MK-4 and MK-7 are two different forms of vitamin K2 (menaquinone). MK-4 has four isoprene units in its side chain, while MK-7 has seven. The half-life of MK-4 in the blood is approximately 1–2 hours, while that of MK-7 is approximately 3 days. On a vitamin K2 label, the form name, amount in micrograms (µg), serving size, %DV, and all-trans ratio are checked.
How do MK-4 and MK-7 differ chemically?
The main difference between MK-4 and MK-7 is the number of isoprene units in the molecule's side chain. Vitamin K2 is not a single molecule but a family of molecules called menaquinones, and the number following the abbreviation 'MK' indicates the number of these units. MK-4 has four isoprene units, while MK-7 has seven; both forms have the same naphthoquinone ring.
Chain length determines the molecule's fat solubility and how it is transported in the body. The longer-chained MK-7 remains in the bloodstream for longer, bound to lipoproteins. Vitamin K1 (phylloquinone) is a separate form with a different side chain. In products where the label states only 'vitamin K' without specifying the form, it cannot be determined whether the content is K1 or K2.
At this point, a frequently asked question is whether forms such as MK-8 or MK-9 also exist. These forms do exist and are found particularly in aged cheeses. However, in the supplement market, the forms that are standard, measurable, and stated on labels are almost exclusively MK-4 and MK-7.
What does the difference in half-life mean in practice?
The half-life of MK-4 in the blood is approximately 1–2 hours, while that of MK-7 is approximately 68–72 hours, or about 3 days. This difference explains why the two forms are used in supplements in very different amounts and at different frequencies.
Because MK-4 is cleared from circulation quickly, it has generally been used in studies in divided doses throughout the day and in milligram amounts; in some Japanese studies, the daily amount reaches 45 mg and is divided into three doses. MK-7, due to its long half-life, is used once a day in microgram amounts. With regular intake, MK-7 levels in the blood stabilize at a more balanced level within a few days.
The difference in units also needs to be considered: 1 mg equals 1000 µg. Someone who sees 100 µg of MK-7 and 1.5 mg of MK-4 on a label may be misled if they compare the two numbers directly, because the half-lives and dosing schedules of the two forms differ. Comparisons between forms should be made not only based on the amount but also by considering the form and frequency of use together.
Where are MK-4 and MK-7 obtained?
The main known dietary source of MK-7 is natto, a Japanese dish fermented with Bacillus subtilis natto bacteria; 100 g of natto contains approximately 900–1000 µg of MK-7. MK-7 in supplements is obtained either from this fermentation process or through chemical synthesis.
MK-4, on the other hand, is found in small amounts in animal-based foods, such as egg yolks and chicken meat; it is around 15–30 µg per 100 g of egg yolk. MK-4 in supplements is largely synthetically produced because extracting it from natural sources on a commercial scale is inefficient.
| Feature | MK-4 (menaquinone-4) | MK-7 (menaquinone-7) |
| Side chain | 4 isoprene units | 7 isoprene units |
| Half-life in the blood | Approximately 1–2 hours | Approximately 68–72 hours |
| Typical amount in supplements | 100 µg–1.5 mg; up to 45 mg in studies | 45–200 µg |
| Frequency of use | Mostly divided doses | Once daily |
| Commercial source | Mostly synthesis | Fermentation (natto) or synthesis |
| Food example | Egg yolk, chicken meat | Natto |
The difference between synthetic and fermentation-derived MK-7 is related more to purity and isomer ratio than to the source itself. This topic is explained in detail in the all-trans section below.
How to read a vitamin K2 label
There are five key pieces of information to check on a vitamin K2 label: the form name, the amount of active ingredient, the unit, the %DV, and the isomer ratio. If this information is not provided together, the product's content cannot be fully evaluated.
Where are the form and amount stated?
Look for a clear statement such as 'vitamin K2 (menaquinone-7)' or 'vitamin K2 (MK-4)' in the nutrient table. If it only says 'vitamin K', the form is unclear. The amount is given per serving in µg (sometimes mcg); it should also be checked whether the serving is 1 capsule or 2 capsules.
Why is the amount of raw material different from the active amount?
MK-7 raw material usually comes as a powder or diluted in oil; a common concentration is 1500 ppm, or 0.15%. In this case, approximately 66.7 mg of raw material is required for 100 µg of active MK-7. Stating '66.7 mg of vitamin K2 powder' in the ingredients list does not mean that there are 66.7 mg of vitamin K2 in the capsule; the value to be used as a basis is the µg amount in the nutrient table.
How is the %DV calculated?
In Turkey, the Dietary Reference Value (DRV) for vitamin K is 75 µg. Accordingly, 75 µg is written as 100%, 100 µg as approximately 133%, and 200 µg as approximately 267%. The same calculation logic applies to other vitamins in multi-component products; detailed examples are available in the label reading guide on how to read multivitamin content.
Label checklist:
- Is the form name clearly stated (MK-4 or MK-7)?
- Is the amount given in µg per serving?
- How many capsules or tablets make up a serving?
- Is the %DV consistent with the 75 µg reference?
- Is the all-trans ratio stated?
Why are the all-trans and cis forms stated on the label?
The MK-7 molecule can exist as an all-trans or cis isomer depending on the spatial arrangement of the double bonds in the side chain. The form that occurs naturally in foods and is referenced in scientific literature is the all-trans form; cis isomers have a different structure and are not evaluated in the same way. Therefore, in high-quality raw materials, the all-trans ratio is generally stated as 98% or higher.
The cis isomer ratio may increase under uncontrolled synthesis conditions. In addition, contact with light and certain mineral salts, such as calcium or magnesium carbonate, can lead to the degradation of MK-7 throughout its shelf life. This is why some manufacturers use microencapsulated raw material and offer the product in light-resistant packaging.
If the all-trans ratio is not on the label, a certificate of analysis (CoA) can be requested from the manufacturer. The certificate includes the MK-7 amount and isomer ratio measured using the HPLC method. Regardless of whether the source is fermentation or synthesis, these measurable values are what matter.
What common pieces of information are incorrect?
A significant portion of the information circulating about vitamin K2 stems from confusion about the form, unit, and raw material. The following five statements are frequently repeated but are not correct:
- 'K1 and K2 are the same': K1 and K2 are separate forms with different side chains and different dietary sources; K1 is found mainly in green leafy vegetables.
- 'MK-7 is superior to MK-4 in all cases': The two forms have different half-lives and dosing schedules; declaring one form generally superior is not a measurable comparison.
- 'A higher µg amount is better': The common range for MK-7 in supplements is 45–200 µg, and the recommended daily serving on the label should not be exceeded.
- 'Naturally sourced MK-7 is a different molecule from synthetic': Both sources yield the same molecule in the all-trans form; the difference lies in purity and isomer ratio.
- 'The mg value in the ingredients list is the vitamin amount': The list generally shows the weight of the diluted raw material; the active amount is stated in the nutrient table.
Who is it suitable for, and who should be careful?
Vitamin K2 supplements are products intended for adults who wish to use them according to the serving size on the label. For those following a vegan diet, MK-7 from fermentation is plant-based; however, it should also be checked whether the capsule shell is gelatin or plant-based cellulose (HPMC).
Those taking anticoagulant medications in the vitamin K antagonist group (such as warfarin) should consult the physician who prescribed the medication before starting any supplement containing vitamin K, because changes in vitamin K intake can affect the regulation of these medications. The standard warning on the label also applies to pregnant and breastfeeding women and those taking regular medication. If the product is not intended for children, the age limit stated on the label should be followed.
For those using multiple products, the total amount is important. When a multivitamin containing K2 is used together with a separate K2 product, the daily amount can unknowingly double; therefore, the µg values on all labels should be added together. To find the vitamin K line and serving size definition on a multivitamin label, the steps in the label reading guide can be followed.
What practical steps are followed when choosing a K2 product?
Practical evaluation begins on the back of the label. First, the form name and µg amount are read, followed by the serving size definition, and finally the all-trans ratio and raw material source.
1. Find the MK-4 or MK-7 statement in the nutrient table.
2. Note the µg amount per serving and compare it with the 75 µg DRV.
3. Do not confuse the raw material weight in the ingredients list with the active amount.
4. Check the all-trans ratio (98% or higher) or the certificate of analysis.
5. Taking into account that vitamin K2 is fat-soluble, use the product with a meal containing fat.
6. Store the packaging away from light and below 25 °C.
These six steps allow K2 products from different brands to be compared using the same criteria. Once the form, amount, and isomer ratio are clear, the numbers on the label can be read not in isolation, but in relation to each other.
Frequently asked questions
What is the main difference between MK-4 and MK-7?
Both forms belong to the vitamin K2 (menaquinone) family. MK-4 has four isoprene units in its side chain, while MK-7 has seven. The half-life of MK-4 in the blood is approximately 1–2 hours, while that of MK-7 is approximately 3 days.
What does it mean if the label states only 'vitamin K'?
In this case, it cannot be determined whether the content is K1 or K2, or if it is K2, which form it is. A clear form name such as MK-4 or MK-7 should be looked for in the nutrient table.
Why is the mg value in the ingredients list different from the value in the nutrient table?
MK-7 raw material is mostly used as diluted powder or oil. The ingredients list shows the weight of this raw material; the active vitamin K2 amount is stated in µg in the nutrient table.
How is the %DV calculated for vitamin K?
In Turkey, the Dietary Reference Value for vitamin K is 75 µg. The %DV is found by dividing the µg amount per serving by 75 and multiplying by 100; for example, 100 µg is approximately 133%.
Why is the all-trans ratio important?
The MK-7 form that occurs naturally in foods and is referenced in literature is the all-trans form. To evaluate raw material quality, the all-trans ratio is expected to be stated on the label or certificate of analysis; this ratio is generally 98% or higher.
