Vitamin K1 (Phylloquinone)
Supplements · Vitamins · Supplement, Typed Supps
A fat-soluble vitamin your body needs to make blood clot properly — well proven for that, less proven for the bone and heart claims often pinned on it.
Stage by stage
- Intake (Capsule or softgel): Best taken with a meal containing some fat.
- Small intestine (Absorbed): Absorbed alongside dietary fat via bile-dependent micelle formation.
- Liver (Activated): Used as a cofactor to activate several blood-clotting factors.
- Bloodstream (Circulates): Activated clotting factors circulate, ready for normal coagulation.
What the evidence supports
- Supporting normal blood clotting by activating clotting factors made in the liver — strong evidence. This is vitamin K’s core, well-established biological role — it’s a required cofactor for the liver enzyme that activates several clotting factors, and deficiency reliably causes bleeding problems.
- Improving bone density or reducing arterial calcification when taken specifically as vitamin K1 — limited evidence. Most of the stronger bone- and heart-related vitamin K research uses K2 (menaquinones, especially MK-7), which behaves differently in the body than K1. Evidence for K1 supplementation specifically improving bone or vascular outcomes is thinner and less consistent.
- Evidence on Reducing the effectiveness of warfarin and other vitamin K antagonist blood thinners — strong evidence. This interaction is well documented and clinically significant — changes in vitamin K intake, from food or supplements, can meaningfully shift INR values in people on these medications.
Typical dose
Supplemental doses commonly range 100–500 mcg/day, though this is well above what most people need from diet alone
Upper limit: No established UL — no toxicity has been documented at high phylloquinone intakes
Timing
Take with a fat-containing meal for best absorption.
Time to effect
- Days: Clotting-factor activity can shift within days of a change in vitamin K intake.
Common myth
“Vitamin K is basically the same whether it’s K1 or K2, so any form covers bone and heart health.” In reality: K1 (phylloquinone) is the form with strong evidence for normal blood clotting; the bone and cardiovascular research is largely specific to K2 (menaquinones), which the body handles differently.
Food sources
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