MK-4 and MK-7 are both forms of vitamin K2, but they differ in where they come from, how long they last in your body, and how much you need to take. The short version: MK-7 stays in your bloodstream much longer and works at far lower doses, while MK-4 is cleared quickly and requires dramatically higher amounts to produce similar effects. Both activate the same vitamin K-dependent proteins, but their practical differences matter when choosing a supplement or evaluating your diet.
What MK-4 and MK-7 Actually Are
Both MK-4 and MK-7 belong to a family called menaquinones, which are different forms of vitamin K2. They share the same core ring structure but differ in the length of a molecular “tail” attached to it. MK-4 has a short tail made of 4 repeating units, while MK-7 has a longer tail with 7 units. That tail length is what drives nearly every practical difference between the two, from how they’re absorbed to how quickly your body breaks them down.
Your body can actually convert vitamin K1 (the form found in leafy greens) into MK-4 in certain tissues, which makes MK-4 somewhat unique among the menaquinones. MK-7, on the other hand, is not produced by the body and must come from food or supplements.
Food Sources
MK-4 comes primarily from animal products: eggs, meat, and liver. The amounts in these foods are relatively modest, and you’d need to eat significant quantities to reach the doses used in clinical research.
MK-7 is found in fermented foods like cheese, curd, and sauerkraut. The standout source is natto, a Japanese fermented soybean dish that contains roughly 1,000 micrograms of MK-7 per 100 grams. That’s an exceptionally high concentration, and it’s no coincidence that much of the early vitamin K2 research comes from Japan, where natto is a dietary staple. If you don’t eat natto (and many people outside Japan find its slimy texture unappealing), supplements are the most reliable way to get meaningful amounts of MK-7.
How Long They Stay in Your Body
This is the most important practical difference. MK-4 has a very short half-life in humans. After you take it, blood levels rise and then drop back to baseline within hours. That means a single daily dose doesn’t maintain steady levels throughout the day, and your body clears it before it can do sustained work in tissues outside the liver.
MK-7, with its longer molecular tail, behaves differently. It’s more fat-soluble, circulates longer in the bloodstream, and builds up to stable levels over days of consistent supplementation. This longer half-life is the main reason MK-7 has become the preferred form in cardiovascular research. It reaches tissues like blood vessel walls more effectively because it has more time to get there.
Dosage: Milligrams vs. Micrograms
The dosage gap between MK-4 and MK-7 is striking and often surprises people comparing supplement labels for the first time. Because MK-4 is poorly absorbed and cleared so quickly, clinical trials have used massive doses, typically 45 milligrams per day (that’s 45,000 micrograms), split into three daily doses. This is the pharmacological dose used in Japanese osteoporosis research. Even at lower amounts, studies show you need 600 to 1,500 micrograms per day of MK-4 just to activate the vitamin K-dependent proteins involved in bone metabolism.
MK-7 works at a fraction of those amounts. A dose of 180 micrograms per day has been shown to slow bone loss and maintain bone strength in healthy postmenopausal women. For cardiovascular benefits, trials have used 360 micrograms daily, which effectively reduced levels of a protein marker linked to arterial calcification. In other words, MK-7 achieves measurable effects at roughly 1/250th the dose of MK-4, because so much more of it actually reaches and stays in circulation.
Bone Health
Both forms have been studied for their effects on bone, but the results paint different pictures. In a three-year clinical study, postmenopausal women taking the standard pharmacological dose of MK-4 (45 mg/day) saw no improvement in bone mineral density. They did show improvements in bone quality indices of the femur, suggesting MK-4 may influence how well-structured bone tissue is rather than how dense it appears on a scan.
MK-7 at just 180 micrograms per day inhibited bone loss and helped maintain bone strength in healthy postmenopausal women. The practical takeaway: MK-7 appears to protect against bone loss at a convenient, once-daily dose that’s easy to get from a standard supplement capsule. MK-4 requires a much larger commitment in terms of both pill size and dosing frequency.
Cardiovascular Effects
MK-7 has attracted the most research attention for heart and artery health. It activates a protein in blood vessel walls that helps prevent calcium from being deposited in arteries. When that protein doesn’t get enough vitamin K, it stays in an inactive form and can’t do its job, which contributes to arterial stiffness over time.
Supplementation with MK-7 produces a dose-dependent decrease in the inactive form of this protein, and studies have found improvements in arterial stiffness and the elastic properties of the carotid artery. The longer half-life and better distribution to tissues outside the liver are the main reasons MK-7 is chosen over MK-4 for cardiovascular research. It simply reaches blood vessel walls in higher concentrations.
Where Each Form Ends Up in the Body
MK-4 has a unique trait: your body converts other forms of vitamin K into MK-4 and concentrates it in specific tissues, including the brain, pancreas, and kidneys. This local conversion happens regardless of dietary intake, suggesting MK-4 plays tissue-specific roles that MK-7 doesn’t directly fill. Some researchers believe MK-4 has functions beyond the classic vitamin K role of activating clotting and calcium-regulating proteins, though this area is still being explored.
MK-7, because it stays in the blood longer, is better at reaching the liver (where clotting factors are made) and peripheral tissues like artery walls and bone. If your goal is raising overall vitamin K2 status across the body, MK-7 is the more efficient choice.
Blood Thinners and Safety
If you take warfarin or another vitamin K antagonist, both MK-4 and MK-7 can interfere with the medication’s effectiveness, and this is an area where caution matters. Vitamin K in any form works against these drugs by reactivating the clotting factors they’re designed to suppress.
Because MK-7 is so potent at low doses and accumulates in the body over time, even supplement-level amounts (100 to 200 micrograms) can shift your clotting balance if you’re on warfarin. MK-4 at typical supplement doses (around 100 to 500 micrograms) is less likely to cause problems simply because so little of it stays in circulation, but the pharmacological 45 mg dose used in osteoporosis treatment would certainly interfere. The key consideration for anyone on blood thinners is that any consistent change in vitamin K2 intake, from either form, can affect how well the medication works.
Which One to Choose
For most people comparing supplements, MK-7 is the more practical option. It requires a single small daily dose (typically 100 to 200 micrograms for general health), maintains steady blood levels, and has the strongest clinical evidence for both bone and cardiovascular protection. Most vitamin K2 supplements on the market use MK-7, often derived from natto fermentation.
MK-4 supplements exist, and some products combine both forms. The case for MK-4 rests mainly on its unique tissue accumulation, particularly in the brain, and the Japanese clinical tradition of using high-dose MK-4 for osteoporosis. But at the doses where MK-4 shows benefits (often tens of milligrams), the cost and inconvenience of multiple daily doses make it a harder sell compared to a single MK-7 capsule.
Some people take both, reasoning that MK-4 covers tissue-specific needs while MK-7 handles systemic vitamin K2 status. There’s no evidence this combination is harmful, but there’s also no clinical trial directly comparing the two approaches head to head.