What Is the MK-4 Form of Vitamin K2 and How Does It Differ From MK-7?
MK-4 is a form of vitamin K2 found in small amounts in meat, eggs and dairy, and your body also makes it from the vitamin K1 in leafy greens. As a pill, MK-4 behaves very differently from MK-7: at small, food-like doses it barely shows up in the blood, while MK-7 builds up there. MK-4 does its best-tested work at a much higher dose, 45 mg a day, which is an osteoporosis drug in Japan.
Vitamin K comes in two main families. Vitamin K1 (phylloquinone) comes from plants. Vitamin K2 is a group of related molecules called menaquinones, shortened to MK. The number after “MK” tells you how long the molecule’s tail is. MK-4 has a short tail. MK-7 has a long one, and that difference changes how each one moves through your body.
All forms of vitamin K do the same core job. They switch on proteins that need vitamin K to work: clotting factors made in the liver, and proteins such as osteocalcin in bone and matrix Gla protein in blood vessel walls. When there is not enough vitamin K, osteocalcin stays in an inactive form called undercarboxylated osteocalcin, which researchers use as a marker of low vitamin K in bone.
What the Data Show
The page’s original study is a head-to-head absorption study in healthy Japanese women. Each woman took a single 420 μg dose of either MK-4 or MK-7 with breakfast. MK-7 was well absorbed, peaked in the blood 6 hours later, and could still be measured 48 hours after the dose. MK-4 was not detectable in the blood of any woman at any time point.
In the second part of the study, the women took 60 μg a day of one form for 7 days. That dose matches what people get from diet. MK-7 raised blood MK-7 levels significantly in every woman. MK-4 did not raise blood MK-4 levels at all.
A separate study in healthy volunteers explains why MK-7 behaves this way. It compared MK-7 with vitamin K1. Both were absorbed well, but MK-7 has a very long half-life (the time it takes for half of it to clear the blood). With daily use, MK-7 built up to levels 7 to 8 times higher than K1, and it switched on more osteocalcin.
Two cautions apply. The head-to-head study was small and was run partly by an MK-7 maker. And MK-4 lives mainly inside tissues, so blood levels are not the whole story.
Where Does MK-4 Come From?
There are two sources: food and your own cells.
Food. MK-4 is found in animal foods. A US analysis of meat, dairy, eggs and fast food measured three forms of vitamin K, including MK-4, across hundreds of samples. No single food in those groups turned out to be a rich source of any one form. They matter because people eat a lot of them.
Your own tissues. MK-4 is found in tissues outside the liver throughout the body, with particularly high amounts in the brain, kidney and pancreas of humans and rats. Researchers had long shown that the body converts vitamin K1 into MK-4. In 2010, a study in Nature identified the human enzyme that does it, called UBIAD1. That enzyme kept working even in the presence of warfarin, the blood thinner that blocks vitamin K recycling.
How does K1 get turned into MK-4? A tracer study in rats followed labeled vitamin K1 through the body. The gut breaks part of the K1 down to menadione (vitamin K3), which travels in the blood to tissues. The tissues then rebuild it into MK-4. The authors called menadione a major source of tissue MK-4. This full pathway has been shown in animals, not traced step by step in people.
MK-4 vs MK-7: Which Is Better?
It depends on what you want the supplement to do, and on the dose.
| MK-4 | MK-7 | |
|---|---|---|
| Main food sources | Meat, eggs, dairy (small amounts) | Natto and other fermented foods |
| Made by your body? | Yes, from vitamin K1 | No |
| Small doses (micrograms) raise blood levels? | No, in the one head-to-head study | Yes, and it builds up over days |
| Dose used in bone trials | 1.5 mg to 45 mg a day | 100 to 180 μg a day |
| Best-tested use | 45 mg a day for osteoporosis in Japan | Low daily doses for bone markers and bone loss |
For raising vitamin K levels at small doses, MK-7 wins. It is absorbed, it lasts, and it builds up. In a dose-finding trial in Japanese adults, 100 μg or more of MK-7 a day was enough to improve the activation of osteocalcin. That trial was also run by an MK-7 maker.
MK-4 needs far larger doses. The studies that show effects from MK-4 use milligrams, not micrograms. One milligram is 1,000 micrograms, so even the low-dose MK-4 trial below used 25 times the daily amount that did nothing to blood levels in the head-to-head study.
No trial has compared MK-4 and MK-7 directly on bone density or fractures. Any claim that one is better for your bones goes beyond the evidence.
Is MK-4 Good for Your Bones?
This is where most of the MK-4 research sits. MK-4 given at 45 mg a day has been used to treat osteoporosis in Japan, under the drug name menatetrenone.
The early results looked dramatic. A 2006 meta-analysis pooled 7 trials that reported fractures. All 7 were Japanese and all used MK-4. Compared with controls, the odds of a spine fracture were about 60% lower, the odds of a hip fracture about 77% lower, and the odds of any fracture outside the spine about 81% lower.
Those numbers did not hold up. An updated 2019 review of 36 trials noted that the integrity of some of the earlier evidence had been questioned since the previous review was published. Across all forms of vitamin K in postmenopausal or osteoporotic patients, it found about 28% lower odds of any clinical fracture, which shrank and lost statistical significance when only trials at low risk of bias were counted. There was no difference in spine fractures. The authors concluded that vitamin K may reduce clinical fractures, but the evidence is not strong enough to confirm it.
A 2019 meta-analysis limited to MK-4 looked at 18 trials with 8,882 patients. MK-4 raised spine bone density slightly compared with placebo, by 0.05 g/cm². Its effect on spine fractures was not statistically significant, and the authors called the fracture benefit uncertain.
The largest Western trial points to bone shape rather than density. In a 3-year randomized trial of 325 Dutch postmenopausal women, 45 mg of MK-4 a day did not change bone density on a standard scan. It did increase bone mineral content and the width of the hip bone’s neck. Hip bone strength held steady in the MK-4 group, while it fell significantly in the placebo group.
Do Low-Dose MK-4 Supplements Work?
Most MK-4 supplements on shelves are not 45 mg. Some are close to 1.5 mg, and one trial tested that dose.
In a 12-month double-blind trial of 48 postmenopausal Japanese women, half took 1.5 mg of MK-4 a day and half took a placebo. At 6 and 12 months, the MK-4 group had significantly lower levels of inactive osteocalcin. Forearm bone density fell in the placebo group between 6 and 12 months, while it did not drop significantly in the MK-4 group. The researchers reported no substantial side effects.
That is one small trial using a forearm measurement, with no fracture data. For comparison, MK-7 has a larger long-term trial: in 244 healthy postmenopausal women given 180 μg of MK-7 a day for 3 years, MK-7 slowed the age-related loss of bone density at the spine and the hip’s femoral neck, though not at the total hip, and it helped preserve bone strength.
Is MK-4 Safe? Side Effects to Know
At low doses, MK-4 looked safe in the 1.5 mg trial above. At the 45 mg drug dose, the MK-4 meta-analysis found adverse events were about 47% more common than with placebo, and adverse drug reactions about 29% more common. Serious adverse events were not more common.
The bigger safety question is blood thinners. Vitamin K is what warfarin works against, so any vitamin K supplement can change how warfarin works. I cover that in detail in Even Low-Dose Vitamin K2 Can Disrupt Blood Thinners. If you take warfarin, do not start or stop any form of vitamin K without talking to the doctor who manages it.
Dr. Kumar’s Take
MK-4 is not a lesser vitamin. It is the form your own tissues build and store, and the enzyme that makes it was only identified in 2010. What the evidence says is narrower: swallowing a small MK-4 capsule does not do much to the vitamin K in your blood, while the same small dose of MK-7 does.
The bone story deserves an honest reading. The big fracture numbers from the early Japanese trials shrank once questionable data were set aside, and what remains is a modest, uncertain benefit. If you want a K2 supplement for general vitamin K status, the microgram-dose evidence favors MK-7. MK-4 makes sense mainly at milligram doses, and that is a decision about bone treatment, not a daily vitamin.
Practical Takeaways
- MK-4 is vitamin K2 from meat, eggs and dairy, and your body also makes it from vitamin K1 in leafy greens.
- At microgram doses, MK-7 raises blood vitamin K levels; MK-4 does not.
- If you buy MK-4, check the dose. The trials that found effects used 1.5 mg to 45 mg a day, not micrograms.
- Do not expect a fracture guarantee from either form. The fracture evidence is uncertain.
- On warfarin, change nothing about vitamin K supplements without your prescriber.
Related Studies and Research
- Vitamin D3 and K2 Together Raise Spine Bone Density in Older Women
- Do Natto Eaters Have More Vitamin K2 and Denser Bones?
- Can Vitamin K2 (MK-7) Improve Bone Strength Without Raising Bone Density?
- 3-Year Study Finds Vitamin K2 (MK-7) Helps Prevent Bone Loss in Postmenopausal Women
- Even Low-Dose Vitamin K2 Can Disrupt Blood Thinners
FAQs
What is MK-4 vitamin?
MK-4 (menaquinone-4) is one form of vitamin K2. It is found in meat, eggs and dairy, and your tissues make it from vitamin K1. As a drug, it is called menatetrenone and is used for osteoporosis in Japan at 45 mg a day.
Is MK-4 or MK-7 better?
At small doses, MK-7 is better at raising vitamin K in the blood, because it is absorbed well and lasts for days. MK-4 needs milligram doses to show effects in trials. No study has compared the two directly on bone fractures.
Can your body convert vitamin K1 to MK-4?
Yes. An enzyme called UBIAD1 makes MK-4 in human cells. Animal studies show the gut breaks vitamin K1 down to menadione, which tissues then rebuild into MK-4.
What foods are high in MK-4?
Meat, eggs and dairy contain MK-4, but a US analysis found no single food in those groups is a rich source. They add up because people eat them often. Natto, a fermented soybean food, is the richest food source of MK-7, not MK-4.
Is it safe to take MK-4 every day?
A daily 1.5 mg dose for a year caused no substantial side effects in one trial. At the 45 mg drug dose, side effects were more common than with placebo, though serious ones were not. Anyone on warfarin should talk to their prescriber before taking any form of vitamin K.
Bottom Line
MK-4 is the form of vitamin K2 your tissues make and store, fed partly by the vitamin K1 in leafy greens. As a supplement, it does little to blood vitamin K levels at microgram doses, while MK-7 does. MK-4’s best-tested use is the 45 mg osteoporosis dose, where it raised spine bone density slightly but has an uncertain effect on fractures.
