Vitamin K2 (Menaquinone)

Vitamin K2 (menaquinone) is one of the most underappreciated vitamins—and one that your gut bacteria can produce. While vitamin K1 from leafy greens handles blood clotting, vitamin K2 from bacteria and fermented foods directs calcium throughout your body, supporting bone strength while protecting arteries from dangerous calcification.^[1] Vitamin K2 is essential for bone and cardiovascular health as it helps prevent the 'calcium paradox,' which involves a deficiency of calcium in bones and its simultaneous accumulation in vascular walls.^[2]

K2 vs. K1: Not the Same

Vitamin K1 (Phylloquinone)

• Found in leafy green vegetables
• Primary role in blood clotting
• Stays in liver
• Most dietary vitamin K is K1

Vitamin K2 (Menaquinone)

• Produced by bacteria (gut and fermented foods)
• Role in calcium metabolism
• Distributed throughout body
• Several forms: MK-4 through MK-13
• MK-7 and MK-4 most studied

Bacterial Production of K2

Gut Bacteria That Make K2

Several gut bacterial species produce vitamin K2:

• Bacteroides fragilis: Produces MK-10, MK-11
• Escherichia coli: Produces MK-8
• Veillonella species: Various menaquinones
• Enterococcus faecium: MK-4 producer
• Eubacterium lentum: MK-6

How Much Does the Gut Contribute?

This is debated:

• Gut bacteria produce significant K2
• Absorption may be limited (K2 produced in colon, absorption mainly in small intestine)
• Contribution varies by individual and microbiome composition
• Dietary sources still important for optimal levels

The Calcium Paradox and K2

The Problem

Calcium is essential for bones, but when it deposits in arteries, it causes:

• Atherosclerosis (hardened arteries)
• Cardiovascular disease
• Increased heart attack and stroke risk

K2's Solution

Vitamin K2 activates proteins that control calcium:

Osteocalcin (in bone):

• K2 activates osteocalcin
• Active osteocalcin binds calcium to bone matrix
• Increases bone strength

Matrix Gla Protein (MGP) (in arteries):

• K2 activates MGP
• Active MGP prevents calcium deposits in arteries
• Protects against vascular calcification

Result: Calcium goes to bones (good) not arteries (bad) [^vermeer2012]

Health Benefits

Bone Health

K2 supports strong bones:

• Increases bone mineral density: Multiple studies show benefit
• Reduces fracture risk: Significant reduction in hip, vertebral fractures
• Works with D3 and calcium: Synergistic effects
• Japan uses MK-4: Approved for osteoporosis treatment

Cardiovascular Protection

The Rotterdam Study showed dramatic heart benefits.^[3] Vitamin K2 promotes cardiovascular health by activating matrix Gla protein, which inhibits vascular and valvular calcification and reduces arterial stiffness.^[4]

• 57% reduced coronary heart disease with highest K2 intake
• 52% reduced aortic calcification
• 26% reduced all-cause mortality
• K1 showed no cardiovascular benefit

Dental Health

K2 may support oral health:

• Activates proteins in saliva
• May help with proper tooth development
• Possible cavity prevention
• Research ongoing

Other Potential Benefits

Vitamin K2 is a critical nutrient that regulates calcium distribution and energy metabolism across multiple body systems to support bone, cardiovascular, and neurological health.^[5] Vitamin K2 supplementation may serve as a critical adjunct for bone and cardiovascular health by reducing fractures and vascular calcification, while showing potential benefits for other chronic conditions like diabetes and cancer.^[6]

• Brain health: K2 found in brain, may protect neurons
• Cancer: Some studies suggest protective effects
• Kidney health: May reduce kidney stones
• Skin health: Involved in elastin function

Food Sources of K2

Fermented Foods (Best Sources)

Food	K2 Form	Amount (mcg/100g)
Natto (fermented soy)	MK-7	1000+
Gouda/Edam cheese	MK-8, MK-9	75
Brie/soft cheeses	Various	50
Blue cheese	Various	36
Sauerkraut	MK-4 to MK-7	Varies

Animal Products

Food	K2 Form	Amount (mcg/100g)
Goose liver	MK-4	369
Chicken liver	MK-4	14
Egg yolk	MK-4	32
Butter (grass-fed)	MK-4	15
Chicken dark meat	MK-4	27

The Natto Champion

Natto (fermented soybeans) is exceptionally high in K2:

• 1000+ mcg MK-7 per 100g
• Traditional Japanese food
• Acquired taste (strong flavor, sticky texture)
• Best food source by far

MK-4 vs. MK-7

The two most important K2 forms differ:

Property	MK-4	MK-7
Source	Animal products	Fermented foods, bacteria
Half-life	Short (hours)	Long (days)
Dosing	Multiple times daily	Once daily
Tissue distribution	Wide	Wide
Supplement dose	500-1000 mcg	100-200 mcg

Both forms are effective; MK-7's longer half-life makes it more practical for supplementation.

Supporting Bacterial K2 Production

Microbiome Strategies

While gut-produced K2's contribution is debated, supporting producing bacteria can't hurt:

1. Diverse diet: Supports varied microbiome
2. Fermented foods: Both provide K2 and support bacteria
3. Fiber intake: Feeds beneficial bacteria
4. Avoid unnecessary antibiotics: Preserve K2 producers

Absorption Considerations

Even if bacteria produce K2:

• Most is made in colon
• K2 is fat-soluble (needs fat for absorption)
• Small intestine is primary absorption site
• Some colonic absorption possible

Who Needs More K2?

Higher-Risk Groups

• Elderly: Decreased absorption and production
• Those on statins: May interfere with K2 metabolism
• Low dairy consumers: Miss fermented cheese sources
• Antibiotic users: Depleted K2-producing bacteria
• Those with malabsorption: Cystic fibrosis, celiac, IBD
• Warfarin users: Need consistent (not necessarily low) K intake

Testing K2 Status

Available Tests:

• Serum vitamin K: Direct measurement (not widely available)
• Undercarboxylated osteocalcin (ucOC): Functional marker for bone
• Dephospho-uncarboxylated MGP (dp-ucMGP): Marker for vascular status

Interpretation:

• High ucOC = insufficient K2 for bone
• High dp-ucMGP = insufficient K2 for arteries
• Both can indicate K2 deficiency

Supplementation

When to Consider

• Limited dietary K2 intake
• Osteoporosis or osteopenia
• High cardiovascular risk
• Arterial calcification present
• Taking calcium and D3 supplements (add K2!)

Dosing

• MK-7: 100-200 mcg daily
• MK-4: 500-1000 mcg, 2-3 times daily
• Combination products: With D3 and calcium

Safety

• Generally very safe
• No known toxicity at supplemental doses
• Warfarin users: Requires medical supervision (K2 affects warfarin)
• May interact with some medications

The D3-K2 Synergy

Why They Work Together

Vitamin D3 and K2 are complementary:

1. D3 increases calcium absorption from gut
2. K2 directs that calcium to bones (not arteries)
3. Without K2, more calcium may end up in wrong places
4. Always combine if taking D3 supplements

Optimal Ratio

Various recommendations exist:

• General: 100 mcg K2 per 1000 IU D3
• Higher D3 doses may need proportionally more K2
• No official guidelines yet

Practical Recommendations

Dietary Approach

1. Include fermented foods (natto, aged cheese, sauerkraut)
2. Eat egg yolks and grass-fed animal products
3. Don't fear dietary fat (needed for absorption)
4. Consider traditional diets (many include fermented foods)

Supplementation Approach

1. Consider MK-7 supplement (100-200 mcg)
2. Combine with D3 and calcium if taking those
3. Take with fat-containing meal
4. Consult doctor if on warfarin

Support Gut Bacteria

1. Eat diverse, fiber-rich foods
2. Include fermented foods regularly
3. Minimize unnecessary antibiotics
4. Maintain healthy microbiome