Vitamin K3: What you really need to know
ca. 11 Minuten
Vitamin K3 comes up repeatedly in searches by people looking to improve their vitamin K intake. The problem is that many don't know this substance is not a natural form of the vitamin. Menadione, the chemical name for vitamin K3, is a completely synthetic compound. It is found in no food, does not perform a vitamin function in the human body, and is banned in the EU as a dietary supplement for humans because of its toxicity. This article explains the facts without causing alarm.
Table of contents
- Key takeaways
- Vitamin K3 compared with K1 and K2
- Health risks of vitamin K3
- Legal status of vitamin K3 in the EU
- Safe alternatives for getting enough vitamin K
- My assessment of vitamin K3
- Your next step toward optimal nutrient intake
- FAQ
Key takeaways
| Item | Details |
|---|---|
| Vitamin K3 is synthetic | Menadione is found in no natural food source and is not a true vitamin for humans. |
| K3 is banned in the EU | Vitamin K3 is not approved in the EU as a dietary supplement for humans and is considered toxic. |
| Natural alternatives exist | Vitamin K1 from leafy greens and K2 from fermented foods safely meet requirements. |
| K2 and vitamin D work together | The combination of vitamin K2 and vitamin D is particularly effective in supporting bones and blood vessels. |
| Detect deficiencies early | A nutrient check can help identify a vitamin K deficiency before symptoms develop. |
Vitamin K3 compared with K1 and K2
The vitamin K family includes three known forms that differ fundamentally. Confusing them can quickly lead to poor decisions when buying supplements.
Vitamin K1 (phylloquinone) is the form found in plants. Spinach, kale, broccoli, and herbs such as parsley are particularly rich sources. In the body, K1 mainly regulates blood clotting. It is fat-soluble and is best absorbed with a meal containing fat.
Vitamin K2 (menaquinone) is produced through fermentation. Bacteria produce it in fermented foods such as natto, sauerkraut, and certain cheeses. K2 activates proteins for bones and blood vessels, making it particularly relevant for long-term health. The MK-7 subtype is considered especially bioavailable.
Vitamin K3 (menadione) is a different story. It is a purely synthetic substance that is not found in foods and does not perform a genuine vitamin function in the body.
| Feature | Vitamin K1 | Vitamin K2 | Vitamin K3 |
|---|---|---|---|
| Origin | Plants | Fermentation, bacteria | Synthetic |
| Solubility | Fat-soluble | Fat-soluble | Water-soluble (historically) |
| Main function | Blood clotting | Bone and vascular health | No natural function |
| Suitable for humans? | Yes | Yes | No |
| EU approval as a supplement | Yes | Yes | No |
Important to understand: The numbering K1, K2, K3 suggests a series of related substances. In reality, K3 is biochemically barely comparable to K1 and K2. It is not a relative, but a misstep from the early history of vitamin research.
Pro tip: Always check the exact designation when buying supplements. “Vitamin K” on a label could mean K1, K2, or a combination. K3 must not be included in human dietary supplements in the EU.
Health risks of vitamin K3
Researchers once believed that the water-soluble form of a vitamin K might offer benefits because it is more easily absorbed than fat-soluble forms. This assumption turned out to be dangerously wrong.
Menadione disrupts glutathione metabolism, damages cell walls, and causes hepatotoxic effects. Specifically, this means the substance interferes with a central protective mechanism in cells. Glutathione is one of the body’s most important antioxidants. When its function is disrupted, cells are left defenseless against oxidative stress.
The liver is particularly affected. Vitamin K3 was completely withdrawn from human medicine because of its severe hepatotoxicity. This is not a minor caveat, but an active ban based on clinical observations.
Risks at a glance:
- Hepatotoxicity: direct damage to liver cells at higher doses
- Oxidative stress caused by inhibition of glutathione synthesis
- Hemolysis: destruction of red blood cells, particularly documented in newborns
- Cell wall damage in various tissues
- No proven therapeutic effect in humans that would justify these risks
“Vitamin K3 is not a therapeutic option for humans. Consumer advocates and nutrition experts emphasize that K3 is primarily used in the animal feed industry and should stay there.” Source: Verbraucherzentrale
For comparison: Vitamins K1 and K2 are considered safe in normal amounts, even when taken over a longer period. K1 has no known toxicity threshold from dietary intake. K2 is well tolerated even at higher supplemental doses. This safety record does not exist for K3.
What many people don’t know is that clinical reports of harm caused by K3 use in newborns date back to the 1980s. This led to the substance being gradually withdrawn from pediatrics and later from human medicine altogether. Today, menadione is approved only for animal feed, where it is used as a precursor for the body’s own K2 synthesis in some animal species.
Pro tip: If you buy a supplement that contains “vitamin K” but doesn’t specify the exact form, ask the manufacturer for the specifications. Reputable products always state whether it is K1, MK-4, or MK-7.
Legal status of vitamin K3 in the EU
EU Directive 2002/46/EC governs which vitamins and minerals are approved for use in dietary supplements for humans. Vitamin K3 (menadione) is not on this list. The EFSA permits health claims only for K1 and K2, not for synthetic K3.
This is no bureaucratic coincidence. The EFSA (European Food Safety Authority) assesses substances for safety and proven benefits. K3 does not pass this assessment because the potential for harm outweighs the possible benefits, and no proven benefits for humans have been documented.
| Substance | Status in EU supplements | EFSA approval | Use |
|---|---|---|---|
| Vitamin K1 | Approved | Yes | Human and animal nutrition |
| Vitamin K2 (MK-4, MK-7) | Approved | Yes | Human and animal nutrition |
| Vitamin K3 (menadione) | Not approved | No | Animal nutrition only |
What this means for you as a consumer: Any product sold as a dietary supplement in the EU that contains vitamin K3 is either mislabeled or violates current law. Anyone who orders such products online from non-EU countries assumes the full health risk themselves.
Nothing has changed in this legal situation in 2026. There is no discussion of loosening the rules, as no new safety data have emerged to justify a reassessment. So anyone hoping K3 supplements might eventually be legalized is waiting for something that cannot be scientifically justified.
Pro tip: Check the ingredients list whenever you buy a supplement for “Menadione” or “Menadionum.” These names are chemical synonyms for vitamin K3 and should not appear in human supplements.
Safe alternatives for getting enough vitamin K
If K3 is not an option, the reasonable question is: How can I safely meet my vitamin K requirements? The answer is encouraging: a balanced diet can meet these requirements very well.
Natural sources of vitamin K1
Vitamin K1 is found mainly in green foods:
- Kale: about 817 µg per 100 g
- Spinach: about 483 µg per 100 g
- Broccoli: about 102 µg per 100 g
- Parsley and chives: especially rich in K1
- Lamb's lettuce, Brussels sprouts, peas
According to the German Nutrition Society, the recommended daily intake for adults is 60 to 80 µg. Eating green vegetables regularly almost automatically provides enough.
Natural sources of vitamin K2
Vitamin K2 is found in fermented foods and certain animal products:
- Natto (Japanese soy product): by far the richest source
- Hard cheeses such as Gouda or Emmental
- Butter and lard from pasture-raised animals
- Chicken liver
- Sauerkraut in small amounts
Here’s an interesting detail about K2: not everyone eats natto every day. Those who don’t reliably get K2 from their diet may benefit from a high-quality supplement. The MK-7 form is considered particularly long-lasting in the bloodstream and is therefore preferred.
How K2 and vitamin D work together
K2 and vitamin D are a particularly effective duo. Vitamin D promotes calcium absorption from the gut. K2 then helps ensure that this calcium is actually incorporated into the bones instead of being deposited in the walls of blood vessels. Anyone who wants to know how to get vitamin D through their diet can find a detailed guide on mybody x.
Anyone who chronically gets little sun and also eats few fermented foods should have their K2 and D3 levels measured rather than guessing. Blind supplementation is rarely the best strategy because individual needs can vary widely.
Pro tip: Always combine K2 supplements with vitamin D3 and a meal containing fat. Both are fat-soluble and are absorbed much better this way.
Anyone who regularly takes blood thinners such as warfarin should consult a doctor about their vitamin K intake. Vitamin K directly affects the clotting cascade and can influence how these medications work. This applies to K1 and K2, not just K3.
The most common nutrient deficiencies in Germany show that true vitamin K deficiency is rare in the general population, but certain at-risk groups, including older adults, people with intestinal disorders, and those on very low-fat diets, may be affected. Finding out early whether you have a deficiency is a wiser choice than waiting for symptoms to appear.
My assessment of vitamin K3
I’m regularly asked whether vitamin K3 might have some benefits that are being overlooked in public discussion. My answer is clear: no.
What concerns me about this topic is not the substance itself, but the pattern behind it. Time and again, health-conscious people look for shortcuts and synthetic options, even though natural alternatives are right in front of them. Leafy greens, fermented cheese, a good MK-7-based K2 supplement. It doesn’t have to be complicated.
I have seen people invest a great deal of time and money in questionable supplements they order online from other countries. The risk they take is not at all proportionate to the supposed benefit. Menadione is clearly categorized by science and regulators. There is no hidden truth that experts are keeping from the public.
My honest advice: Get your vitamin K levels tested before supplementing anything. If you don't know your baseline, you're optimizing blindly. And once you know where you stand, you can act in a targeted and safe way. Natural sources first, targeted supplements when a need has been confirmed, and no synthetic substances for which neither approval nor proof of safety exists.
— MYBODY X
Your next step toward optimal nutrient intake
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FAQ
What is vitamin K3 and why is it dangerous?
Vitamin K3, known chemically as menadione, is a synthetic substance that does not occur naturally in foods. It disrupts glutathione metabolism, damages liver cells, and was therefore withdrawn entirely from human medicine.
Is vitamin K3 legal as a supplement in Germany or the EU?
No. K3 is not approved in the EU as a dietary supplement for humans. The EFSA approves only K1 and K2 for this purpose.
Which foods contain natural vitamin K?
Vitamin K1 is found in kale, spinach, and broccoli. Vitamin K2 is found in fermented foods such as natto and sauerkraut, as well as in hard cheese and butter from pasture-raised cows.
When is a vitamin K supplement useful?
A supplement makes sense if a genuine deficiency has been confirmed or if your diet consistently contains little green vegetables and fermented foods. The MK-7 form is considered particularly bioavailable for K2 supplements.
How do vitamins K2 and D work together?
Vitamin D promotes calcium absorption from the gut, while K2 directs its incorporation into bones and prevents deposits in blood vessels. Taking both together is therefore particularly effective for bone and vascular health.
