Home Ingredients Vitamin K
Bone HealthCardiovascular

Vitamin K

Evidence Level
Strong
7 Clinical Trials
5 Documented Benefits
4/5 Evidence Score

Vitamin K is a fat-soluble vitamin essential for blood clotting and for directing calcium into bones rather than soft tissues. It exists mainly as K1, from leafy greens, involved chiefly in clotting, and K2, from fermented foods and animal products, which is more active in supporting bone and cardiovascular health. K2 supplements, often the long-acting MK-7 form, are popular for bone and heart support and are frequently paired with vitamin D and calcium. Vitamin K is generally very safe, but anyone taking the blood thinner warfarin should not change their vitamin K intake without medical guidance, since it directly opposes that drug.

Studied Dose 90–120 mcg/day K1 (RDA); MK-7 (K2): 90–200 mcg/day for bone/cardiovascular; MenaQ7® studies use 180–360 mcg/day MK-7
Active Compound MK-7 (Menaquinone-7) / K1 (Phylloquinone)
Deficiency information View details

Vitamin K deficiency is uncommon in healthy adults because gut bacteria produce some K2 and small amounts are stored in tissues. The main concern is vitamin K deficiency bleeding (VKDB) IN newborns — a potentially fatal condition. All US newborns receive a vitamin K injection at birth to prevent it. In adults, deficiency primarily affects people on long-term antibiotics, those with severe fat malabsorption, or warfarin users.

Common symptoms

  • Easy bruising and prolonged bleeding from minor cuts
  • Bleeding gums, frequent nosebleeds
  • Heavy menstrual bleeding
  • Blood in urine or stool (dark, tarry stools)
  • Internal bleeding — especially gastrointestinal
  • In newborns with VKDB: bleeding from the umbilical stump, mucous membranes, GI tract, or — most seriously — into the brain (intracranial hemorrhage)
  • Signs of internal bleeding in infants: extreme sleepiness, pale skin, bulging fontanelle, vomiting, seizures (MEDICAL EMERGENCY)
  • Increased risk of bone fractures (chronic deficiency affects bone metabolism via osteocalcin)

At-risk groups

  • Newborns who do not receive prophylactic vitamin K injection at birth
  • Exclusively breastfed infants (breast milk is low in vitamin K)
  • Infants with cholestatic liver disease, biliary atresia, or cystic fibrosis
  • People taking warfarin or other vitamin K antagonists (intentional, requires monitoring)
  • People on long-term broad-spectrum antibiotics (alters gut flora)
  • People with severe fat malabsorption (Crohn's, celiac, short-bowel syndrome)
  • People with chronic liver disease
  • People who've had bariatric surgery
When to see a doctor: Any unexplained bleeding in a newborn — bleeding from the umbilical stump, blood in stool, vomiting blood, or signs of brain bleeding (extreme sleepiness, seizures) — is a MEDICAL EMERGENCY requiring immediate ER care. In adults, unexplained easy bruising or bleeding warrants a coagulation panel (PT/INR). Do NOT take vitamin K supplements if you are on warfarin without your doctor's approval — it can dangerously alter your medication's effect.
Explore related deficiencies →
Sources: NIH ODS — Vitamin K Health Professional Fact Sheet · Hemorrhagic Disease of Newborn — StatPearls (NBK558994)

Benefits

Blood Clotting

Vitamin K is essential for synthesizing clotting factors (e.g., prothrombin), ensuring proper coagulation to prevent excessive bleeding from injuries.

Supported by Trial 1, Trial 2

Bone Health

It activates proteins like osteocalcin, which bind calcium to strengthen bones, potentially reducing fracture risk and supporting bone density.

Supported by Trial 2

Heart Health

Vitamin K2 may help prevent arterial calcification by directing calcium to bones instead of blood vessels, though evidence is still emerging.

Supported by Trial 7, Trial 3

Anti-Inflammatory Effects

Some studies suggest vitamin K may reduce inflammation markers, potentially benefiting conditions like arthritis.

Supported by Trial 1, Trial 2

Potential Cognitive Support

Early research indicates vitamin K may play a role in brain health, possibly reducing age-related cognitive decline.

Supported by Trial 6, Trial 4

Mechanism of action

1

Blood Clotting (Coagulation)

Vitamin K is essential for the gamma-carboxylation of glutamate residues in clotting factors II (prothrombin), VII, IX, and X, as well as proteins C, S, and Z, in the liver. This process occurs via the enzyme gamma-glutamyl carboxylase, which uses vitamin K as a cofactor to add carboxyl groups, enabling these proteins to bind calcium ions. Calcium binding allows these factors to interact with phospholipids on cell surfaces, facilitating the clotting cascade to form a stable clot and prevent excessive bleeding.

2

Bone Health

Vitamin K activates osteocalcin, a bone protein produced by osteoblasts, through the same gamma-carboxylation process. Carboxylated osteocalcin binds calcium ions, incorporating them into bone matrix to enhance bone mineralization and strength. It also regulates bone remodeling by influencing osteoblast and osteoclast activity, potentially reducing fracture risk.

3

Vascular Health

Vitamin K2 activates matrix Gla protein (MGP), which inhibits calcium deposition in blood vessels and soft tissues, preventing arterial calcification. This helps maintain vascular elasticity and may reduce cardiovascular risk.

Clinical trials

1
Vitamin K and Cardiovascular Events/Mortality — Evidence Synthesis

2019 pooled analysis of prospective studies on vitamin K (K1, K2) intake and CV events/all-cause mortality. (Eur J)

Pooled across prospective cohorts.

Higher dietary K2 intake associated with reduced CV mortality and events; K1 less consistent. Critical caveat: observational evidence — cannot establish causation. Vitamin K2 supplementation clinical trials needed for definitive conclusions.

2
Vitamin K Intake and Hip Fracture — Evidence Synthesis

2018 pooled analysis of 23 studies (22 observational, 1 clinical trial) with 1,121,582 participants on vitamin K and hip fracture risk.

Pooled across 23 studies.

Higher vitamin K intake associated with modestly reduced hip fracture risk. Mostly observational evidence; OK in pooling but interventional confirmation needed. Note: bone health management primarily uses calcium, vitamin D, K2, weight-bearing exercise, and pharmacotherapy (bisphosphonates, denosumab) for established osteoporosis.

3
Vitamin K for Calcification in Kidney Transplant — Clinical Trial

2021 clinical trial in 40 vitamin K-deficient kidney transplant recipients with high dp-ucMGP levels receiving vitamin K supplementation.

40 KTRs with vitamin K deficiency.

Vitamin K supplementation reduced dp-ucMGP and modestly improved arterial stiffness markers. Note: KTR vitamin K deficiency common; emerging clinical interest.

4
MK-7 for Arterial Stiffness in Postmenopausal Women — Clinical Trial

2015 clinical trial (Knapen et al.) in 244 healthy postmenopausal women receiving 180 µg/day MK-7 (Vitamin K2) for 3 years. (Thromb Haemost)

244 postmenopausal women. 3-year intervention.

MK-7 group showed improved arterial stiffness measures (PWV) vs placebo. Effect emerged after 12 months. Important clinical trial supporting K2 cardiovascular role; MK-7 form preferred for long half-life vs MK-4 (very short half-life requiring multiple daily doses).

5
Vitamin K1 for Hemodialysis Calcification — Trial Protocol

2015 trial protocol (Holden et al.) clinical trial designed to assess vitamin K1 supplementation in hemodialysis patients with vascular calcification.

Hemodialysis patients (protocol).

Trial design only at this citation; subsequent results published. CKD vascular calcification is a major morbidity driver; vitamin K trials in this population emerging.

6
Vitamin K Effects on Vascular Calcification Across Ages — Clinical Trial

Ongoing clinical trial (NCT04676958, registered 2020) in 80 adults (40 young ≤40 years, 40 older) examining vitamin K supplementation effects on vascular calcification.

80 adults across age ranges.

Trial ongoing. Important question — vitamin K's role in age-related vascular calcification.

7
Vitamin K and Vascular Calcification — 2023 Evidence Synthesis

2023 pooled analysis of 14 clinical trials evaluating vitamin K supplementation effects on vascular calcification across populations.

Pooled across 14 clinical trials.

Vitamin K (especially K2/MK-7) modestly reduced vascular calcification progression in some populations. CKD populations showed clearer benefit. Note: large outcomes-focused trials still needed; clinical trial evidence is emerging.

Side effects and drug interactions

Common Potential side effects

Excessive Intake (Rare): Hemolytic anemia (red blood cell breakdown), especially in infants or those with G6PD deficiency. Liver toxicity or jaundice in rare cases, historically linked to high-dose K3 injections. Skin reactions, such as rashes or irritation, with excessive topical or injected forms.
Allergic Reactions: Rare hypersensitivity to vitamin K supplements or injections, potentially causing: Itching, rash, or hives.
Gastrointestinal Issues: High-dose supplements may occasionally cause mild nausea, diarrhea, or stomach upset.
Injection-Specific (Medical Use): Pain or swelling at the injection site. Rare cardiovascular effects (e.g., rapid heartbeat) with rapid IV administration.

Important Drug interactions

Warfarin (Coumadin) — vitamin K directly antagonizes warfarin's anticoagulant mechanism; even small changes in K1 intake can destabilize INR; maintain consistent vitamin K intake and monitor INR closely with K2 supplementation
Antibiotics (broad-spectrum) — may reduce gut bacteria that produce vitamin K2 (menaquinones); may temporarily impair vitamin K status
Orlistat and cholestyramine — reduce absorption of fat-soluble vitamins including vitamin K
Salicylates (aspirin) — high-dose aspirin may impair vitamin K-dependent clotting factor synthesis

Featured in these supplement guides

Bone Density→Inflammation→Menopause Symptoms→Mouth & Gum Health→

More Bone Health Ingredients

Bone Health
Calcium
Calcium is the most abundant mineral in the body — about 99% stored in bones and teeth, wi…
Bone Health
Vitamin D
Vitamin D is a fat-soluble vitamin and steroid hormone precursor essential for calcium abs…
Muscle & Recovery
Magnesium
Magnesium is the fourth most abundant mineral in the body and a cofactor for over 300 enzy…
Bone Health
Copper
Copper is an essential trace mineral and cofactor for over 30 enzymatic reactions, includi…

Explore Other Ingredients

Cognitive
Bacopa Monnieri
Bacopa monnieri (Brahmi) is a cornerstone herb in Ayurvedic medicine with over 3,000 years…
Cognitive
Citicoline
Citicoline (CDP-choline) is a naturally-occurring intermediate in phosphatidylcholine bios…
Cardiovascular
Beetroot
Beetroot is a vegetable rich in dietary nitrate, which the body converts into nitric oxide…

Related articles from our blog

📝 Article
Are Greens Powders Worth It? An Honest Look
Open Instagram and you will be told that one scoop of green powder in water replaces a salad, floods you with energy, an…

Frequently asked questions about Vitamin K

What is the difference between vitamin K1 and K2?

K1 (phylloquinone), from leafy greens, is mainly involved in blood clotting. K2 (menaquinone), from fermented foods and animal products, is more involved in directing calcium into bone and away from arteries. Bone and heart supplements usually feature K2, often the MK-7 form.

How much vitamin K should I take?

The adequate intake is about 90 to 120 mcg per day. K2 supplements commonly provide 90 to 180 mcg of MK-7. Many people pair K2 with vitamin D, since the two work together in calcium metabolism.

Should I take vitamin K with vitamin D?

Many people do, because vitamin D increases calcium absorption while vitamin K2 helps direct that calcium into bone rather than soft tissue. The combination is popular for bone and cardiovascular support, though each can be taken separately.

Who should be cautious with vitamin K?

Anyone taking the blood thinner warfarin, because vitamin K directly opposes how that drug works. If you are on warfarin, do not start or change vitamin K supplements without your doctor's guidance, and keep dietary vitamin K consistent.

What is Vitamin K?

Vitamin K is a fat-soluble vitamin essential for blood clotting and for directing calcium into bones rather than soft tissues. It exists mainly as K1, from leafy greens, involved chiefly in clotting, and K2, from fermented foods and animal products, which is more active in supporting bone and cardiovascular health.

What is Vitamin K used for?

Vitamin K is researched primarily for Bone Health and Cardiovascular. Vitamin K is essential for synthesizing clotting factors (e.g., prothrombin), ensuring proper coagulation to prevent excessive bleeding from injuries.

What are the signs of Vitamin K deficiency?

Vitamin K deficiency is uncommon in healthy adults because gut bacteria produce some K2 and small amounts are stored in tissues. The main concern is vitamin K deficiency bleeding (VKDB) IN newborns — a potentially fatal condition. All US newborns receive a vitamin K injection at birth to prevent it.

What is the recommended dosage of Vitamin K?

The clinically studied dose is 90–120 mcg/day K1 (RDA); MK-7 (K2): 90–200 mcg/day for bone/cardiovascular; MenaQ7® studies use 180–360 mcg/day MK-7 Always follow the product label and check with a healthcare provider for personal advice.

Is Vitamin K safe, and does it have side effects?

For most healthy adults, Vitamin K is well tolerated at studied doses. Reported effects can include: Excessive Intake (Rare): Hemolytic anemia (red blood cell breakdown), especially in infants or those with G6PD deficiency. Liver toxicity or jaundice in rare cases, historically linked to high-dose K3 injections. It may also interact with some medications. Vitamin K is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Vitamin K interact with any medications?

Possible interactions include: Warfarin (Coumadin) — vitamin K directly antagonizes warfarin's anticoagulant mechanism; even small changes in K1 intake can destabilize INR; maintain consistent vitamin K intake and monitor INR closely with K2 supplementation Antibiotics (broad-spectrum) — may reduce gut bacteri… If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Vitamin K?

NutraSmarts rates the evidence for Vitamin K as Strong (4 out of 5). It is backed by 7 clinical trials and 4 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(4 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. 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;95(10):e2895. doi: 10.1097/MD.0000000000002895.PubMedUsed to support: Critical drug-interaction source: systematic review of how vitamin K intake antagonizes warfarin/vitamin K antagonists by affecting INR and anticoagulant efficacy. Establishes that changes in vitamin K (including supplements) can destabilize anticoagulation; the warfarin interaction must be flagged for anyone on these drugs.
  2. 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;24(9):2499-507. doi: 10.1007/s00198-013-2325-6.PubMedUsed to support: 3-year RCT (244 postmenopausal women): MK-7 (menaquinone-7) 180 mcg/d reduced the age-related decline in lumbar spine and femoral neck bone mineral density and bone strength. Supports a modest bone benefit of vitamin K2 via osteocalcin carboxylation.
  3. Geleijnse JM, Vermeer C, Grobbee DE, Schurgers LJ, Knapen MH, van der Meer IM, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100-5. doi: 10.1093/jn/134.11.3100.PubMedUsed to support: Prospective cohort (Rotterdam Study, 4807 subjects): higher dietary menaquinone (K2) intake was associated with lower coronary heart disease mortality, all-cause mortality, and less severe aortic calcification (phylloquinone showed no association). Observational support for the arterial-calcification/cardiovascular hypothesis; association, not proof of causation.
  4. Cockayne S, Adamson J, Lanham-New S, Shearer MJ, Gilbody S, Torgerson DJ. Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Arch Intern Med. 2006;166(12):1256-61. doi: 10.1001/archinte.166.12.1256.PubMedUsed to support: Meta-analysis of 13 RCTs: vitamin K supplementation was associated with reduced bone loss and, in the (largely Japanese, high-dose menaquinone-4) fracture trials, lower vertebral and hip fracture rates. Supports a bone/fracture benefit but honestly notes the fracture data come mainly from Japanese populations and need broader confirmation.