Reviewed and updated: 24 July 2026
Vitamin K2 as MK-7 is the long-chain menaquinone form of vitamin K2 that has become the preferred choice in supplements, because it is well absorbed and stays in circulation longer than shorter-chain forms. In this guide I will explain what MK-7 is, how it differs from K1 and MK-4, why it is paired with vitamin D3, how much to take, and the important warfarin interaction. For a buyer's guide, see how to choose a vitamin D3 and K2 supplement.
TL;DR: vitamin K2 MK-7 in brief
- What it is: menaquinone-7, a long-chain form of vitamin K2.
- Why it is used: good absorption and a longer circulating time than short-chain MK-4.
- What K does: vitamin K contributes to the maintenance of normal bones and to normal blood clotting.
- Why paired with D3: the two have complementary roles in bone health.
- Key caution: vitamin K can interfere with anticoagulant medicines such as warfarin.
K1 and K2: two branches of the vitamin K family
Vitamin K comes in two main forms. Vitamin K1 (phylloquinone) is found in leafy greens and is the form most associated with normal blood clotting. Vitamin K2 (menaquinone) is a family of related forms found in fermented foods and some animal products, written as MK-4, MK-7 and so on. The number refers to the length of the molecule's side chain, and that length changes how the form behaves in the body.
What makes MK-7 special
MK-7 (menaquinone-7) is the long-chain form of K2 that has become the preferred one in supplements, and the reason is how it behaves in circulation. A short-term human study found that MK-7 levels rose significantly within two to six hours of a single dose and then declined gradually, indicating effective absorption and a sustained presence in the blood (Barna and colleagues, 2024, DOI). That longer circulating time is the practical advantage MK-7 has over shorter-chain forms such as MK-4, which clears more quickly and so needs more frequent dosing.
How vitamin K2 relates to bone and calcium
The reason K2 is paired with vitamin D comes down to its mechanism, which is genuinely elegant. A review describes how vitamin K activates a family of vitamin K-dependent proteins, including osteocalcin, which is involved in building bone matrix, and matrix-Gla protein, which is involved in keeping calcium from accumulating in arterial walls; this activation happens through a process called carboxylation (Karpinski and colleagues, 2017, DOI). In short, K-dependent proteins help direct where calcium goes in the body.
What vitamin K does in the body
Vitamin K earns its place because the body genuinely relies on it: vitamin K contributes to the maintenance of normal bones and to normal blood clotting. Those roles are exactly why K2 is such a logical partner to vitamin D in a bone-focused formula, rather than an afterthought.
Why D3 and K2 are paired
Vitamin D and vitamin K have complementary roles. Vitamin D contributes to the normal absorption and utilisation of calcium and to the maintenance of normal bones, while vitamin K contributes to maintaining normal bones. Combining D3 and K2 brings together two nutrients whose bone-related roles work hand in hand. I explain the pairing in vitamin D3 and K2 for bone health, the question of taking D without K in can vitamin D3 without K2 hurt you, and the wider bone picture in vitamin D and bone health.
How much K2, and is there an upper limit?
Supplements commonly provide around 75 to 100 micrograms of MK-7 a day, which is the amount our formula uses. Vitamin K has a good safety record, and no Tolerable Upper Intake Level has been set for it from food and supplements, because toxicity from natural vitamin K is not generally a concern. That said, more is not automatically better, and the warfarin caution below is the genuinely important limit to respect. I cover dosing alongside D3 in how much D3 and K2 to take daily.
A few cautions worth knowing
- Anticoagulant medicines (warfarin and similar): vitamin K directly affects how these blood-thinning medicines work, so if you take an anticoagulant, do not start a K2 supplement without speaking to your GP or anticoagulant clinic first.
- Pregnancy and breastfeeding: check with your midwife or GP before adding a high-strength D3 and K2 supplement.
- Other medication or a medical condition: have a quick word with your pharmacist if either applies.
Food sources of vitamin K2
Vitamin K2 is found in fermented foods and some animal products. The richest source by far is natto (fermented soybeans), with smaller amounts in certain cheeses, egg yolk and liver. K1, the clotting-associated form, comes mainly from leafy green vegetables. Most diets supply more K1 than K2, which is part of why MK-7 is popular as a supplement.
How our D3 plus K2 is formulated
Our Vitamin D3 + K2 uses vitamin K2 in the MK-7 form, chosen for its favourable absorption profile, alongside 4000 IU of D3 and 100 micrograms of MK-7. It is formulated in the UK and manufactured in a GMP-certified facility. I also compare the 4000 IU question in D3 versus D3 plus K2, and you can browse the full range on the Pure Vitamins UK home page.
Frequently asked questions
What is vitamin K2 MK-7?
MK-7 (menaquinone-7) is a long-chain form of vitamin K2. It is well absorbed and stays in circulation longer than shorter-chain forms, which is why it is the preferred K2 form in supplements.
Is MK-7 better than MK-4?
They are both K2 forms. MK-7 has a longer circulating time, so it is more convenient for once-daily dosing, whereas MK-4 clears faster. That practical difference is why MK-7 is usually chosen for supplements.
Why is K2 combined with vitamin D3?
Because the two have complementary roles in bone health: vitamin D contributes to normal calcium absorption and to maintaining normal bones, and vitamin K contributes to maintaining normal bones.
Can I take K2 if I am on warfarin?
Not without medical advice. Vitamin K directly affects how anticoagulants such as warfarin work, so speak to your GP or anticoagulant clinic before taking any K2 supplement.
This article is for general information, not medical advice. Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. If you are pregnant, breastfeeding, taking medication (including anticoagulants such as warfarin) or managing a medical condition, speak to your GP or pharmacist before starting a new supplement. Signed, Dr. Miron, Founder of Pure Vitamins UK.
