Natural and Synthetic Vitamin K: Understanding the Differences

Over 75% of vitamin K consumed by humans comes from the plant-based, natural form known as vitamin K1. Vitamin K, a critical fat-soluble vitamin, exists in multiple forms, both natural and synthetic, and understanding their unique roles is key for optimal health.

Quick Summary

This guide details the primary natural forms, vitamin K1 (phylloquinone) and vitamin K2 (menaquinone), and the synthetic variant, vitamin K3 (menadione). It covers their sources, how the body uses them, and the distinct health implications of each type.

Key Points

• Natural Vitamin K exists in two forms: K1 (phylloquinone), found in plants, and K2 (menaquinones), produced by bacteria and found in fermented foods and animal products.

• Synthetic Vitamin K3 (Menadione) is toxic for humans: It has been associated with liver damage and hemolytic anemia, leading to its removal from human supplements.

• Functional differences exist between K1 and K2: K1 primarily aids liver-based blood clotting, while K2 is critical for calcium regulation in extra-hepatic tissues, promoting bone density and preventing arterial calcification.

• K2 has better bioavailability than K1: Long-chain menaquinones like MK-7 are absorbed more efficiently and remain in circulation longer than K1, allowing for better tissue distribution.

• Dietary intake is usually sufficient: Most healthy adults can meet their vitamin K needs through a balanced diet, making severe deficiency rare.

• Consult a doctor about supplementation: Individuals on anticoagulant therapy (like warfarin) must maintain a consistent vitamin K intake and should consult a healthcare provider before taking supplements.

Introduction to the Vitamin K Family

Vitamin K is a group of structurally similar, fat-soluble vitamins essential for several physiological processes, primarily blood coagulation and bone metabolism. While its role in preventing excessive bleeding is widely known, different forms of vitamin K offer distinct benefits and carry varying health considerations. For example, studies suggest that some forms of vitamin K2 may be more effective for heart and bone health than vitamin K1. The main types are the natural K1 (phylloquinone) and K2 (menaquinones), and the synthetic K3 (menadione).

Natural Vitamin K: K1 and K2

There are two primary forms of natural vitamin K, both playing critical roles in the body. The main differences lie in their food sources, chemical structure, and how the body absorbs and distributes them.

Vitamin K1 (Phylloquinone)

Vitamin K1 is the most common form of dietary vitamin K and is primarily sourced from plants. In the body, K1 is primarily used by the liver to activate proteins involved in blood clotting.

Sources of Vitamin K1:

• Leafy green vegetables, such as kale, spinach, collard greens, and broccoli.
• Vegetable oils, including soybean and canola oil.
• Some fruits, like blueberries, grapes, and prunes.

Vitamin K2 (Menaquinone)

Vitamin K2 comprises several subtypes, known as menaquinones (MK-4 through MK-13), which are produced by bacteria. K2 is transported to extrahepatic tissues like bones and arteries, where it activates proteins for calcium regulation, preventing arterial calcification and promoting healthy bone tissue.

Sources of Vitamin K2:

• Fermented foods, most notably the Japanese dish natto, made from fermented soybeans, is an exceptionally rich source of MK-7.
• Certain cheeses and other fermented dairy products.
• Animal products like egg yolks, butter, and organ meats contain MK-4.
• Bacteria in the gut also produce some menaquinones.

How natural vitamin K is produced

Natural vitamin K is not synthesized by humans but derived from dietary sources and bacterial synthesis. Vitamin K1 is naturally synthesized by plants. Different forms of vitamin K2 are produced by bacteria through fermentation. For example, the fermentation of soybeans by Bacillus subtilis natto produces large amounts of MK-7.

Synthetic Vitamin K: K3 (Menadione)

Synthetic vitamin K3, or menadione, is a water-soluble compound not found in nature that can be converted to K2 in the liver. Historically, it was used in supplements, but safety concerns have largely led to its prohibition for human consumption in many countries.

Harmful Effects and Toxicity

Unlike the natural forms, vitamin K3 has demonstrated toxicity in humans. Studies from the 1980s and 1990s linked it to liver damage and the destruction of oxygen-carrying red blood cells. The potential side effects, especially in infants, include hemolytic anemia and jaundice. Today, synthetic K3 is primarily used in animal feed.

How synthetic vitamin K is produced

Synthetic vitamin K forms like menadione are produced through chemical synthesis in laboratory and industrial settings. These processes involve combining specific precursor compounds, such as 2-methyl-1,4-naphthoquinone, with other reagents to create the desired vitamin K analog. This differs significantly from the natural plant-based or bacterial production methods.

Comparison: Natural vs. Synthetic Vitamin K

Feature	Natural Vitamin K (K1 & K2)	Synthetic Vitamin K (K3)
Source	Plants (K1), fermented foods, and gut bacteria (K2).	Chemically manufactured.
Structure	K1 has a saturated phytyl side chain, while K2 has unsaturated isoprenoid side chains (menaquinones).	Lacks a side chain; can be considered a provitamin.
Toxicity	Very low potential for toxicity in humans, with no established upper intake level.	Associated with toxicity in humans, including liver damage and hemolytic anemia.
Primary Function	K1: mainly blood clotting in the liver; K2: calcium regulation for bone and cardiovascular health.	Potentially converted to K2 in the liver, but not used in human supplements due to safety concerns.
Supplement Availability	Commonly available as safe dietary supplements, especially as K1 (phytonadione) and K2 (MK-4, MK-7).	Not legally sold as a supplement for human consumption in many places, including the U.S..

Conclusion

Understanding the differences between natural and synthetic vitamin K is essential for making informed health decisions. The natural forms, K1 and K2, are safe and crucial for numerous bodily functions, with K1 primarily supporting blood clotting and K2 playing a key role in bone and cardiovascular health. In contrast, the synthetic form, K3 (menadione), has known toxic effects in humans and is not recommended or sold for human consumption. While a balanced diet rich in leafy greens and fermented foods typically provides sufficient natural vitamin K, supplements containing safe, natural forms like K1 and K2 are widely available for those who need them.

For more detailed information on vitamin K and its dependent proteins, refer to the academic review "Vitamin K: Double Bonds beyond Coagulation Insights into the Non-Coagulant Roles of Vitamin K" from PubMed Central.

Keypoints

• Natural Vitamin K comes in two main types: Vitamin K1 (phylloquinone) from plants and Vitamin K2 (menaquinone) from fermented foods, animal products, and gut bacteria.
• Natural K1 and K2 have different functions: K1 is primarily used by the liver for blood clotting, while K2 is distributed to extra-hepatic tissues to regulate calcium for bone and heart health.
• Synthetic Vitamin K3 (Menadione) is toxic: It has been linked to liver damage and other adverse effects in humans and is not approved for use in dietary supplements.
• Absorption and bioavailability differ: K2, particularly the MK-7 subtype, tends to have better absorption and a longer half-life in the body compared to K1.
• A balanced diet is key: Most people can obtain sufficient natural vitamin K from eating a variety of green leafy vegetables and fermented foods.
• Supplementation considerations exist: Individuals on blood-thinning medications like warfarin should consult a doctor before changing their vitamin K intake due to potential interactions.

Faqs

• What are the primary natural forms of vitamin K? The two main natural forms are vitamin K1 (phylloquinone), found in green leafy vegetables, and vitamin K2 (menaquinones), found in fermented foods and animal products.
• Why is synthetic vitamin K3 (menadione) not safe for humans? Menadione has been shown to cause liver damage and destroy red blood cells in humans, leading to its ban from dietary supplements.
• What is the main difference in function between natural K1 and K2? Vitamin K1 primarily focuses on blood clotting factors in the liver, whereas K2 is involved in activating proteins that regulate calcium, benefiting bone and arterial health.
• Are all menaquinone (K2) subtypes the same? No, K2 has different subtypes (MK-4 to MK-13) with varying side chain lengths. MK-4 and MK-7 are the most studied, with MK-7 known for its better absorption and longer circulation time.
• Can I get enough vitamin K from my diet alone? For most healthy individuals, a balanced diet rich in green leafy vegetables (for K1) and some fermented foods or animal products (for K2) provides adequate intake. Deficiency is rare in adults.
• Who might benefit from a natural vitamin K supplement? Individuals with malabsorption disorders, those on long-term antibiotics, or those with specific health conditions should discuss supplementation with a healthcare provider.
• Do natural vitamin K supplements interfere with medications? Yes, particularly for those on anticoagulant medications like warfarin, a consistent vitamin K intake is critical. Sudden changes from supplements can interfere with the medication's effectiveness.

Citations

• Healthline. (2020). Vitamin K3 (Menadione): Benefits, Uses, and Side Effects. https://www.healthline.com/nutrition/vitamin-k3-menadione
• ScienceDirect Topics. (n.d.). Vitamin K - an overview. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/vitamin-k
• PubMed Central. (2017). Vitamins K1 and K2: The Emerging Group of Vitamins That Should Be on Every Clinician’s Radar. https://pmc.ncbi.nlm.nih.gov/articles/PMC5494092/
• NCBI Bookshelf. (2023). Vitamin K. https://www.ncbi.nlm.nih.gov/books/NBK551578/
• PubMed Central. (2019). Vitamin K: Double Bonds beyond Coagulation Insights into the Non-Coagulant Roles of Vitamin K. https://pmc.ncbi.nlm.nih.gov/articles/PMC6413124/

Frequently Asked Questions

What is the difference between natural vitamin K1 and K2?

Vitamin K1 (phylloquinone) is found in plants like leafy greens and is primarily used by the liver for blood clotting. Vitamin K2 (menaquinones) is found in fermented foods and animal products, and is produced by gut bacteria; it is more involved in regulating calcium for bone and heart health.

Why is synthetic vitamin K3 banned for human use?

Synthetic vitamin K3 (menadione) is toxic to humans and can cause liver damage and red blood cell destruction. Due to these adverse effects, it is not used in dietary supplements or fortified foods for human consumption.

What are the main food sources of vitamin K1?

Primary food sources of vitamin K1 include leafy green vegetables such as kale, spinach, and broccoli, as well as some vegetable oils like soybean and canola oil.

Where can I find dietary sources of vitamin K2?

Vitamin K2 is most abundant in fermented foods like natto and certain cheeses. It is also found in smaller amounts in animal products such as egg yolks, meat, and butter.

Which form of vitamin K is better for bone health?

Research suggests that vitamin K2, particularly the long-chain forms like MK-7, is more effective for bone health than K1 because it is better absorbed and transported to extra-hepatic tissues like bone, where it activates proteins for bone mineralization.

Is there a risk of taking too much natural vitamin K?

High doses of natural vitamin K from food or supplements have a very low potential for toxicity. As a result, no Tolerable Upper Intake Level (UL) has been established for K1 or K2. However, interactions with anticoagulant drugs are a concern.

What is phytonadione?

Phytonadione is the synthetic form of vitamin K1. It is used in dietary supplements and for medical purposes, such as preventing bleeding in newborns.