vitamin
Vitamin K1 vs K2: Forms, Foods and Warfarin
Also known as vitamin K1, vitamin K2, phylloquinone, phytonadione, menaquinone, MK-7, MK-4, vitamin K2 MK-7
Short answer
Vitamin K is a fat-soluble vitamin the body needs to make proteins for blood clotting and bone metabolism. K1 (phylloquinone) comes mainly from leafy greens; K2 (menaquinones such as MK-4 and MK-7) comes from fermented and animal foods. If you take warfarin, keep vitamin K intake steady and ask your pharmacist before taking a supplement [1].
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What is Vitamin K (K1 and K2)?
Vitamin K is the name for a family of fat-soluble compounds: phylloquinone (vitamin K1) and the menaquinones (vitamin K2), such as MK-4 and MK-7 [1]. The body uses it as a coenzyme to make proteins involved in blood clotting, such as prothrombin, and in bone metabolism, such as osteocalcin [1]. Gut bacteria also make menaquinones [1]. The body breaks vitamin K down quickly, so blood levels and stores are low [1].
Forms of Vitamin K (K1 and K2) you'll see on labels
Vitamin K1 (phylloquinone or phytonadione)
The main form in the diet, found mostly in leafy green vegetables. Phytonadione is the synthetic K1 used in supplements [1].
Vitamin K2 as MK-7
Found in high amounts in natto. One study found both phytonadione and MK-7 supplements are well absorbed, but MK-7 stays in the body longer (longer half-life) [1].
Vitamin K2 as MK-4
The body makes MK-4 from K1. It is found in small amounts in meat, eggs and dairy [1].
Menadione (vitamin K3)
A synthetic form that damaged liver cells in lab studies. It is no longer used in supplements or fortified foods [1].
How much Vitamin K (K1 and K2) do adults need?
NIH lists these Adequate Intakes (AI) for adults 19+, in micrograms (mcg). Reference values, not a personal recommendation.
| Group | Amount per day |
|---|---|
| Men 19+ | 120 mcg |
| Women 19+ | 90 mcg |
| Pregnancy 19+ | 90 mcg |
| Lactation 19+ | 90 mcg |
Upper limit: No UL has been set, because vitamin K has a low potential for toxicity [1]. In the UK, the NHS says 1 mg (1,000 mcg) or less a day from supplements is unlikely to cause harm [2].
How Vitamin K (K1 and K2) appears on a label
Vitamin K is listed in mcg. The Daily Value (DV) used for % DV is 120 mcg for adults and children 4 and older [1]. Labels should say the form: K1 as phylloquinone or phytonadione, or K2 as MK-4 or MK-7 [1]. Multivitamins usually contain less than 75% DV, while vitamin K-only or combination products (often with calcium, magnesium or vitamin D) can be much higher [1].
When to take Vitamin K (K1 and K2)
No official source names a best time of day to take vitamin K. NIH notes that eating vegetables with some fat helps the body absorb more K1 from them [1]. If you take warfarin, NIH says what matters is keeping your vitamin K intake consistent from day to day [1].
What to keep apart from Vitamin K (K1 and K2)
Warfarin (Coumadin) and similar anticoagulants
Vitamin K can have a serious, potentially dangerous interaction with warfarin. Sudden changes in vitamin K intake can raise or lower its effect, so people on warfarin need consistent vitamin K intake from food and supplements [1]. Ask your pharmacist or doctor before starting or stopping a vitamin K supplement.
Antibiotics
Antibiotics can kill the gut bacteria that make vitamin K, especially cephalosporins. NIH says supplements are usually not needed unless antibiotic use lasts several weeks and diet is poor [1]. Ask your pharmacist.
Bile acid sequestrants (cholestyramine, colestipol)
These can reduce absorption of vitamin K and other fat-soluble vitamins [1]. Ask your pharmacist.
Orlistat
Orlistat reduces fat absorption, which can lower vitamin K absorption. Combined with warfarin it might significantly change clotting time [1]. Ask your pharmacist.
Vitamin D and calcium
Many vitamin K supplements combine it with calcium, magnesium or vitamin D [1]. NIH does not give a rule for taking them together.
Foods that contain Vitamin K (K1 and K2)
- Natto (fermented soybeans, K2 as MK-7)
- Collard greens
- Turnip greens
- Spinach
- Kale
- Broccoli
- Soybeans and soybean oil
- Canola oil
- Iceberg lettuce
- Cheese and other fermented foods (K2)
Who should ask a doctor or pharmacist first
If you take warfarin or a similar anticoagulant, talk to your pharmacist or doctor before taking any vitamin K supplement or changing how much leafy green food you eat [1]. Also ask first if you take long-term antibiotics, bile acid sequestrants or orlistat, or if you have a condition that affects fat absorption, such as cystic fibrosis, celiac disease or ulcerative colitis, or have had bariatric surgery [1].
Keep Vitamin K (K1 and K2) in a routine that fits
Supin schedules what you take by time of day, reminds you, and tells you when a bottle runs low.
Vitamin K (K1 and K2): questions people ask
Sources
- Vitamin K: Fact Sheet for Health Professionals — NIH Office of Dietary Supplements
- Vitamin K - Vitamins and minerals — NHS
Educational information, not medical advice. The amounts above are official reference values, not a recommendation for you. Check with your doctor or pharmacist before starting or changing supplements, especially if you take medication, are pregnant or have a health condition. Supin sells a subscription, not supplements. Last reviewed .