Vitamin K
Also known as: K1, Phylloquinone, Phytonadione, Vitamin K, vitamin-k
Overview
A fat-soluble vitamin essential for blood clotting, bone metabolism, and cardiovascular health. Phytonadione (K1) is the plant-derived form found in leafy greens and the primary supplemental form.
Frequently Asked About Vitamin K
How much Vitamin K should I take?
When is the best time to take Vitamin K?
Should I take Vitamin K with food?
What is the best form of Vitamin K?
Does Vitamin K interact with medications?
What does Vitamin K pair well with?
Who should not take Vitamin K?
Compare Forms
3 formsDifferent chemical forms vary in absorption, side effects, and best use cases. Higher bioavailability scores indicate better absorption.
K2 as MK-7 (Menaquinone-7)
HIGH 100Long-chain K2 from natto fermentation
💡 Excellent. Half-life of 3 days means once-daily dosing works.
- • Long half-life
- • Best vascular protection data
- • Synergizes with vitamin D
- • Expensive
- • Can interact with warfarin (avoid if on blood thinners)
📝 Best general K2 choice. Pair with vitamin D3 + magnesium.
K2 as MK-4 (Menatetrenone)
HIGH 90Short-chain K2; the form found in animal foods
💡 Good but very short half-life — requires multiple doses per day.
- • Strong bone-density evidence at high doses (45 mg/day)
- • May support testosterone
- • Multiple daily doses needed
- • Therapeutic doses are very high
📝 Less convenient than MK-7 for general use. Therapeutic role at 45 mg in osteoporosis.
K1 (Phytonadione/Phylloquinone)
GOOD 75Plant-form vitamin K, primarily for blood clotting
💡 Good with fat. Mostly retained by the liver; less reaches bones/arteries.
- • Cheapest
- • Found in leafy greens
- • Reliable for clotting
- • Limited extra-hepatic activity
- • Doesn't replace K2 for bone/vascular needs
📝 K2 is preferred for supplementation. Get K1 from leafy greens instead.
Dosage
Usually adequate from diet
Those on warfarin need consistent intake
Research & Studies
We haven’t curated landmark studies for Vitamin Kyet — one-click into the primary literature here. PubMed (RCTs) is usually the highest-signal starting point.
Mechanism of Action
- • Essential cofactor for clotting factors II, VII, IX, X
- • Rapidly cleared from circulation
- • Converts to MK-4 in some tissues
Evidence Quality
Essential for coagulation
Safety & Contraindications
- • CRITICAL: Reverses warfarin anticoagulant effect
- • Warfarin users must consult physician before use
- • Keep vitamin K intake consistent if on blood thinners
- • Warfarin users (without physician guidance)
- • Other vitamin K antagonist anticoagulants
- • Very safe
Consult healthcare provider
Safe
Interactions
- • Warfarin - must keep intake consistent
- • K2 preferred for bone/heart
- • Green vegetables
Stacking & Synergies
Buying Guide
- • Adequate dose
- • K2 preferred for bone/heart benefits
- • Abundant in diet
Top Products with Vitamin K
Highest-scored catalog products containing Vitamin K, ranked by our scoring engine.
Browse all Vitamin K products →
Related Guides
In-depth guides covering Vitamin K — protocols, comparisons, and use cases.
More in Vitamin
Other ingredients in the Vitamin category.
Cite this page
Formulate Research Team. (2026, June). Vitamin K — Evidence-Based Supplement Guide. Formulate Supplement Encyclopedia. https://app.formulate-health.app/learning/supplements/vitamin-k
Educational content based on published research and our scoring methodology. Not medical advice — consult a qualified healthcare provider before starting, stopping, or changing supplements, especially if you take medications, are pregnant, or have a medical condition.