This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your physician or qualified healthcare provider before starting any supplement regimen.
Vitamin K is often treated as a single nutrient, but K1 (phylloquinone) and K2 (menaquinone) serve meaningfully different functions in the body. Most people get plenty of K1 from leafy greens, yet K2 deficiency is widespread — and its consequences for bone and cardiovascular health are significant.
Here is why this distinction matters and which form you should be supplementing.
Vitamin K1 (Phylloquinone): Overview
Vitamin K1 is found abundantly in green leafy vegetables — kale, spinach, broccoli, and Brussels sprouts. It is the form most responsible for activating clotting factors in the liver.
Key Benefits
- Blood Clotting: K1 is essential for synthesizing clotting factors II, VII, IX, and X. Without it, even minor cuts could lead to dangerous bleeding.
- Easy to Obtain Through Diet: A single cup of cooked spinach provides over 800% of the daily recommended intake of vitamin K.
- Immediate Liver Uptake: K1 is rapidly absorbed by the liver where clotting factors are produced.
Typical Dosage
The adequate intake is 90 mcg/day for women and 120 mcg/day for men, easily met through a diet rich in green vegetables.
Vitamin K2 (Menaquinone): Overview
Vitamin K2 exists in several subtypes — the most important are MK-4 (found in animal products) and MK-7 (produced by bacterial fermentation, highest in natto). Unlike K1, vitamin K2 circulates in the bloodstream longer and reaches tissues beyond the liver, including bones and arteries.
Key Benefits
- Directs Calcium to Bones: K2 activates osteocalcin, a protein that binds calcium into bone matrix. A 3-year Japanese trial found MK-7 supplementation significantly reduced bone loss in postmenopausal women.
- Protects Arteries from Calcification: K2 activates matrix GLA protein (MGP), which prevents calcium from depositing in artery walls. The Rotterdam Study found that high K2 intake was associated with a 52% reduction in arterial calcification.
- Synergy with Vitamin D: Vitamin D increases calcium absorption, while K2 ensures that calcium goes to your bones rather than your arteries. This is why vitamin D and K2 are frequently recommended together.
Typical Dosage
100–200 mcg of MK-7 per day, or 1,000–5,000 mcg of MK-4. MK-7 is preferred for supplementation because its longer half-life (~72 hours vs. ~6 hours for MK-4) allows once-daily dosing.
Head-to-Head Comparison
| Factor | Vitamin K1 | Vitamin K2 (MK-7) | |--------|-----------|-------------------| | Primary function | Blood clotting (liver) | Calcium direction (bones and arteries) | | Food sources | Leafy greens (kale, spinach) | Natto, egg yolks, hard cheeses, organ meats | | Dietary adequacy | Most people get enough | Most people are deficient | | Half-life | 1–2 hours | ~72 hours (MK-7) | | Reaches beyond liver | Minimally | Yes — bones, arteries, soft tissues | | Bone health evidence | Limited | Strong (reduced bone loss in trials) | | Heart health evidence | Limited | Strong (reduced arterial calcification) | | Cost (30-day supply) | $5–$10 | $10–$20 | | Best For | Blood clotting support (rarely needs supplementing) | Bone density, arterial health, vitamin D pairing |
The Verdict
Supplement Vitamin K2 (MK-7), not K1. Almost everyone gets enough K1 from food, but K2 deficiency is common and has serious consequences for bone density and cardiovascular health. If you take vitamin D — and most health professionals recommend you should — adding 100–200 mcg of MK-7 is a smart insurance policy to ensure calcium goes where it belongs.
The only reason to supplement K1 is if you are on a severely restricted diet that excludes green vegetables, which is rare.
Important note for people on blood thinners: Vitamin K (both forms) can interfere with warfarin and similar medications. Always consult your doctor before supplementing K1 or K2 if you take anticoagulants.
Track Your Choice
Since K2 works gradually to improve bone density and arterial health, consistent daily intake over months is essential. Use Supplement Tracker to log your K2 alongside vitamin D and track your bone health markers over time.
