What is Vitamin K?
Vitamin K is a fat-soluble vitamin that exists in several forms, with two primary types:
Vitamin K1 (Phylloquinone):
Found in green plants and leafy vegetables
Primary form in most diets
Essential for blood clotting
Shorter half-life in the body (hours)
Concentrated in the liver
Vitamin K2 (Menaquinone):
Produced by bacteria (including gut bacteria)
Found in fermented foods and animal products
Multiple subtypes (MK-4 through MK-13)
Longer half-life (days to weeks)
Distributed throughout body tissues
Key K2 Subtypes:
MK-4 (Menatetrenone): Found in animal products, short half-life (1-2 hours)
MK-7: From fermented foods (natto), long half-life (72+ hours)
MK-8, MK-9: From cheese and other fermented products
MK-13: Longest chain, found in some fermented foods
Primary Functions & Benefits
Essential Functions:
Blood Clotting (Primarily K1):
Activates clotting factors II, VII, IX, and X
Enables proper hemostasis (stopping bleeding)
Essential for surgical procedures and injury recovery
Bone Health (Primarily K2):
Activates osteocalcin (bone-building protein)
Directs calcium into bones and teeth
Prevents bone mineral loss
Supports bone density and fracture prevention
Cardiovascular Health (Primarily K2):
Activates matrix Gla protein (MGP)
Prevents calcium deposits in arteries
Maintains arterial flexibility
Reduces cardiovascular disease risk
Other Functions:
Gene expression: Regulates various proteins
Cell growth: Supports proper cell division
Brain health: May protect against cognitive decline
Cancer prevention: Some protective effects in research
Health Benefits:
Bone Health:
Reduces fracture risk by 60-81% in some studies
Improves bone mineral density
Enhances bone quality, not just quantity
Particularly beneficial for postmenopausal women
Cardiovascular Protection:
Reduces arterial calcification by up to 50%
Improves arterial elasticity
May reduce heart disease risk by 9-57%
Lowers risk of cardiovascular mortality
Dental Health:
Strengthens tooth enamel
Reduces cavities and tooth decay
Supports proper tooth development
May reduce need for dental interventions
Potential Benefits:
Cognitive function: May reduce dementia risk
Cancer prevention: Particularly liver and prostate cancer
Insulin sensitivity: May improve glucose metabolism
Kidney health: Prevents kidney stone formation
Recommended Daily Amounts
Official Adequate Intake (AI) - Total Vitamin K:
Infants 0-6 months: 2.0 mcg
Infants 7-12 months: 2.5 mcg
Children 1-3 years: 30 mcg
Children 4-8 years: 55 mcg
Children 9-13 years: 60 mcg
Males 14-18 years: 75 mcg
Females 14-18 years: 75 mcg
Males 19+ years: 120 mcg
Females 19+ years: 90 mcg
Pregnancy: 90 mcg
Breastfeeding: 90 mcg
Optimal Intake Recommendations (Based on Research):
For Bone Health:
MK-4: 15-45 mg daily (therapeutic doses)
MK-7: 100-200 mcg daily
Total K2: 100-300 mcg daily
For Cardiovascular Health:
MK-7: 180-360 mcg daily
Combined with vitamin D: K2 needs may be higher
Maintenance/Prevention:
K1: 100-500 mcg daily (from food/supplements)
K2: 100-200 mcg daily
Total: 200-500 mcg daily
Note: No established upper limit due to low toxicity risk
Food Sources
Vitamin K1 (Phylloquinone) Sources:
Excellent Sources (>100 mcg per serving):
Kale: 1,062 mcg per cup (cooked)
Spinach: 889 mcg per cup (cooked)
Collard greens: 836 mcg per cup (cooked)
Swiss chard: 573 mcg per cup (cooked)
Parsley: 984 mcg per cup (fresh)
Good Sources (20-100 mcg per serving):
Broccoli: 220 mcg per cup (cooked)
Brussels sprouts: 218 mcg per cup (cooked)
Cabbage: 163 mcg per cup (cooked)
Lettuce: 57 mcg per cup (raw)
Green beans: 20 mcg per cup (cooked)
Other Sources:
Vegetable oils: Soybean, canola, olive oil
Herbs: Basil, sage, oregano
Green tea: Moderate amounts
Vitamin K2 (Menaquinone) Sources:
MK-7 Sources:
Natto (fermented soybeans): 1,062 mcg per 100g - highest source
Fermented vegetables: Sauerkraut, kimchi (variable)
Some cheeses: Particularly aged, hard cheeses
MK-4 Sources:
Grass-fed animal products: Higher than grain-fed
Egg yolks: 32 mcg per 100g (from pasture-raised hens)
Chicken liver: 14 mcg per 100g
Beef liver: 11 mcg per 100g
Ground beef: 8 mcg per 100g
Chicken breast: 8 mcg per 100g
MK-8, MK-9 Sources:
Hard cheeses: Gouda, Edam, aged cheddar
Soft cheeses: Brie, blue cheese
Butter: From grass-fed cows
Factors Affecting Content:
Grass-fed vs. grain-fed: Dramatically affects K2 content
Fermentation: Increases K2 content significantly
Storage and processing: Can reduce vitamin K content
Seasonal variation: Fresh foods vary by harvest time
Supplementation Guidelines
Types of Supplements:
Vitamin K1 (Phylloquinone):
Synthetic: Most common form in supplements
Natural: From alfalfa extract
Typical doses: 100-1,000 mcg
Vitamin K2 (Menaquinone): MK-4 (Menatetrenone):
Synthetic: Most research-backed form
Therapeutic doses: 15-45 mg daily
Short half-life: Requires multiple daily doses
MK-7:
Natural: From natto extract (Bacillus subtilis)
All-trans form: Most bioactive configuration
Long half-life: Once daily dosing
Typical doses: 100-320 mcg daily
Recommended Supplement Strategy:
Best Options:
MK-7 (100-200 mcg): For daily maintenance
Combined K1 + MK-7: Comprehensive approach
MK-4 (15-45 mg): For therapeutic bone treatment
Full spectrum: K1 + multiple K2 forms
Avoid:
K1 only supplements: Miss cardiovascular/bone benefits of K2
Synthetic MK-7: cis-isomers may be less effective
Very low doses: <50 mcg unlikely to provide optimal benefits
Timing & Administration:
Take with fat-containing meals for optimal absorption
MK-7: Once daily (long half-life)
MK-4: 2-3 times daily (short half-life)
With or without food: Both effective, but fat enhances absorption
Consistent timing: Helps maintain steady levels
Synergistic Supplements
Essential Partners:
Vitamin D3: 1,000-4,000 IU daily
Critical partnership: D3 increases calcium absorption, K2 directs it properly
Prevents calcium paradox: Calcium in bones, not arteries
Synergistic bone benefits: Much more effective together
Safety: K2 prevents vitamin D toxicity symptoms
Magnesium: 300-400 mg daily
Bone mineralization: Works with K2 and D3 for bone health
Cardiovascular support: Enhances K2's arterial benefits
Vitamin D activation: Required for vitamin D metabolism
Calcium: 500-1,000 mg daily (preferably from food)
Requires K2: To direct calcium to bones, not soft tissues
Timing: Take together for optimal utilization
Type matters: Calcium citrate or hydroxyapatite preferred
Beneficial Combinations:
Vitamin A: Supports K2 functions and bone health
Boron: Enhances vitamin D and K2 effectiveness
Strontium: Works with K2 for bone building
Omega-3s: Anti-inflammatory support for bone and cardiovascular health
Interactions & What NOT to Take
Critical Drug Interactions:
Anticoagulants (Blood Thinners): Warfarin (Coumadin):
Major interaction: Vitamin K directly counteracts warfarin
Consistency key: Maintain steady K intake, don't avoid entirely
Monitor INR: More frequent testing if changing K intake
Medical supervision: Required for any supplementation
Novel Anticoagulants:
Dabigatran, rivaroxaban, apixaban: Less interaction than warfarin
Still use caution: Consult physician before supplementing
Monitor bleeding: Watch for unusual bleeding or bruising
Medications That May Interact:
Antibiotics:
Broad-spectrum: May reduce gut bacteria that produce K2
Long-term use: May increase vitamin K needs
Timing: Take K supplements away from antibiotics
Cholesterol Medications:
Bile acid sequestrants: May reduce K absorption
Take separately: 4+ hours apart from medication
Weight Loss Drugs:
Orlistat: Blocks fat absorption, reducing K uptake
Increase intake: May need higher doses with these medications
Supplements That May Interfere:
High-Dose Vitamin E (>400 IU):
Antagonistic: May interfere with vitamin K function
Blood clotting: Can enhance anticoagulant effects
Balance needed: Moderate doses of both vitamins
High-Dose Vitamin A (>10,000 IU):
May interfere: With vitamin K metabolism at very high doses
Moderation: Normal doses are synergistic
Who Should Take Vitamin K
High-Priority Groups:
Bone Health Concerns:
Postmenopausal women: Highest fracture risk
People with osteoporosis/osteopenia: Proven benefits
Family history of fractures: Prevention strategy
Low dairy intake: May have insufficient K2
Vegans/vegetarians: Limited K2 sources
Cardiovascular Risk:
Heart disease family history: K2 prevents arterial calcification
High calcium supplementation: Need K2 to direct calcium properly
Diabetes: Higher cardiovascular and bone risks
Kidney disease: Risk of vascular calcification
Age-Related Factors:
Adults over 50: Increased bone loss and cardiovascular risk
Children/adolescents: For optimal bone development
Elderly: Higher needs due to reduced absorption
Dietary/Medical Factors:
Limited green vegetable intake: Low K1
No fermented foods: Low K2 intake
Malabsorption disorders: Celiac, Crohn's, cystic fibrosis
Long-term antibiotic use: Reduces gut K2 production
Gallbladder removal: Reduced fat digestion
Who Should AVOID or Use Caution
Absolute Contraindications:
Active Bleeding Disorders:
Recent stroke or bleeding: Any intracranial hemorrhage
Active GI bleeding: Ulcers, bleeding disorders
Upcoming surgery: Stop 1-2 weeks before major surgery
Blood Thinner Medications:
Warfarin users: Require medical supervision
Other anticoagulants: Consult physician first
Recent clot history: DVT, pulmonary embolism
Use Extreme Caution:
Cardiovascular Conditions:
Recent heart attack: Timing of supplementation matters
Atrial fibrillation on anticoagulants: Medical supervision required
History of stroke: Especially if on blood thinners
Liver Disease:
Severe hepatic impairment: Affects vitamin K metabolism
Cirrhosis: May have altered clotting factor production
Kidney Disease:
Advanced CKD: Risk of vascular calcification paradox
Dialysis patients: Complex calcium/phosphorus balance
Deficiency Symptoms
Vitamin K1 Deficiency (Rare in Healthy Adults):
Blood Clotting Issues:
Easy bruising: Minor trauma causes large bruises
Excessive bleeding: From cuts, dental work, surgery
Heavy menstrual bleeding: Prolonged or heavy periods
Nosebleeds: Frequent or difficult to stop
Blood in urine or stool: Internal bleeding
Laboratory Changes:
Prolonged PT/INR: Prothrombin time elevated
Prolonged aPTT: Partial thromboplastin time increased
Low clotting factors: Factors II, VII, IX, X reduced
Vitamin K2 Deficiency (More Common):
Bone Health Issues:
Increased fracture risk: Especially hip and spine
Low bone density: Osteopenia or osteoporosis
Slow bone healing: Delayed fracture repair
Dental problems: Increased cavities, weak teeth
Cardiovascular Issues:
Arterial calcification: Hardening of arteries
Increased heart disease risk: Silent progression
Reduced arterial elasticity: High blood pressure
Biochemical Markers:
Undercarboxylated osteocalcin: >20% indicates K2 deficiency
Inactive MGP: Matrix Gla protein not functioning
At-Risk Populations:
Newborns: All infants have low vitamin K at birth
Exclusively breastfed infants: Breast milk is low in K
People with malabsorption: Fat-soluble vitamin deficiency
Elderly in institutions: Limited fresh food access
Long-term antibiotic users: Reduced gut bacteria
People avoiding leafy greens: Dietary restriction
Toxicity Symptoms
Vitamin K1 and K2 (Natural Forms):
Virtually No Toxicity:
No upper limit established: Due to low toxicity risk
Large doses well-tolerated: Even 45 mg MK-4 daily
No adverse effects: In healthy individuals
Rare Reactions:
Allergic reactions: Skin rash, itching (very rare)
GI upset: At very high doses (>10 mg)
Synthetic Vitamin K3 (Menadione) - NOT Used in Supplements:
Highly Toxic:
Liver damage: Can cause hepatotoxicity
Hemolytic anemia: Destroys red blood cells
Banned in supplements: Due to toxicity risk
Interaction "Toxicity":
With Anticoagulants:
Clot formation: Risk if taking blood thinners
Not true toxicity: But can be dangerous
Requires monitoring: Medical supervision essential
Testing & Monitoring
Functional Tests:
Undercarboxylated Osteocalcin (ucOC):
Best K2 status marker: Reflects bone-specific K2 function
Normal: <20% of total osteocalcin
Deficiency: >20% undercarboxylated
Available: Specialty labs offer this test
Matrix Gla Protein (MGP) Tests:
Cardiovascular K2 function: Reflects arterial health
Less available: Research-focused testing
Emerging marker: May become more available
Blood Clotting Tests:
PT/INR (Prothrombin Time):
K1 deficiency: Prolonged clotting time
Normal range: INR 0.8-1.2 (not on anticoagulants)
Routine test: Available at all labs
When to Test:
Suspected deficiency: Bleeding or bone issues
Before supplementation: Baseline K2 status
On anticoagulants: Regular monitoring required
Monitoring progress: After 3-6 months supplementation
Special Considerations
Newborn & Infant Health:
Vitamin K Deficiency Bleeding (VKDB):
All newborns deficient: Placenta doesn't transfer K well
Standard treatment: K1 injection at birth
Breast milk low: In vitamin K content
Supplementation: May be needed for breastfed infants
Infant Supplementation:
Drops available: For breastfed babies
Dosing: 25 mcg daily typically recommended
Duration: Until solid foods introduced
Pregnancy & Breastfeeding:
Pregnancy Needs:
Adequate intake important: For fetal bone development
K2 particularly important: For proper calcium utilization
Safe supplementation: No known risks from natural forms
Avoid high doses: Stick to reasonable amounts
Breastfeeding:
Maternal K2 status: Affects breast milk content
Supplementation beneficial: May improve infant status
Monitor infant: For adequate vitamin K status
Age-Related Factors:
Children & Adolescents:
Bone development: Critical for peak bone mass
K2 especially important: For proper calcium deposition
Food sources preferred: Unless specific deficiency
Adults:
Maintenance: 100-200 mcg K2 daily optimal
Higher needs: If taking high-dose vitamin D or calcium
Elderly:
Increased needs: Due to reduced absorption and synthesis
Medication interactions: More likely on multiple drugs
Bone health priority: Fracture prevention critical
Athletic Performance:
Bone Stress:
High-impact sports: Increased bone turnover
May benefit: From K2 supplementation
With calcium/D3: Comprehensive bone support
No performance enhancement: Direct effects on athletic performance
K1 vs K2: The Critical Differences
Functional Specialization:
Vitamin K1:
Primary role: Blood clotting
Location: Concentrated in liver
Half-life: Hours
Sources: Green leafy vegetables
Vitamin K2:
Primary roles: Bone and cardiovascular health
Location: Distributed to tissues (bones, arteries, brain)
Half-life: Days to weeks
Sources: Fermented foods, animal products
Supplementation Strategy:
Don't rely on K1 alone: Won't provide K2 benefits K2 is the priority: For most health benefits beyond clotting MK-7 preferred: For convenience and effectiveness Both beneficial: Comprehensive approach best
Summary & Key Takeaways
Vitamin K is essential for blood clotting (K1) and directing calcium to bones while keeping it out of arteries (K2). Most people get adequate K1 from vegetables but are deficient in K2, which is found primarily in fermented foods and grass-fed animal products.
Optimal Approach:
Prioritize K2: Especially MK-7 form for bone and cardiovascular health
Partner with vitamin D3: Essential combination for calcium metabolism
Include magnesium: Completes the bone health trinity
Take with fat: Enhances absorption significantly
Be cautious with blood thinners: Requires medical supervision
Aim for 100-200 mcg K2 daily: For maintenance and prevention
Bottom Line: K2 is the more important form for most health benefits beyond blood clotting. MK-7 is the most practical supplemental form due to its long half-life. The combination of vitamin D3 + K2 + magnesium is one of the most important nutrient partnerships for bone and cardiovascular health. Anyone taking high-dose vitamin D or calcium supplements should definitely include K2.