The abbreviation “MK” in the name of vitamin K2 is not accidental: the number after it tells you how many isoprene units make up the side chain of the molecule. In Zielona Góra we ferment soya with the bacterium Bacillus subtilis natto, which produces menaquinone-7 (MK-7), one of the dozen or so menaquinone forms described in the literature. I have gathered here what is known with certainty about the differences between MK-7 and MK-4: chemical structure, pharmacokinetics, dietary sources, and what health claims about vitamin K are actually permitted in the European Union.
⚠️ Are you taking anticoagulant medication (for example acenocoumarol or warfarin)? Natto and preparations containing vitamin K2, regardless of whether in MK-7 or MK-4 form, may affect how these medicines work. Consult your diet and supplements with a doctor. See the important legal and medical information.
In short
- MK-7 has a longer side chain (seven isoprene units) and stays in the blood longer than MK-4. It forms naturally during bacterial fermentation, and natto is one of the richest known dietary sources.
- MK-4 has a shorter chain (four isoprene units) and stays in the blood for a shorter time. It occurs mainly in animal products, and the body can also convert other forms of vitamin K into it.
- Regardless of the form: vitamin K contributes to normal blood clotting and to the maintenance of normal bones, the only two health claims authorised for vitamin K in the European Union (Regulation (EU) 432/2012). The well-documented pharmacokinetic differences between MK-7 and MK-4 do not change the scope of these claims.
Menaquinones, the other face of vitamin K
Vitamin K is not a single compound but a family of related molecules. Phylloquinone, or vitamin K1, occurs mainly in green leafy vegetables such as spinach or kale. Menaquinones, or vitamin K2, differ in the length of the side chain built from isoprene units, hence the designations from MK-4 to MK-13: the number after the MK abbreviation is precisely the number of these units. MK-4 has four of them, MK-7 has seven, which translates into a different molecular size and different physicochemical properties. Both forms take part in the activation of vitamin K-dependent proteins such as osteocalcin, involved in calcium binding in bones, and MGP (matrix Gla protein), a protein analysed in the literature in the context of calcium metabolism. This is a description of the biochemical function of these proteins, not a declaration of a health effect.
MK-7 and MK-4, differences in structure and pharmacokinetics
Both forms fulfil the same basic role in the body as vitamin K, but differ in structure and in how they behave after ingestion.
MK-7
- The long side chain (seven isoprene units) means that MK-7 stays in the blood longer than MK-4: the plasma half-life is measured in hours to tens of hours.
- It shows good bioavailability after oral intake.
- It forms naturally during bacterial fermentation, for example when Bacillus subtilis natto ferments soya. Natto is one of the richest sources of this form described in the literature.
- Thanks to the longer time in the blood, a single daily dose usually suffices in supplementation.
MK-4
- A shorter chain (four isoprene units) and a shorter time in the blood, which is why it is taken more frequently in supplementation.
- It occurs naturally in animal products such as liver, egg yolks and aged cheeses.
- The body can to some extent convert other forms of vitamin K, including K1, into MK-4.
| Property | MK-7 | MK-4 |
|---|---|---|
| Isoprene units in the chain | seven | four |
| Time in the blood | long (hours to tens of hours) | short (a few hours) |
| Origin | natto (fermented soy) | animal products |
| Bioavailability | high | moderate |
| Dosing frequency in supplements | once a day | several times a day |
The comparison shows that MK-7 is more convenient to use because of its longer time in the blood and once-a-day dosing, and the difference in the number of isoprene units in the side chain is the most fundamental chemical difference between the two forms.
Where MK-7 comes from and where MK-4 comes from
MK-7 is a product of bacterial fermentation: in nature it forms mainly where fermentation takes place, and the best-known example is natto, soya fermented with a Bacillus subtilis natto culture. MK-4 comes primarily from animal products, although the body can also synthesise it endogenously from other forms of vitamin K. Fresh natto as a food naturally delivers vitamin K2 in the MK-7 form, without additional processing.
Typical doses of MK-7 in supplements are 100 to 200 µg per day; MK-4 is usually taken in higher doses several times a day, in accordance with the manufacturer’s instructions for the preparation. Vitamin D3 is sometimes combined with K2 in a single product: vitamin D contributes to the normal absorption and utilisation of calcium, this is a separate authorisation relating to vitamin D, independent of the status of vitamin K described above.
Check our fresh natto, a natural source of vitamin K2 in the MK-7 form
Safety and precautions
Natto and preparations containing vitamin K2 are safe for most healthy people. Because of the presence of vitamin K, particular caution is warranted in a few situations.
This applies above all to people taking anticoagulant medicines from the vitamin K antagonist group (for example warfarin or acenocoumarol), because vitamin K can affect how these medicines work regardless of whether it comes from the MK-7 or MK-4 form. Consult your attending doctor about supplementation and a diet rich in vitamin K2. Caution is also advisable during pregnancy and breastfeeding and when taking other medicines regularly. Natto contains soya, so it is not intended for people with a soya allergy. A food supplement does not replace a varied diet and a healthy lifestyle.
Summary
MK-7 and MK-4 are two forms of vitamin K2 that differ in the number of isoprene units in the side chain, dietary sources and time in the blood: MK-7 has seven, stays in the body longer and comes mainly from fermentation, as in natto; MK-4 has four, acts for a shorter time and occurs mainly in animal products. Regardless of the form, vitamin K contributes to normal blood clotting and to the maintenance of normal bones, and the choice of form is above all a matter of dosing convenience.
FAQ. Frequently asked questions about vitamin K2 MK-7 and MK-4
How does MK-7 differ from MK-4?
Both are forms of vitamin K2 (menaquinones), differing in the length of the side chain: MK-7 has seven isoprene units, MK-4 has four. This difference translates into the time both forms spend in the blood and into their dietary sources: MK-7 comes mainly from fermentation, as in natto, MK-4 mainly from animal products.
Why does MK-7 stay in the blood longer than MK-4?
The longer side chain of MK-7 (seven isoprene units versus four in MK-4) is associated with a longer plasma half-life. This is a pharmacokinetic difference, well described in the literature, and not an additional health effect.
Can vitamin K2 be combined with vitamin D3?
Yes, both ingredients are sometimes combined in a single preparation. Vitamin D contributes to the normal absorption and utilisation of calcium, this is a separate authorisation relating to vitamin D, independent of the status of vitamin K described above.
Can everyone take vitamin K2 MK-7?
For most healthy people, yes. The exception is people taking anticoagulant medicines from the vitamin K antagonist group, who should consult their doctor about supplementation.
Where does the vitamin K2 MK-7 in natto.pl products come from?
It comes from the fermentation of soya with a Bacillus subtilis natto culture, a natural process in which this form of vitamin K is produced. Our fresh natto speaks most clearly about it, because it is soya straight after fermentation, without further processing.
Does vitamin K2 have authorised health claims in the European Union?
Yes, but only two, and they relate to vitamin K as such, regardless of the form: vitamin K contributes to normal blood clotting and to the maintenance of normal bones (Regulation (EU) 432/2012). No other claim about the superiority of one form over another in terms of health effect falls within this scope.
Sources
- Regulation (EC) No 1924/2006 on nutrition and health claims made on foods, text on EUR-Lex
- EU Register of Nutrition and Health Claims (EU Register on nutrition and health claims), European Commission
- European Food Safety Authority (EFSA), the European authority evaluating the scientific basis of health claims for food
Legal and medical note. This article is educational and does not replace the advice of a doctor or pharmacist. Vitamin K has two authorised health claims in the European Union (Regulation (EC) 1924/2006, Regulation (EU) 432/2012): it contributes to normal blood clotting and to the maintenance of normal bones. Beyond these two claims, we do not attribute any additional health effect to the MK-7 or MK-4 form, and a food supplement is not a medicine and does not replace a varied diet. Full information is on the Legal and medical information page.
