What does vitamin K2 do and why is it important?

Vitamin K2 activates two critical proteins that regulate where calcium is deposited in the body. Osteocalcin in bone requires K2-dependent carboxylation to bind calcium and incorporate it into bone mineral; without K2, osteocalcin remains undercarboxylated and calcium is not effectively directed into bone. Matrix Gla protein (MGP) in arterial walls requires K2-dependent carboxylation to actively inhibit vascular calcification; without adequate K2, MGP remains inactive (undercarboxylated), and calcium deposits freely in arterial walls, heart valves, and soft tissues. K2 is therefore the master regulator of calcium trafficking: directing calcium into bone where it belongs and preventing it from depositing in arteries and soft tissues where it causes damage.

What is the optimal vitamin K2 level?

In functional medicine, optimal serum MK-7 is above 1.0 ng/mL. Standard reference ranges vary considerably by assay and laboratory. Western populations typically have very low MK-7 levels (often below 0.5 ng/mL) due to minimal natto consumption and low fermented food intake, in contrast to Japanese populations consuming traditional natto who have MK-7 levels above 2 to 3 ng/mL and significantly lower rates of arterial calcification and osteoporotic fracture.

What foods contain vitamin K2?

The primary dietary K2 sources are: natto (fermented soybeans; by far the highest K2 source at 200 to 1,000 mcg MK-7 per 100g; traditional Japanese food with minimal Western consumption), hard cheeses (particularly Gouda and Brie; 50 to 75 mcg MK-4 per 100g), soft cheeses (25 to 50 mcg MK-4 per 100g), egg yolks (5 to 10 mcg MK-4 per egg), butter from grass-fed cows (higher K2 than grain-fed dairy), and fermented vegetables. Most Western diets provide very little K2, making supplementation the most practical strategy for most patients.

Lab Reference Library / Vitamin K2 (MK-7) Nutritional & Micronutrient

Vitamin K2 (MK-7)

Q: What is the difference between vitamin K1 and vitamin K2?

Vitamin K1 (phylloquinone) is found primarily in leafy green vegetables and is taken up efficiently by the liver for clotting factor synthesis (factors II, VII, IX, X, protein C, and protein S). It has minimal impact on extrahepatic K2-dependent proteins. Vitamin K2 (menaquinone) exists in several forms: MK-4 (found in fermented foods and animal products; short half-life of 1 to 2 hours) and MK-7 (found in natto fermented soybeans; much longer half-life of 48 to 72 hours, allowing once-daily dosing and more stable tissue saturation). K2 distributes to extrahepatic tissues including bone and arterial walls where it activates osteocalcin and MGP. Most Westerners consume adequate K1 but severely insufficient K2.

Q: Why must vitamin K2 be taken with vitamin D3?

Vitamin D3 supplementation increases calcium absorption from the gut and promotes osteocalcin protein production in bone. If K2 is inadequate, the additional calcium absorbed from D3 supplementation and the osteocalcin produced cannot be directed into bone effectively; instead, calcium may accumulate in soft tissues and arteries. K2 is required to activate the proteins that direct this additional calcium appropriately. This is why high-dose vitamin D3 supplementation without adequate K2 may theoretically worsen arterial calcification in K2-deficient individuals, and why functional medicine protocols consistently pair D3 supplementation with K2 (typically 100 to 200 mcg MK-7 per 5,000 IU D3).

K2 · Menaquinone-7 · Vitamin K2 MK-7

Reference range, optimal functional medicine levels, and why vitamin K2 is the most underappreciated cardiovascular nutrient, directing calcium into bone and away from arteries, why deficiency drives arterial calcification independent of calcium intake, and why K2 and vitamin D must be supplemented together.

Most SearchedFat-Soluble Vitamin

Standard Range (MK-7)0.1 to 3.2 ng/mL

FM OptimalAbove 1.0 ng/mL

Fasting RequiredNo

Unitsng/mL

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Category: Nutritional & Micronutrient | Also known as: Menaquinone-7, MK-7, Vitamin K2 MK-7, Serum Menaquinone

1. What This Test Measures

Vitamin K2 (menaquinone) is a fat-soluble vitamin that activates K2-dependent proteins through gamma-carboxylation of glutamate residues. The two most clinically significant K2-dependent proteins are osteocalcin (in bone, required for calcium binding and incorporation into bone mineral matrix) and matrix Gla protein (MGP, in arterial walls and soft tissues, the primary endogenous inhibitor of vascular calcification). Serum MK-7 (menaquinone-7) is the most commonly measured K2 form due to its long half-life of 48 to 72 hours, which allows once-daily supplementation and more stable serum levels than MK-4.

Vitamin K2 should not be confused with vitamin K1 (phylloquinone), which is found in leafy green vegetables and is taken up primarily by the liver for clotting factor synthesis. K1 has minimal effect on extrahepatic K2-dependent proteins like osteocalcin and MGP. Most Westerners consume adequate K1 but severely insufficient K2 because the primary dietary K2 sources (natto, aged cheeses, pastured animal fats) are minimally consumed in modern Western diets.

2. Optimal Range

Serum MK-7	Interpretation
Below 0.3 ng/mL	Very low: MGP significantly undercarboxylated; active vascular calcification risk
0.3 to 1.0 ng/mL	Low: insufficient K2 for optimal MGP and osteocalcin carboxylation
Above 1.0 ng/mL	Optimal: adequate K2 for MGP and osteocalcin activation
Above 2.0 to 3.0 ng/mL	Excellent: traditional Japanese natto-consuming population range; lowest arterial calcification rates

Reference ranges vary significantly by assay platform. Western populations without natto consumption or targeted K2 supplementation typically have MK-7 below 0.5 ng/mL. Direct measurement is available but undercarboxylated osteocalcin (ucOC) and undercarboxylated MGP (dp-ucMGP) are functionally more informative markers of K2 adequacy but are not widely available on standard laboratory panels.

3. The Calcium Trafficking Mechanism

What K2 Does Correctly

Activates osteocalcin in bone: K2-carboxylated osteocalcin binds calcium and hydroxyapatite, incorporating calcium into bone mineral matrix where it provides structural strength
Activates MGP in arteries: K2-carboxylated MGP binds calcium in arterial walls and prevents calcium crystal nucleation and growth, actively blocking vascular calcification
Net result: calcium flows into bone and is prevented from depositing in arteries
K2 does not increase calcium absorption (that is vitamin D's role); it directs already-absorbed calcium to the correct compartment

What K2 Deficiency Causes

Undercarboxylated osteocalcin cannot bind calcium; bone mineral density declines despite adequate calcium intake
Undercarboxylated MGP cannot inhibit vascular calcification; calcium deposits freely in arterial walls, heart valves, and soft tissues
Arterial calcification from K2 deficiency occurs independently of calcium intake; it is not caused by "too much calcium" but by insufficient K2 to direct calcium away from arteries
Calcific aortic valve stenosis and coronary artery calcification are strongly associated with low K2 status in population studies

4. Why K2 Must Be Paired with Vitamin D3

Vitamin D3 increases calcium absorption and promotes osteocalcin production; vitamin K2 activates the proteins that direct this additional calcium appropriately. Without adequate K2, the additional calcium absorbed from D3 supplementation and the osteocalcin produced may not be directed into bone efficiently, and calcium may accumulate in soft tissues and arteries. This is why functional medicine protocols consistently pair D3 with K2: 100 to 200 mcg MK-7 per 5,000 IU D3 supplemented together. Giving D3 alone to a K2-deficient patient is potentially counterproductive for vascular health.

5. Evidence from Population Studies

Rotterdam Study (2004): in 4,807 Dutch adults followed for 10 years, the highest tertile of dietary K2 intake was associated with 57% lower risk of coronary heart disease mortality and 52% lower risk of severe aortic calcification compared to the lowest tertile; vitamin K1 was not associated with cardiovascular outcomes
Prospect-EPIC cohort: highest K2 intake associated with reduced coronary heart disease incidence; again, K1 showed no significant association
ECKO trial: MK-4 supplementation (45mg daily) significantly reduced vertebral fractures and slowed bone mineral density loss in osteoporotic women over 2 years
Japanese population data: Japanese populations consuming traditional natto (highest K2 food source) have significantly lower rates of hip fracture and arterial calcification compared to Japanese populations not consuming natto, despite similar total calcium intake

6. Supplementation Guidance

Dietary Sources

Natto: 200 to 1,000 mcg MK-7 per 100g; by far the highest source; fermented soybeans with minimal Western consumption
Hard cheeses (Gouda, Brie, Edam): 50 to 75 mcg MK-4 per 100g
Soft cheeses: 25 to 50 mcg MK-4 per 100g
Butter from grass-fed cows: higher K2 than grain-fed; approximately 10 to 15 mcg MK-4 per tablespoon
Egg yolks from pastured hens: 5 to 10 mcg MK-4 per egg
Liver and organ meats: modest MK-4 content

Supplemental Forms

MK-7 (menaquinone-7): preferred supplemental form; long half-life (48 to 72 hours) allows once-daily dosing and maintains stable serum levels; derived from natto fermentation; most common in functional medicine protocols
MK-4 (menaquinone-4): short half-life (1 to 2 hours); synthetic form; used at very high doses (45mg daily) in Japanese clinical trials for osteoporosis; lower doses may require multiple daily doses for consistent activity
Standard functional medicine dose: 100 to 200 mcg MK-7 daily paired with each 5,000 IU D3 dose
Take with the largest meal of the day (fat-soluble; absorption requires dietary fat)
Note: K2 does not interfere with anticoagulant medications at standard dietary doses, but patients on warfarin should consult their prescribing physician before changing K2 intake significantly

Clinical Monitoring

Recheck serum MK-7 at 3 months after initiating supplementation to confirm target above 1.0 ng/mL
Coronary artery calcium (CAC) score: the most direct measure of arterial calcification burden; K2 optimization is part of the CAC reduction protocol alongside statin therapy, omega-3s, and Lp-PLA2 reduction
Bone density (DEXA scan): K2 optimization is a component of the comprehensive osteoporosis prevention protocol alongside vitamin D, calcium, magnesium, resistance training, and weight-bearing exercise
Undercarboxylated osteocalcin (ucOC) and dp-ucMGP: functional K2 adequacy markers superior to serum MK-7 but not widely available; ucOC above 30% of total osteocalcin suggests functional K2 insufficiency

7. Related Lab Tests

Vitamin DMust Be Paired with K2 for Safe Calcium Trafficking

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RBC MagnesiumCo-nutrient for Bone Mineral Metabolism

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ApoBArterial Calcification Risk Context

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Lp-PLA2Plaque Inflammation Drives Calcification

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CalciumK2 Directs Calcium into Bone Away from Arteries

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Vitamin AShares RXR Receptor Pathway; Co-regulate Together

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8. Clinical Perspective

Clinical Perspective

Vitamin K2 is the nutrient that made me reconsider how I think about arterial calcification. For years the conversation about calcium in arteries was framed around calcium intake and cholesterol, when the more accurate question is where does absorbed calcium actually go? K2 is the traffic director. Without adequate K2, matrix Gla protein in the arterial wall stays undercarboxylated and inactive, calcium deposits in the vessel wall, and the arterial calcification process that was supposed to be inhibited by MGP proceeds unchecked. I pair K2 with every patient on vitamin D3, without exception, and I test baseline serum MK-7 in patients with elevated coronary artery calcium scores or known arterial disease. This is a nutrient that most patients have never heard of, but it may be one of the most important cardiovascular nutrients available from a calcium trafficking perspective.

Brian Lamkin, DO | Founder, The Lamkin Clinic | Edmond, Oklahoma

9. Frequently Asked Questions

What does vitamin K2 do?

Vitamin K2 activates two critical proteins that regulate calcium distribution: osteocalcin in bone (which must be K2-carboxylated to bind calcium and incorporate it into bone mineral) and matrix Gla protein (MGP) in arterial walls (which must be K2-carboxylated to actively inhibit vascular calcification). K2 directs calcium into bone where it belongs and prevents it from depositing in arteries and soft tissues.

What is the difference between vitamin K1 and vitamin K2?

K1 (phylloquinone) from leafy greens is taken up primarily by the liver for clotting factor synthesis and has minimal effect on extrahepatic K2-dependent proteins. K2 (menaquinone) distributes to bone and arterial tissue where it activates osteocalcin and MGP. Most Westerners consume adequate K1 but severely insufficient K2, making K2 supplementation clinically important.

Why must vitamin K2 be taken with vitamin D3?

Vitamin D3 increases calcium absorption and promotes osteocalcin protein production. Without adequate K2, the additional calcium absorbed and the osteocalcin produced cannot be directed effectively into bone; instead, calcium may deposit in soft tissues and arteries. K2 is the necessary partner that activates the proteins directing D3-enhanced calcium to appropriate compartments.

Does vitamin K2 interfere with blood thinners?

Standard dietary and supplemental doses of vitamin K2 (100 to 200 mcg MK-7 daily) have minimal effect on warfarin anticoagulation because warfarin targets the clotting factor carboxylation pathway (dependent primarily on K1) rather than the extrahepatic proteins activated by K2. However, patients on warfarin should maintain consistent K2 intake and consult their prescribing physician before significantly changing K2 supplementation, as individual responses vary.

Content authored and clinically reviewed by Brian Lamkin, DO, founder of The Lamkin Clinic in Edmond, Oklahoma. Brian Lamkin, DO has 25+ years of experience in functional and regenerative medicine. This page reflects current functional medicine practice standards and is updated as new clinical evidence becomes available.

Calcium deposits in arteries not because you eat too much calcium but because you lack adequate K2 to direct it into bone instead.

K2, D3, and magnesium form the foundational bone-cardiovascular calcium management trio. Schedule a consultation for a complete fat-soluble vitamin and cardiovascular calcification assessment.

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Medical Disclaimer: This content is provided for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Lab interpretation should always be performed in clinical context by a qualified healthcare provider. Reference ranges and optimal targets may vary based on individual patient history, clinical presentation, and laboratory methodology. Schedule a consultation to discuss your specific results with Dr. Lamkin.