What is Vitamin K1?
A fat-soluble vitamin essential for blood clotting, found primarily in leafy greens.
Vitamin K1 (phylloquinone) is the primary dietary form, abundant in green leafy vegetables. It activates clotting factors. Unlike K2, it has limited effects on calcium metabolism. Deficiency is rare in adults but can occur with malabsorption or antibiotic use.
What the evidence says
The overall evidence grade for Vitamin K1 is A (strong — consistent, high-quality human evidence (systematic reviews, well-powered RCTs)). Essential for blood clotting. Role well-established.
Specific findings with supporting evidence:
- Essential for blood clotting. Evidence grade A.
- Found abundantly in leafy greens. Evidence grade A.
Best-supported outcomes:
- Blood clotting function.
- Hemorrhage prevention.
Where marketing outpaces evidence:
- Marketing often overstates: Bone benefits (K2 is more relevant).
- Marketing often overstates: Cardiovascular benefits.
Dose and timing
The typical effective dose for Vitamin K1 is 90–120 mcg. No established upper limit.
Take it in the morning and afternoon with a fat-containing meal. Fat-soluble.
Who it's for, and who should skip it
Most relevant for:
- Those with malabsorption.
- People on long-term antibiotics.
Not appropriate for:
- Those on warfarin without medical guidance.
Safety and cautions
Important: Warfarin interaction. K1 directly counteracts warfarin. Maintain consistent intake if on this medication.
Common mistakes
- Confusing K1 with K2 benefits.
- Varying intake dramatically while on warfarin.
- Supplementing without need.
Myths vs reality
A common misconception: K1 and K2 are interchangeable. In reality, k1 primarily affects clotting; K2 affects calcium metabolism.
How it interacts with other compounds
- Vitamin K1 works well alongside vitamin k2 — different roles; K2 for calcium, K1 for clotting.
Questions people ask
Do I need to supplement K1? Most people get enough from vegetables. Deficiency is rare.
Editorial note
This guide summarizes the published evidence on Vitamin K1. It is educational content, not medical advice. Confirm with your clinician if you take prescription medications or manage a chronic condition.