 1 mcg a day for each kilogram of body weight and should get it from a varied diet. Says taking 1 mg (1,000 mcg) or less of vitamin K supplements a day is unlikely to cause harm, and that not enough evidence exists to know the effects of high doses. source	2020-08-03
NHS (warfarin medicine page) (United Kingdom)	Says not to take vitamin K supplements or St John's wort while taking warfarin, and that foods high in vitamin K can affect warfarin, so talk to the warfarin clinic. source	2026-02-24
EFSA and the Scientific Committee on Food (European Union)	Overview of Tolerable Upper Intake Levels (version 11): for vitamin K, no adequate data to derive an upper level. source	2025-08
US Food and Drug Administration (United States)	The Daily Value used on Nutrition and Supplement Facts labels for vitamin K is 120 mcg. source	2024-03-05

When to get medical help

If you take warfarin and have unusual or heavy bleeding, black or bloody stools, a bad headache after a fall, or large bruises you cannot explain: get medical help straight away.
A newborn or baby with unexplained bruises, blood in the urine, stool or vomit, or bleeding that will not stop: call your doctor or emergency services at once.
Hives, swelling of the face or throat, or trouble breathing after any injection: this is an emergency, call emergency services.
Someone has swallowed a large amount of a supplement: call poison control or emergency services.

Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.

General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.

Frequently asked questions

What is vitamin K?

Vitamin K is a fat-soluble vitamin the liver needs to make clotting proteins. Without it blood would not clot. It also has roles in wound healing and, per the NHS, possibly in bones.

^{22 23}

What is the difference between K1 and K2?

K1 (phylloquinone) is the main form in leafy vegetables. K2 (menaquinones, such as MK-4 and MK-7) is made by gut bacteria and found in some foods. In one small study MK-7 raised blood levels and MK-4 did not.

^{22 13}

Is vitamin K2 better than K1?

No head-to-head trial on health outcomes was read. The forms behave differently in the body, and trials of each answer different questions, so results should not be swapped between them.

^{13 2}

Which foods have the most vitamin K?

Leafy greens such as kale, spinach, collards, turnip greens and mustard greens; also broccoli, Brussels sprouts and cabbage. By USDA data a cup of cooked spinach has about 889 mcg of K1 and eggs have under 1 mcg.

^{26 22}

Can I eat salad if I take warfarin?

The NHS says you can still eat foods high in vitamin K but should talk to your warfarin clinic. MedlinePlus says to keep intake steady from day to day. A 2016 review found no good evidence for cutting greens.

^{24 22 16}

Why do newborn babies get vitamin K?

Babies are born with low vitamin K and can bleed in the first weeks of life. A Cochrane review found one injection after birth reduced bleeding in the first week, and a European position paper says all newborns should get it. Ask your midwife or paediatrician about the plan.

^{11 8 5}

Does vitamin K help bones?

Mixed. A 2019 review of 36 trials found no clear effect on density at most sites or on vertebral fractures and called the evidence insufficient. Some K2 trials found small density gains at the lumbar spine.

^{10 6 19 9}

Does vitamin K protect the heart or arteries?

Not shown yet. One 2-year MK-7 trial slowed coronary calcium score progression, but the authors say the clinical meaning is unknown. A pooled analysis found no clear effect on blood fats or CRP, and trials in dialysis patients did not clearly change calcification scores.

^{17 18 2}

Does vitamin K help blood sugar?

Small marker changes were seen in a few moderate-quality trials in prediabetes and type 2 diabetes (fasting glucose, HbA1c, HOMA-IR). That is not proof of better diabetes control, and people on diabetes medicines should ask a doctor first.

^{1 18}

Is there an upper limit for vitamin K?

EFSA's 2025 overview says there are no adequate data to set one. The NHS says 1 mg or less of supplements a day is unlikely to cause harm and that effects of higher amounts are not known. No upper limit is not proof of safety at any amount.

^{20 23}

Who can be short of vitamin K?

MedlinePlus says deficiency is very rare in adults and happens when the gut cannot absorb vitamin K or after long-term antibiotics. Newborns have low levels at birth. Unexplained bruising or bleeding needs a clinician.

^{22 8}

Does vitamin K affect newer blood thinners?

No vitamin K interaction with apixaban, rivaroxaban, dabigatran or edoxaban was found in the sources read, but that is a gap in what was read, not proof. Ask your prescriber or pharmacist.

⁷

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Editorial transparency

Written by: AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
Medical review: None. This page has not been reviewed by a physician or pharmacist.
First published: 2026-10-26
Last substantive update: 2026-10-26
How we research: We started from our existing vitamin K summary, read the MedlinePlus, NHS, FDA and EFSA pages, re-checked food values in saved US Department of Agriculture data, and re-read PubMed abstracts for reviews, trials and guidance. Only abstracts were read for studies. The NIH Office of Dietary Supplements page was blocked and is marked unread.
How we rate evidence: See "How we rate evidence" in the Evidence tab.
Independence: No product is promoted on this page. No affiliate links are shown. Trials of vitamin K products may have manufacturer links not stated in abstracts.

Sources 26

Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.

Ahmed SR, Mokgalaboni K, Phoswa WN. The Differential Effects of Vitamin K Across Glycaemic Outcomes in Prediabetes and Type 2 Diabetes Mellitus.. Nutrients. 2026. PMID 41599883. DOI 10.3390/nu18020269. (abstract)
Andrian T, Stefan A, Nistor I, Covic A. Vitamin K supplementation impact in dialysis patients: a systematic review and meta-analysis of randomized trials.. Clin Kidney J. 2023. PMID 38046003. DOI 10.1093/ckj/sfad255. (abstract)
Hao G, Zhang B, Gu M, et al.. Vitamin K intake and the risk of fractures: A meta-analysis.. Medicine (Baltimore). 2017. PMID 28445289. DOI 10.1097/MD.0000000000006725. (abstract)
Knapen MH, Drummen NE, Smit E, Vermeer C, Theuwissen E. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women.. Osteoporos Int. 2013. PMID 23525894. DOI 10.1007/s00198-013-2325-6. (abstract)
Loyal J, Shapiro ED. Refusal of Intramuscular Vitamin K by Parents of Newborns: A Review.. Hosp Pediatr. 2020. PMID 32019806. DOI 10.1542/hpeds.2019-0228. (abstract)
Ma ML, Ma ZJ, He YL, 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. PMID 36033779. DOI 10.3389/fpubh.2022.979649. (abstract)
Mar PL, Gopinathannair R, Gengler BE, et al.. Drug Interactions Affecting Oral Anticoagulant Use.. Circ Arrhythm Electrophysiol. 2022. PMID 35622425. DOI 10.1161/CIRCEP.121.007956. (abstract)
Mihatsch WA, Braegger C, Bronsky J, et al.. Prevention of Vitamin K Deficiency Bleeding in Newborn Infants: A Position Paper by the ESPGHAN Committee on Nutrition.. J Pediatr Gastroenterol Nutr. 2016. PMID 27050049. DOI 10.1097/MPG.0000000000001232. (abstract)
Moore AE, Dulnoan D, Voong K, et al.. The additive effect of vitamin K supplementation and bisphosphonate on fracture risk in post-menopausal osteoporosis: a randomised placebo controlled trial.. Arch Osteoporos. 2023. PMID 37338608. DOI 10.1007/s11657-023-01288-w. (abstract)
Mott A, Bradley T, Wright K, et al.. 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. 2019. PMID 31076817. DOI 10.1007/s00198-019-04949-0. (abstract)
Puckett RM, Offringa M. Prophylactic vitamin K for vitamin K deficiency bleeding in neonates.. Cochrane Database Syst Rev. 2000. PMID 11034761. DOI 10.1002/14651858.CD002776. (abstract)
Riegert-Johnson DL, Volcheck GW. The incidence of anaphylaxis following intravenous phytonadione (vitamin K1): a 5-year retrospective review.. Ann Allergy Asthma Immunol. 2002. PMID 12392385. DOI 10.1016/S1081-1206(10)62042-X. (abstract)
Sato T, Schurgers LJ, Uenishi K. Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women.. Nutr J. 2012. PMID 23140417. DOI 10.1186/1475-2891-11-93. (abstract)
Sconce E, Avery P, Wynne H, Kamali F. Vitamin K supplementation can improve stability of anticoagulation for patients with unexplained variability in response to warfarin.. Blood. 2007. PMID 17110451. DOI 10.1182/blood-2006-09-049262. (abstract)
Su S, He N, Men P, et al.. The efficacy and safety of menatetrenone in the management of osteoporosis: a systematic review and meta-analysis of randomized controlled trials.. Osteoporos Int. 2019. PMID 30734066. DOI 10.1007/s00198-019-04853-7. (abstract)
Violi F, Lip GY, Pignatelli P, Pastori D. Interaction Between Dietary Vitamin K Intake and Anticoagulation by Vitamin K Antagonists: Is It Really True?: A Systematic Review.. Medicine (Baltimore). 2016. PMID 26962786. DOI 10.1097/MD.0000000000002895. (abstract)
Vossen LM, de Leeuw PW, Schurgers LJ, et al.. Two Years of Menaquinone-7 Supplementation and Coronary Artery Calcification: A Randomized Clinical Trial.. JAMA Cardiol. 2026. PMID 42268593. DOI 10.1001/jamacardio.2026.1279. (abstract)
Zhao QY, Li Q, Hasan Rashedi M, et al.. The effect of vitamin K supplementation on cardiovascular risk factors: a systematic review and meta-analysis.. J Nutr Sci. 2024. PMID 38282652. DOI 10.1017/jns.2023.106. (abstract)
Zhou M, Han S, Zhang W, Wu D. Efficacy and safety of vitamin K2 for postmenopausal women with osteoporosis at a long-term follow-up: meta-analysis and systematic review.. J Bone Miner Metab. 2022. PMID 35711002. DOI 10.1007/s00774-022-01342-6. (abstract)
. EFSA: Overview on Tolerable Upper Intake Levels (SCF and EFSA NDA Panel), version 11, August 2025. . . (full-text)
. FDA: The Daily Value on the Nutrition and Supplement Facts Labels (content current as of 2024-03-05). . . (full-text)
. MedlinePlus Medical Encyclopedia: Vitamin K (review date 2025-01-21). . . (full-text)
. NHS: Vitamins and minerals, Vitamin K (page last reviewed 2020-08-03). . . (full-text)
. NHS: Warfarin (page last reviewed 2026-02-24). . . (full-text)
. NIH Office of Dietary Supplements: Vitamin K fact sheet. . . (not-read)
. USDA FoodData Central, SR Legacy (April 2018 release): vitamin K (phylloquinone) values. . . (full-text)

Where to buy

Check the label first. Whatever you buy, look for these:

Both D3 and K2 are listed with the amount of each per serving
Which form of K2 is used (MK-7 or MK-4)
A third-party testing mark (USP, NSF or ConsumerLab) if you want extra assurance

Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.

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Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.