Vitamin K is a fat-soluble vitamin critical for multiple bodily functions, most notably blood coagulation and bone metabolism. It exists in two main forms—vitamin K₁ (phylloquinone) and vitamin K₂ (menaquinones)—which differ in dietary sources, physiological roles, and emerging health benefits.
What Is Vitamin K?
Vitamin K₁ predominates in green leafy vegetables and plant oils, whereas vitamin K₂ comprises several subtypes (MK-4 through MK-13) produced by gut bacteria and found in fermented and animal foods. Together, they serve as cofactors for enzymes that activate vitamin K–dependent proteins involved in:
- Coagulation (Factors II, VII, IX, X)
- Bone mineralization (osteocalcin)
- Vascular health (matrix Gla protein)
Dietary Sources & Food Content
Foods High in Vitamin K₁ (per 100 g)
Note: Although certain herbs (e.g., basil, thyme) list very high levels, typical culinary usage involves much smaller quantities.
- Cooked collard greens – 623.2 µg
- Cooked mustard greens – 592.7 µg
- Raw Swiss chard – 830 µg
- Raw dandelion greens – 778.4 µg
- Cooked spinach – 540.7 µg
- Raw cress – 541.9 µg
- Cooked turnip greens – 518.9 µg
- Cooked beet greens – 484 µg
- Cooked kale – 418.5 µg
- Endives – 231 µg
- Cooked Brussels sprouts – 193.5 µg
- Broccoli – 141.1 µg
- Red leaf lettuce – 140.3 µg
- Green leaf lettuce – 126.3 µg
- Raw arugula – 108.6 µg
- Cooked cabbage – 108.7 µg
- Soybean oil – 183.9 µg
- Mayonnaise – 163 µg
- Margarine – 101.3 µg
Herbs & Spices (very high, but used sparingly):
- Dried basil – 1714.5 µg
- Dried sage – 1714.5 µg
- Dried thyme – 1714.5 µg
- Fresh parsley – 1640 µg
- Dried coriander leaf – 1359.5 µg
- Dried marjoram – 621.7 µg
- Dried oregano – 621.7 µg
- Chives – 212.7 µg
Foods High in Vitamin K₂ (per 100 g)
- Natto (fermented soybeans) – 939 µg
- Soft cheese (e.g., Brie) – 506 µg
- Blue cheese – 440 µg
- Hard cheese (e.g., Gouda) – 282 µg
- Goose liver – 369 µg
- Beef liver – 106 µg
- Full-fat milk – 38.1 µg
- Chicken meat – 35.7 µg
- Turkey frankfurter – 31.2 µg
Vitamin K₁ (Phylloquinone)
Functions
- Blood Clotting: Essential cofactor for γ-carboxylation of clotting factors II, VII, IX, and X, enabling effective blood clot formation.
- Bone Health: Participates in activation of osteocalcin, which binds calcium into the bone matrix.
Health Benefits
- Hemostasis: Prevents excessive bleeding.
- Bone Strength: Supports bone mineral density and reduces fracture risk.
- Cardiovascular: Epidemiological data link higher K₁ intake to lower all-cause and cardiovascular mortality.
Side Effects & Interactions
- Warfarin Interaction: High or inconsistent intake can alter anticoagulant efficacy—patients should maintain consistent K₁ consumption.
- Hypersensitivity (IV use): Rare anaphylaxis or hypotension with injectable phytonadione.
- No Toxicity from Diet: No Tolerable Upper Intake Level established for dietary K₁.
Vitamin K₂ (Menaquinones)
Functions
- Bone Metabolism: Activates osteocalcin, improving calcium incorporation into bone.
- Vascular Health: Activates matrix Gla protein, inhibiting arterial calcification.
Health Benefits
- Osteoporosis Prevention: MK-7 supplementation improves bone mineral density and reduces fracture risk in postmenopausal women.
- Heart Protection: Each 10 µg/day increment in dietary K₂ may reduce coronary heart disease risk by ~9 %.
- Emerging Roles: Potential benefits in insulin sensitivity, joint health, and cognitive function pending further research.
Side Effects & Interactions
- Warfarin Interaction: Sudden increases can alter anticoagulant effects—patients on blood thinners should consult healthcare providers before supplementing.
- Gastrointestinal Discomfort: Rare reports with high-dose supplements.
- No Toxicity from Diet: No upper limit for dietary K₂; supplements generally well tolerated.
Recommended Intakes
- Adults: 90 µg/day (women), 120 µg/day (men) total vitamin K.
- Newborns: Single 0.5–1 mg IM injection of K₁ at birth to prevent hemorrhagic disease.
Vitamins K₁ and K₂ are indispensable for maintaining healthy blood clotting, strong bones, and cardiovascular integrity. A balanced diet rich in leafy greens, fermented foods, cheeses, and certain animal products typically meets requirements. Individuals on anticoagulants should monitor intake consistency. Those at risk of osteoporosis or arterial calcification may consider K₂-rich foods or supplements under medical guidance.
-Nguyễn Duy Khiêm-
Sources for Further Reading
- NIH Office of Dietary Supplements. Vitamin K—Consumer Fact Sheet.
- Cleveland Clinic. What To Know About Vitamin K2 and Its Health Benefits.
- Healthline. Everything You Need to Know About the Vitamin K2.
- MedlinePlus. Vitamin K.