Vitamin K1

Q: Is Vitamin K1 deficiency common?

No -- true vitamin K deficiency is uncommon in adults eating a varied diet with vegetables, since the body also recycles vitamin K efficiently and gut bacteria contribute some supply. Deficiency is more of a concern in newborns (who receive a standard vitamin K shot at birth), people with fat-malabsorption conditions, or those on long-term antibiotics or certain medications that interfere with vitamin K.

The plant-based form your body relies on most directly for normal blood clotting

Essential for activating clotting factors

Deficiency is rare with a normal, varied diet

Important: These statements have not been evaluated by the FDA. This information is not intended to diagnose, treat, cure, or prevent any disease. Anyone taking warfarin or other blood thinners must talk to their doctor before changing vitamin K intake in any form.

Overview

Vitamin K1, or phylloquinone, is the primary dietary form of vitamin K and the form your liver uses most directly to activate the clotting factors that let blood coagulate normally. It's found abundantly in green leafy vegetables like kale, spinach, and collard greens, along with broccoli and certain vegetable oils, which is why true dietary deficiency is uncommon in adults eating a reasonably varied diet.

K1 is distinct from vitamin K2 (menaquinone), which comes mainly from fermented foods and animal products and is more associated with bone and cardiovascular research specifically. Both forms support the same underlying vitamin K-dependent proteins, but K1's clearest, best-established role remains blood clotting — this is also the reason vitamin K carries one of the more serious drug-interaction warnings of any common nutrient, since it directly opposes how warfarin and similar blood thinners work.

Potential Benefits

Normal Blood Clotting

Required for the liver to activate clotting factors II, VII, IX, and X — without adequate K1, the body can't form clots properly.

Widely Available From Whole Foods

Abundant in leafy greens, making dietary sufficiency achievable for most people without supplementation.

Supports Vitamin K-Dependent Proteins

Contributes to the activation of additional proteins beyond clotting factors, including some involved in bone and tissue mineralization.

Well-Established Safety at Dietary Levels

No established toxicity from vitamin K1 at typical dietary or supplemental doses in people not on blood-thinning medication.

Typical Dosage

Standard Adequate Intake

90–120mcg per day

Adequate Intake level for adult women and men, respectively, achievable through diet alone for most people

When Supplementation Is Considered

Fat-malabsorption conditions or very low vegetable intake

Best discussed with a doctor rather than self-supplemented, especially given the blood-thinner interaction

Pro Tips

If you're on warfarin, keep your vitamin K intake consistent day to day rather than avoiding it entirely — sudden swings are what disrupt INR control
Take with a meal containing some fat, since vitamin K is fat-soluble and absorbs better that way
Most healthy adults eating vegetables regularly don't need a separate K1 supplement
If bone or cardiovascular support is the actual goal, K2 has the more specific research base for that use case

Research Snapshot

A comprehensive review of vitamin K's sources, physiological role, and clinical use confirms that phylloquinone (K1) is required for the post-translational activation of seven proteins involved in blood coagulation, and that true dietary deficiency in adults is uncommon given typical vegetable intake, the body's ability to recycle vitamin K, and contribution from gut bacteria. The review also details vitamin K's central role in the mechanism of action of warfarin-type anticoagulants, underscoring why consistent — not necessarily low — intake matters most for patients on those medications.

Source: Mladěnka et al., Nutrition Reviews (2022)

How Vitamin K1 Compares

Ingredient	Best For	Key Difference
Vitamin K1	Blood Clotting	Plant-based, the primary form your body uses for coagulation
Vitamin K2	Bone & Cardiovascular Support	Longer circulation time, more specific research on calcium direction
Vitamin D3	Bone Health, Immune Support	Often paired with K2 specifically for calcium regulation
Calcium	Bone Structure	The mineral vitamin K helps direct toward bone rather than soft tissue

These are the most common comparisons our customers ask about in-store.

Popular Stacks with Vitamin K1

Bone Health Stack

Vitamin K1 + Vitamin D3 + Calcium

A foundational combination for supporting bone mineralization

Complete Vitamin K Stack

Vitamin K1 + Vitamin K2

Covers both the clotting-focused and calcium-direction roles of vitamin K

Whole-Food Nutrient Stack

Vitamin K1 + Fiber + Magnesium

Rounds out common gaps for those who eat few leafy greens

Frequently Asked Questions

What's the difference between Vitamin K1 and Vitamin K2?

K1 (phylloquinone) is the plant-based form found in leafy greens and is the primary form your body uses for blood clotting. K2 (menaquinone) comes mainly from fermented foods and animal products, stays in circulation longer, and is more associated with directing calcium toward bones and away from arteries. Most people get sufficient K1 from a normal diet with vegetables; K2 is the form more often discussed for bone and cardiovascular support specifically.

Can I take Vitamin K1 if I'm on blood thinners?

Not without your doctor's guidance. Vitamin K works directly against how warfarin and similar blood thinners function, since the drugs work specifically by blocking vitamin K's clotting activity. Sudden changes in vitamin K intake, from food or supplements, can meaningfully affect INR levels and blood-thinner dosing, so anyone on these medications should keep their vitamin K intake consistent and loop in their prescriber before supplementing.

Is Vitamin K1 deficiency common?

No — true vitamin K deficiency is uncommon in adults eating a varied diet with vegetables, since the body also recycles vitamin K efficiently and gut bacteria contribute some supply. Deficiency is more of a concern in newborns (who receive a standard vitamin K shot at birth), people with fat-malabsorption conditions, or those on long-term antibiotics or certain medications that interfere with vitamin K.

Sources & References

1. Mladěnka, P., Macáková, K., Kujovská Krčmová, L., et al. (2022). Vitamin K – sources, physiological role, kinetics, deficiency, detection, therapeutic use, and toxicity. Nutrition Reviews, 80(4), 677–698.

All references are peer-reviewed studies or position stands from reputable organizations.