How do I get vitamin K3 and why is it unsafe?

December 27, 2025 •

3 min read

According to research from the 1980s and 1990s, vitamin K3 (menadione) has been linked to liver damage and the destruction of red blood cells in humans. The critical truth to understand is that you should not and cannot get vitamin K3 for human consumption, as it is a synthetic and harmful compound. This guide explains why it's off-limits and directs you toward the safe, natural forms of vitamin K your body actually needs.

Quick Summary

Vitamin K3, or menadione, is a toxic, synthetic form of vitamin K that is not available for human consumption due to serious health risks, including liver damage and anemia. The body relies on natural vitamin K1 and K2, found in leafy greens, fermented foods, and some animal products. It's crucial to seek out these safe dietary sources instead of vitamin K3.

Key Points

Synthetic and Unsafe: Vitamin K3, or menadione, is a synthetic compound not meant for human consumption due to its toxicity.
Toxic Effects: Studies show vitamin K3 can cause severe side effects in humans, including liver damage and hemolytic anemia.
Not for Human Supplements: Regulatory bodies have banned vitamin K3 from dietary supplements for humans.
Used in Animal Feed: The synthetic vitamin is used safely in controlled doses in feed for livestock and pets.
Focus on Natural K1 and K2: To get healthy vitamin K, rely on natural food sources containing vitamin K1 (leafy greens) and vitamin K2 (fermented foods, animal products).
Increase K1 Absorption: Eat K1-rich leafy greens with a source of fat, like olive oil, to improve your body's ability to absorb it.
Consult a Doctor: It is essential to consult a healthcare provider regarding vitamin K intake, especially if you take blood-thinning medication.

The Dangerous Reality of Vitamin K3

Many people are unaware that not all vitamins are created equal, and this is especially true for the different forms of vitamin K. While vitamins K1 (phylloquinone) and K2 (menaquinones) are natural, healthy forms found in food, vitamin K3 (menadione) is a synthetic analog. Unlike its natural counterparts, menadione is not derived from natural sources and poses significant health risks to humans, which is why it is banned from over-the-counter sales in the United States and other regions.

Why You Cannot Get Vitamin K3

The quest to acquire vitamin K3 is a misguided one, driven by a lack of awareness about its toxicity. Health authorities and regulatory bodies strictly prohibit its use in human supplements and fortified foods for several critical reasons:

Significant Health Risks: Studies from the 1980s and 1990s revealed menadione's harmful effects on humans, which include liver toxicity, jaundice, and the destruction of oxygen-carrying red blood cells (hemolytic anemia).
Interference with Antioxidants: Menadione can disrupt the function of glutathione, a vital antioxidant in the body, leading to increased oxidative stress and cellular damage.
Regulatory Ban: The FDA has banned menadione from use in human dietary supplements because of these severe adverse effects.

Where is Vitamin K3 Used?

Despite being unsafe for humans, vitamin K3 serves a purpose elsewhere. It is commonly used as a nutritional supplement in animal feed for livestock, such as poultry and pigs, as well as in commercial pet food for dogs and cats. In these applications, controlled dosages have not been shown to cause harm.

The Healthy, Natural Alternatives: K1 and K2

Instead of seeking out the dangerous synthetic version, focus on obtaining the two natural and beneficial forms of vitamin K from your diet: vitamin K1 (phylloquinone) and vitamin K2 (menaquinones).

Rich Dietary Sources of Vitamin K

Vitamin K1 (Phylloquinone): This is the most common form of vitamin K in the Western diet. It is produced by plants and is abundant in green leafy vegetables. To enhance absorption, eat these foods with a healthy fat source like olive oil or avocado.
- Kale (cooked)
- Spinach
- Collard and turnip greens
- Broccoli
- Brussels sprouts
- Soybean and canola oils
Vitamin K2 (Menaquinones): This form is primarily produced by bacteria and is found in fermented foods and certain animal products. A unique subtype, MK-4, is converted from K1 in the body.
- Natto (fermented soybeans)
- Hard and soft cheeses
- Eggs
- Pork and chicken

Comparison Table: Vitamin K1 vs. Vitamin K3


Feature	Vitamin K1 (Phylloquinone)	Vitamin K3 (Menadione)
Source	Naturally found in plants, especially green leafy vegetables.	Synthetically produced in a laboratory.
For Human Consumption?	Yes. It is safe and essential for human health.	No. It is toxic to humans and banned for this use.
Primary Function	Cofactor for blood clotting proteins and bone health.	Toxic analogue; can cause hemolytic anemia and liver damage.
Availability	Available through a wide variety of whole foods and supplements.	Used exclusively in animal feed applications.
Bioavailability	Can be less efficiently absorbed from plants without fat, but overall very safe and effective.	Toxic and not absorbed or utilized safely by the human body.

The Bottom Line on Sourcing Vitamin K

When you hear about vitamin K, it is crucial to recognize that the term refers to a family of compounds. The synthetic form, vitamin K3, is hazardous and has no place in human nutrition. The safe and healthy path to obtaining this essential nutrient is to consume a diverse diet rich in foods containing vitamins K1 and K2. Embracing natural sources ensures you benefit from vitamin K's positive effects on blood clotting and bone health without risking your well-being. By prioritizing a balanced diet, you can easily meet your daily vitamin K needs.

Disclaimer: Always consult with a healthcare professional before making any significant changes to your diet or taking supplements, especially if you are on blood-thinning medication.

Frequently Asked Questions

The primary difference is that vitamin K3 (menadione) is a synthetic, man-made version that is toxic to humans, while vitamin K1 (phylloquinone) and K2 (menaquinones) are natural forms found in foods.

No, you cannot buy vitamin K3 supplements for human use. Regulatory bodies, like the FDA in the U.S., have banned it due to its potential to cause severe adverse health effects.

Ingesting vitamin K3 can cause toxic reactions in humans, including liver damage, hemolytic anemia (destruction of red blood cells), and jaundice.

You can get safe vitamin K from food. Vitamin K1 is in leafy greens like spinach and kale, while vitamin K2 is found in fermented foods like natto, and in animal products such as eggs and certain cheeses.

Vitamin K3 is used in some animal feed for livestock and pets, where dosages are carefully controlled and regulated. It is not considered safe for human consumption in any amount.

Since vitamin K is a fat-soluble vitamin, consuming K1-rich vegetables alongside a source of healthy fat, such as avocado or olive oil, can help increase absorption.

No, while both are essential, they are different compounds with distinct roles. K1 primarily supports blood clotting, while K2 has a longer half-life and plays a greater role in bone and cardiovascular health.