If you take a multivitamin, a bone-health supplement, or a standalone vitamin K product, the label may list vitamin K in a form you don’t recognize — and if you’re on warfarin or a similar anticoagulant, that form and amount matter. This guide shows you how to read vitamin K on a supplement label, how it compares to what you get from food, and how to put together a simple list for a pharmacist or clinician conversation.
This article does not tell you to start, stop, or change any medication or supplement. If you take an anticoagulant, any change in your vitamin K intake — food or supplement — should go through your prescribing clinician or pharmacist.
Terms to Know Before You Read a Label
- Vitamin K1 (phylloquinone): The main form of vitamin K in plant foods, especially leafy greens and vegetable oils.
- Vitamin K2 (menaquinone): A family of forms found in fermented foods and some animal products, and made by bacteria in the gut. Supplement labels often list this as MK-4 or MK-7.
- Phytonadione: A synthetic version of vitamin K1 sometimes used in supplements.
- Anticoagulant: A medication that reduces the blood’s ability to clot, often called a “blood thinner.” Warfarin (Coumadin) is the most common vitamin K-related example.
- Vitamin K antagonist: The drug class that includes warfarin. These medications work by interfering with how the body uses vitamin K, so a sudden increase or drop in vitamin K intake can affect how the medication performs.
- INR / Prothrombin time (PT): Blood tests used to monitor how well an anticoagulant is working. Your clinician uses these results, not the supplement label, to judge your status.
- Adequate Intake (AI): The vitamin K reference amount for healthy adults — 120 micrograms (mcg) a day for men 19 and older, according to the National Institutes of Health Office of Dietary Supplements (ODS).
Why the Form and Amount on a Label Matters
Vitamin K helps the body build proteins involved in blood clotting. According to the NIH Office of Dietary Supplements Vitamin K fact sheet, warfarin and related anticoagulants work by interfering with how the body uses vitamin K — which is why a steady, consistent intake matters more than a “high” or “low” one for people on these medications. A sudden jump or drop in vitamin K, whether from food or a supplement, can shift how the medication performs.
Most standard multivitamins contain vitamin K at under 75% of the daily reference amount, per the ODS fact sheet. But standalone vitamin K supplements — sold alone or paired with calcium, magnesium, or vitamin D — can run far higher, with some products providing over 4,000 mcg, more than 30 times the adult male AI. That range is exactly why reading the actual label amount matters more than assuming “it’s just a vitamin.”
Vitamin K1 vs. Vitamin K2: What’s Actually on the Label
Supplement labels don’t always use the same wording as food nutrition guides. Here’s how the two main label forms compare, based on the ODS fact sheet:
- Vitamin K1 / phylloquinone / phytonadione: The most common food-derived form. On a supplement label, this may appear as “vitamin K1,” “phylloquinone,” or “phytonadione” (a synthetic version). This form is most directly tied to the interaction warnings clinicians give warfarin patients.
- Vitamin K2 / MK-4: A menaquinone form found in some animal-based foods and produced by the body from K1. Supplements may separately list this as “MK-4.”
- Vitamin K2 / MK-7: A longer-acting menaquinone form, often sourced from natto (fermented soybeans) in supplement manufacturing. Research cited by ODS suggests MK-7 stays in the body longer than phylloquinone, though bioavailability data for all forms remains limited.
- What’s not used anymore: Menadione (sometimes called “vitamin K3”) was linked to liver cell damage in older laboratory studies and, per ODS, is no longer used in dietary supplements or fortified foods in the U.S.
Food Sources Worth Knowing
Most of a man’s vitamin K intake comes from food, not supplements. Per ODS data, U.S. men average about 138 mcg a day from food alone — already above the 120 mcg AI. Foods highest in vitamin K1 include:
- Collard greens and turnip greens (frozen, boiled): over 400% of the daily value per half-cup serving
- Spinach (raw): about 121% of the daily value per cup
- Kale (raw) and broccoli (boiled): both around 90–95% of the daily value per serving
- Soybean and canola oil: smaller but consistent contributions per tablespoon
- Natto (fermented soybeans): very high in vitamin K2 (MK-7) specifically — over 700% of the daily value per 3-ounce serving
Clinicians ask about “consistent” vitamin K intake, rather than “low” intake, because a diet with regular greens is normal and expected—the goal for someone on an anticoagulant is to keep that pattern steady, not eliminate vitamin K-rich foods.
A Field Guide: Building Your Total-Intake Worksheet
Use this sequence to prepare for a pharmacist or clinician conversation, especially if you’re on warfarin or a similar medication, or your clinician has asked you to track vitamin K.
- Step 1 — List every supplement source. Check your multivitamin, any bone or joint formula, and any standalone vitamin K, calcium, or D3 product for a “Vitamin K” line on the Supplement Facts panel.
- Step 2 — Record the exact amount and form for each. Write down the mcg amount and whether it’s listed as K1, phylloquinone, phytonadione, MK-4, or MK-7. Add them together for a rough daily supplement total.
- Step 3 — Note your regular food pattern. You don’t need to weigh vegetables. Just note whether you eat leafy greens, natto, or vegetable oils daily, a few times a week, or rarely — that pattern matters more to your clinician than a single day’s intake.
- Step 4 — Flag any recent changes. New supplements, a diet change, or a shift toward or away from greens in the past few weeks is exactly the kind of change your clinician needs to know about before your next INR check.
- Step 5 — Bring the full list to your appointment. Combine this worksheet with your current medication list — the NIH ODS fact sheet notes that antibiotics, bile acid sequestrants (like cholestyramine), and orlistat can also affect vitamin K status or interact with anticoagulants.
- Step 6 — Ask directly. A useful question for your pharmacist or prescriber: “Based on what I’m taking and eating, does anything here need to change, or just stay consistent?” Let them make that call — this worksheet is for the conversation, not a decision on its own.
When to Contact Your Clinician Promptly
If you’re on an anticoagulant and notice unusual bruising, bleeding that doesn’t stop as expected, blood in urine or stool, or unusually heavy nosebleeds, contact your prescribing clinician promptly. For severe or uncontrolled bleeding, seek emergency care right away.
The Bigger Interaction Picture
Vitamin K and anticoagulants are one well-known example, but they’re not the only supplement-medication pairing worth checking. The FDA’s consumer update on mixing medications and dietary supplements notes that other common supplements — including fish oil, vitamin E, and certain herbal products — can also affect how blood-thinning medications work, and that combining “natural” products with prescription drugs is not automatically safe. If you’re managing blood pressure or cholesterol medications alongside supplements, our guides on supplement interactions with blood pressure medications and statin and cholesterol medication interactions cover the same kind of full-picture check. If you’re comparing what’s actually in a general multivitamin, including vitamin K content, see our breakdown of what men’s multivitamins typically contain.
Educational Disclaimer
This article is for general educational purposes only and is not medical advice. It is not a substitute for a conversation with your doctor, pharmacist, or other qualified health care provider, and you should not use it to start, stop, or adjust any medication or supplement. Only your prescribing clinician, using your specific health history and lab results, can determine what’s appropriate for you.
By VFM Research Desk. Updated September 14, 2026. Sources: National Institutes of Health, Office of Dietary Supplements, Vitamin K — Health Professional Fact Sheet; U.S. Food and Drug Administration, “Mixing Medications and Dietary Supplements Can Endanger Your Health.”