K1 is the dietary clotting form from greens; K2 is more studied for directing calcium into bone. For most people a greens-rich diet covers K1.

Do I need to supplement K1?

Rarely — vegetables provide ample amounts, so deficiency is uncommon outside specific medical situations.

Is it safe with warfarin?

Keep intake consistent and coordinate with your provider — vitamin K directly opposes warfarin's action.

Vitamin K1: Benefits, Dosing & Evidence

What it is

Vitamin K1 is the form found in leafy greens and is your body's main dietary source of vitamin K, essential for normal blood clotting and a role in bone.

How it works

Vitamin K1 (phylloquinone) from plants is your main dietary source of vitamin K, essential for activating the proteins that let blood clot normally, plus a supporting role in bone. Most is used by the liver for clotting factors.

What it's been studied for

Used to support normal clotting and bone health, mainly where intake is low.

What the evidence shows

K1 is essential and most people get enough from vegetables. For bone specifically, K2 has been more studied. Deficiency is uncommon outside certain medical situations.

Who should consider it

Deficiency is uncommon outside specific medical situations, since greens supply plenty. For bone specifically, K2 has been studied more. Anyone on warfarin must keep vitamin K intake consistent and coordinate with their provider.

Amounts commonly studied

Daily needs are around 90-120 mcg, usually met by diet.

How to take it

Daily needs (about 90-120 mcg) are usually met by diet. It's fat-soluble, so any supplement is taken with a meal. It's distinct from K2, which is emphasized for bone.

Forms & absorption

K1 (phylloquinone) from plants; distinct from K2 (menaquinone), which is emphasized for bone.

Food sources

Leafy greens (kale, spinach, collards), broccoli, Brussels sprouts, and vegetable oils.

Safety & interactions

Safe from food and supplements. Critical exception: vitamin K interacts with warfarin (a blood thinner), so anyone on it must keep intake consistent and coordinate with their provider.

Myths & what it won't do

Myth: vitamin K supplements are dangerous for everyone on blood thinners. Reality: the critical interaction is with warfarin specifically; newer anticoagulants differ — but always confirm with your provider. Myth: K1 and K2 are interchangeable. Reality: they have overlapping but distinct roles.

Common questions

K1 or K2?: K1 is the dietary clotting form from greens; K2 is more studied for directing calcium into bone. For most people a greens-rich diet covers K1.
Do I need to supplement K1?: Rarely — vegetables provide ample amounts, so deficiency is uncommon outside specific medical situations.
Is it safe with warfarin?: Keep intake consistent and coordinate with your provider — vitamin K directly opposes warfarin's action.

The amounts listed here are what published research has used — not a prescription or a recommended dose for you. Confirm anything you plan to take with your own healthcare provider, especially if you take medications, are pregnant or nursing, or have a health condition.

Vitamin K1