Vitamin K Explained: K1 vs K2, How Much You Need, Food Sources and the Warfarin Warning
Most people meet their vitamin K needs from leafy greens alone — no supplement required.
You take vitamin D and calcium for your bones — so where does vitamin K fit?
If you have started reading supplement labels more carefully, vitamin K is the one that often causes a pause. It shows up next to vitamin D, it is mentioned whenever warfarin comes up, and it comes in two forms, K1 and K2, that sound similar but come from very different foods. It is easy to wonder whether you are missing something important, or whether a supplement could quietly interfere with a medication.
Here is the short answer first. Vitamin K is a fat-soluble vitamin your body needs to make proteins involved in blood clotting and bone metabolism. For adults 19 and older, the Adequate Intake (AI) is 120 micrograms (mcg) per day for men and 90 mcg per day for women, including during pregnancy and breastfeeding. Most healthy people reach that amount from food, especially leafy green vegetables. The one situation that needs real care is anticoagulant medication such as warfarin: if you take it, keep your vitamin K intake roughly the same every day and talk to your clinician before starting or stopping a vitamin K supplement. Sources: U.S. National Institutes of Health (NIH) Office of Dietary Supplements vitamin K fact sheets, cross-checked with Harvard T.H. Chan School of Public Health, The Nutrition Source.
What is vitamin K, in plain language?
A helper for clotting proteins
Think of vitamin K less like a building material and more like a switch. Several proteins that help blood clot normally are made in an inactive form, and vitamin K helps activate them. Without enough vitamin K, blood does not clot as it should. Vitamin K also plays a role in proteins involved in bone and tissue health, which is why it is often discussed alongside vitamin D and calcium — but that supporting role does not mean a supplement has been proven to prevent fractures or heart disease, and this guide does not claim that.
Why is it an Adequate Intake, not an RDA?
You will notice vitamin K recommendations are given as an AI rather than a Recommended Dietary Allowance (RDA). According to the NIH, the Food and Nutrition Board set AIs because there were not enough data to establish an Estimated Average Requirement and therefore an RDA. The AI is based on intakes seen in healthy groups and is assumed to ensure nutritional adequacy. That wording matters: 120 mcg and 90 mcg are practical daily targets from all sources, not a precise dose you must hit with a pill.
K1 vs K2: what is the difference?
Vitamin K1 (phylloquinone)
- Main form in the diet in North America
- Found mainly in green leafy vegetables such as kale, spinach, collard greens and turnip greens
- Also found in broccoli, Brussels sprouts, cabbage, lettuce, and soybean and canola oils
- This is the form in most standard vitamin K supplements in Canada and the United States
Vitamin K2 (menaquinones)
- A family of related compounds, including MK-4 and MK-7, which are named on some supplement labels
- Found in natto (fermented soybeans), and in smaller amounts in meat, cheese and eggs
- Some K2 is also produced by bacteria, including bacteria in the gut, although food remains the clearest source to plan around
For everyday eating, this distinction has a simple practical meaning. If you regularly eat leafy greens, you are mainly getting K1, and that alone can cover the AI. K2 products such as MK-7 are marketed heavily, but there is no separate established daily requirement for MK-4 or MK-7, and no official AI that says you need a specific amount of K2 on top of total vitamin K. If a label implies a precise K2 requirement, treat that as marketing language rather than an official standard.
Key points at a glance
- Adult AI: men 120 mcg/day, women 90 mcg/day (19+)
- Pregnancy and breastfeeding: 90 mcg/day
- No Tolerable Upper Intake Level (UL) has been set
- K1: leafy greens and some vegetable oils
- K2: natto, cheese, eggs, meat in smaller amounts
- On warfarin: consistency matters more than avoidance
How much vitamin K do you need each day?
A single generous serving of leafy greens can cover a full day's Adequate Intake.
Adequate Intakes by age
- Birth to 6 months: 2.0 mcg
- 7 to 12 months: 2.5 mcg
- 1 to 3 years: 30 mcg
- 4 to 8 years: 55 mcg
- 9 to 13 years: 60 mcg
- 14 to 18 years: 75 mcg
- Men 19 years and older: 120 mcg
- Women 19 years and older: 90 mcg
- Pregnancy and breastfeeding, 19 years and older: 90 mcg
These values are from the NIH Office of Dietary Supplements table of Adequate Intakes for vitamin K, and Harvard's Nutrition Source lists the same adult figures, which is the cross-check used for this guide.
Is there an upper limit?
The Food and Nutrition Board did not set a Tolerable Upper Intake Level (UL) for vitamin K, because of its low potential for toxicity and because adverse effects from vitamin K in food or supplements have not been reported in healthy people in the sources reviewed by the NIH. "No UL" does not mean "take as much as you like." It means researchers did not find a basis for a formal ceiling — and for anyone on an anticoagulant, the interaction issue below matters far more than toxicity.
Which foods are richest in vitamin K?
Leafy greens do most of the work
Leafy green vegetables are by far the richest common source. Raw spinach contains roughly 480 mcg per 100 grams in commonly used nutrition tables, and kale, collard greens, turnip greens and parsley are also very high. In practical terms, the NIH and Canadian nutrition guidance both note that a modest serving of greens — for example half a cup of cooked greens or a large salad — can meet or exceed the adult AI for that day. Broccoli, Brussels sprouts, green beans, cabbage and lettuce provide smaller but still useful amounts, and soybean and canola oils add vitamin K when used in cooking and dressings.
Where K2 shows up in food
Natto is the standout K2 food by a wide margin, but it is not a staple for most readers in Canada. Cheese, egg yolks and meats contain smaller, variable amounts of K2. You do not need to chase natto or buy a K2 supplement just to "complete" your intake if your total vitamin K from a varied diet already reaches the AI. If you enjoy fermented foods and cheese, count them as part of a varied pattern rather than as a prescription.
A realistic food-first day
- Breakfast: eggs with a handful of spinach cooked in a little oil
- Lunch: a salad with romaine, kale or mixed greens and a canola or soybean oil dressing
- Dinner: broccoli or Brussels sprouts beside your main dish
- Optional: a small serving of cheese or another fermented food you already enjoy
Because vitamin K is fat-soluble, eating greens with a source of fat — oil in cooking or dressing, for example — is a sensible general nutrition practice. You do not need a special timing ritual for vitamin K from food.
Should you take a vitamin K supplement?
In Canada, check for an eight-digit NPN on a supplement label — and check interactions before you check the price.
Most healthy adults eating greens probably do not need one
Deficiency in healthy adults who eat a varied diet is uncommon in the NIH summaries, in part because vitamin K is widespread in vegetables and oils. A supplement may be discussed in specific medical situations, but that is a clinician conversation, not a shopping decision. Multivitamins often contain a small amount of vitamin K, so check the total from all products you take rather than looking at one bottle in isolation.
The Canadian label check
In Canada, licensed natural health products carry an eight-digit Natural Product Number (NPN) on the label. An NPN tells you the product is licensed for sale as a natural health product in Canada; it does not prove a disease claim. Read the form (K1 or K2, and MK-7 if it is K2), the amount per capsule in mcg, and the directions and risk statements. If the amount is many times the AI, ask why you would need that amount before buying.
Who should talk to a clinician first?
- Anyone taking warfarin or a similar anticoagulant
- Anyone told they have a condition affecting fat absorption or liver or bile function
- Anyone taking antibiotics for a prolonged course, or other medicines flagged on the product's risk statements
- Parents considering any supplement for an infant or child — newborn vitamin K is a medical procedure at birth, not a home supplement decision
The warfarin warning, explained carefully
Why consistency matters
Warfarin (brand name Coumadin is the example the NIH uses) works by opposing vitamin K's role in clotting. The NIH warns that a sudden change in vitamin K intake can change how warfarin works: suddenly getting much less vitamin K can increase the risk of dangerous bleeding, while suddenly getting much more can increase the risk of clots by reducing the drug's effect. The practical advice is not "never eat greens." It is to keep the amount of vitamin K from food and supplements about the same every day, and to tell your care team before you start a vitamin K supplement, stop one, or make a major diet change such as a green-juice cleanse or a sudden switch to large daily salads.
If you take a newer anticoagulant that is not warfarin, do not assume the same rule applies in the same way — ask your pharmacist or prescriber how vitamin K affects your specific medicine. And never adjust a prescribed anticoagulant dose on your own because you changed your diet.
So, what should you actually do?
If you do not take an anticoagulant, the food-first answer is refreshingly simple: eat leafy greens and other vegetables regularly, use a variety of foods across the week, and you will very likely meet the 90 to 120 mcg AI without tracking every microgram. If you rarely eat greens, fixing that habit will do more for your overall diet than adding a single-nutrient pill. If you do take warfarin, keep your pattern steady, write down any supplement you use, and bring that list to every appointment.
Related reading on this blog
Do you get most of your vitamin K from salads and cooked greens, or is this a nutrient you had never thought about until a supplement label mentioned it? Share in the comments. Follow this blog to catch new evidence-based nutrition guides as soon as they are published — you can follow from the sidebar follower widget.
This article is general information only and is not medical advice. It does not diagnose, treat, or prevent any condition. Talk to a health care professional about your own situation, especially if you take anticoagulant medication, are pregnant or breastfeeding, or have a health condition.
Sources: U.S. National Institutes of Health (NIH) Office of Dietary Supplements, Vitamin K fact sheets for consumers and health professionals (Adequate Intakes: men 19+ 120 mcg, women 19+ 90 mcg, pregnancy and lactation 90 mcg; no UL established; warfarin interaction and consistency advice). Cross-checked with Harvard T.H. Chan School of Public Health, The Nutrition Source, Vitamin K (same adult AI values and K1/K2 food sources).
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