Nutrition Diet: Who Should Not Take Vitamin K3?

October 10, 2025 •

4 min read

Overwhelming scientific evidence from research conducted since the 1980s and 1990s confirms that the synthetic form of vitamin K, known as vitamin K3 or menadione, is toxic and harmful to humans. This crucial information is why the question of Who should not take vitamin K3? has such a clear and definitive answer: everyone should avoid it.

Quick Summary

Vitamin K3 (menadione) is a toxic, synthetic form of vitamin K that is unsafe for human consumption and has been banned for over-the-counter sale in the United States. Its use can cause serious health complications, including liver damage and hemolytic anemia. The safe, natural forms—vitamin K1 and K2—are widely available and should be obtained from food sources.

Key Points

All Humans Should Avoid Vitamin K3: The synthetic form, menadione, is toxic and not safe for human consumption.
Vitamin K3 is Banned for Human Supplements: Due to its toxicity, menadione is not legally sold for human dietary supplementation in the U.S. and other regions.
High-Risk Groups Face Severe Effects: Individuals with G6PD deficiency and infants are especially vulnerable to the dangers of vitamin K3, including hemolytic anemia.
Natural Forms are Safe: Focus on getting Vitamin K1 (from leafy greens) and Vitamin K2 (from fermented foods and animal products), which are natural, non-toxic alternatives.
Dietary Sources are Key: A balanced diet with green leafy vegetables and fermented foods typically provides sufficient vitamin K without the need for unsafe synthetic supplements.
Always Consult a Professional: Before making any decisions about supplementation, it is crucial to consult with a healthcare provider.

The Dangers of Synthetic Vitamin K3 (Menadione)

Unlike the natural forms of vitamin K (K1 and K2), vitamin K3 (also known as menadione) is a synthetic, artificially produced compound that does not occur naturally in foods. Early medical use of menadione was discontinued decades ago due to its toxic effects on the human body. Ingestion of this substance has been linked to severe health issues, which led to its ban from over-the-counter sales in the United States.

Research has shown that vitamin K3 can be toxic to liver cells and lead to the destruction of oxygen-carrying red blood cells, a condition known as hemolytic anemia. This damage is a primary reason for the overwhelming medical consensus that menadione is not a suitable nutritional supplement for humans. Furthermore, in vulnerable populations, the consequences can be even more severe. While often used safely in regulated amounts in animal feed for livestock, its toxicity in humans is well-established.

Specific groups at higher risk

While all humans should avoid vitamin K3, certain individuals face an even higher risk of severe complications from exposure:

Infants and Neonates: Infants, especially premature babies, are particularly sensitive to vitamin K3 toxicity. In the past, the use of menadione was associated with severe health problems in neonates, including jaundice, hyperbilirubinemia, and kernicterus. Today, newborns are typically given a safe form of vitamin K1 to prevent bleeding disorders, a practice that highlights the risks posed by the synthetic version.
Individuals with Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency: This genetic condition affects the body's ability to protect red blood cells from oxidative damage. The strong oxidant properties of vitamin K3 mean that individuals with G6PD deficiency are at a significantly increased risk of developing hemolytic anemia if exposed to menadione.

Safe Alternatives: Natural Vitamin K1 and K2

Fortunately, there is no need to expose oneself to the risks of vitamin K3, as the natural forms of the vitamin are widely available and safe. Vitamin K is a family of compounds, and the two primary forms are K1 (phylloquinone) and K2 (menaquinone). These are the forms found naturally in a healthy diet and the only types approved for human consumption.

Vitamin K1 vs. Vitamin K2

Vitamin K1 (Phylloquinone): This form is primarily found in green leafy vegetables and certain plant oils. It plays a crucial role in blood clotting and is well-absorbed by the body, especially when consumed with a small amount of fat. Excellent food sources include kale, spinach, broccoli, and turnip greens.
Vitamin K2 (Menaquinone): Produced by bacteria in the gut and also found in fermented foods and animal products, vitamin K2 is important for bone health and preventing arterial calcification. Dietary sources include natto (fermented soybeans), sauerkraut, certain cheeses, and some poultry and pork products.

Food sources of natural vitamin K:

Green Leafy Vegetables (K1): Kale, spinach, collard greens, broccoli, Brussels sprouts, turnip greens, and parsley.
Fermented Foods (K2): Natto and some types of cheese.
Animal Products (K2): Egg yolks and certain meats.
Plant Oils (K1): Soybean and canola oil.

Vitamin K3 (Menadione) vs. Natural Vitamin K1 and K2: A Comparison


Feature	Vitamin K3 (Menadione)	Natural Vitamin K1 (Phylloquinone) & K2 (Menaquinone)
Source	Synthetic (artificially produced)	Naturally occurring in plants (K1) and fermented foods/animal products (K2)
Safety for Humans	Toxic; poses a high risk for liver damage and hemolytic anemia	Safe and essential for human health
Human Use	Banned for sale in dietary supplements for humans in many countries, including the U.S.	Readily available and used in human dietary supplements and prescriptions
Side Effects	Allergic reactions, liver toxicity, jaundice, and hemolytic anemia	Very low toxicity potential, allergic reactions are rare
Use in Commerce	Used in regulated amounts for animal feed	Widely sold as safe and effective human supplements

Conclusion: Prioritize Natural Sources for a Healthy Nutrition Diet

In summary, the question of who should not take vitamin K3? has a universal answer: all individuals should avoid it completely. Its documented toxicity makes it unfit for human consumption, a fact recognized by regulatory bans on its use in dietary supplements in many countries. The health risks, which include liver damage and hemolytic anemia, are particularly elevated for infants and those with G6PD deficiency. For a healthy and complete nutrition diet, focus on incorporating the natural and safe forms of vitamin K, K1 and K2, from a variety of foods. These can be easily obtained through a balanced intake of green leafy vegetables and fermented foods, making risky supplementation with synthetic forms completely unnecessary. Always consult a healthcare provider for any concerns about nutritional deficiencies or before starting any new supplement regimen.

Resources

For additional information regarding Vitamin K, refer to the National Institutes of Health (NIH) Office of Dietary Supplements.

Frequently Asked Questions

No, vitamin K3 (menadione) is not safe for human consumption. It is a synthetic form of vitamin K with known toxicity that can cause severe side effects, including liver damage and the destruction of red blood cells.

Vitamin K3 was banned for human use because research showed it caused liver damage and hemolytic anemia. It is no longer sold over-the-counter as a human dietary supplement due to these safety concerns.

Vitamin K1 and K2 are natural forms found in foods like leafy greens and fermented products, respectively, and are safe for humans. Vitamin K3 is a synthetic, toxic form that is not used in human supplements.

While all humans should avoid it, infants and individuals with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency are at a particularly high risk for severe reactions, such as jaundice and hemolytic anemia, from vitamin K3 exposure.

Safe sources of vitamin K include a variety of foods. Vitamin K1 is found in green leafy vegetables, while vitamin K2 is in fermented foods like natto, some cheeses, and certain animal products.

Yes, most people can get adequate amounts of vitamin K from a balanced diet rich in leafy greens and other healthy foods. Vitamin K deficiency is relatively rare in healthy adults.

If you suspect a vitamin K deficiency, consult a healthcare provider. They can determine the appropriate course of action, which will involve safe, natural forms of vitamin K, rather than the dangerous synthetic K3.