How Was Vitamin K2 Discovered? A History of Menaquinone Research

January 9, 2026 •

3 min read

In 1929, Danish biochemist Carl Peter Henrik Dam, while studying cholesterol in chickens, observed a hemorrhagic disease that led to the discovery of a new nutrient he named 'Koagulations vitamin' or vitamin K. While Dam's initial work centered on this blood-clotting factor, the subsequent discovery of its distinct forms, particularly vitamin K2, reveals a much deeper and more complex nutritional story.

Quick Summary

The discovery of vitamin K2 was a process extending decades, beginning with the initial vitamin K research in the 1920s by Henrik Dam. American biochemist Edward Doisy later differentiated the two main forms, K1 and K2. Ongoing research has since unveiled the unique benefits of K2 for bone and cardiovascular health, particularly subtypes like MK-4 and MK-7 found in animal and fermented foods.

Key Points

Initial Discovery: In 1929, Henrik Dam first identified a fat-soluble 'koagulations vitamin' (later named vitamin K) by observing bleeding in fat-free fed chicks.
Differentiation into K1 and K2: Edward Doisy's subsequent research distinguished between vitamin K1 from plants (alfalfa) and vitamin K2 from animal and bacterial sources (fish meal).
Nobel Prize Recognition: Dam and Doisy shared the 1943 Nobel Prize for their foundational work on vitamin K and its chemical structure.
Unique K2 Functions: Unlike K1, which is primarily used for blood clotting, K2 was later found to play a vital role in extra-hepatic tissues like bones and blood vessels.
Role in Calcium Metabolism: Vitamin K2 activates proteins like osteocalcin and MGP, directing calcium to bones and preventing its accumulation in arteries.
Different Forms of K2: The most studied menaquinones (K2) are MK-4, found in animal products, and MK-7, abundant in fermented foods like natto.
Modern Health Significance: Contemporary research links adequate K2 intake with better cardiovascular health and bone density, expanding its known benefits beyond simple blood coagulation.

From Chickens to Cures: The Initial Discovery of Vitamin K

The story of vitamin K2's discovery begins with its predecessor, vitamin K. In the late 1920s, Danish scientist Henrik Dam conducted experiments on chicks, feeding them a fat-free diet to study cholesterol metabolism. The chicks developed a mysterious bleeding disorder, where their blood failed to coagulate properly. Upon reintroducing fat-soluble extracts from sources like hempseed, Dam found the hemorrhagic condition was reversed. He named the essential fat-soluble nutrient "Koagulations vitamin," which was eventually shortened to vitamin K. This groundbreaking work, which identified vitamin K's crucial role in blood clotting, earned him a share of the 1943 Nobel Prize in Physiology or Medicine.

The Differentiation of Vitamin K1 and K2

While Dam laid the foundation, it was Edward Adelbert Doisy, an American biochemist, who further refined the understanding of vitamin K. Working at Saint Louis University, Doisy's team successfully isolated and determined the chemical structure of vitamin K in 1939. It was through this work that researchers realized vitamin K was not a single compound but a family of related fat-soluble substances known as vitamers. Doisy was able to distinguish between two main forms: K1 (phylloquinone), isolated from plants like alfalfa, and K2 (menaquinone), isolated from fish meal and other animal products. For this crucial work, Doisy also shared the Nobel Prize with Dam.

Unlocking the Unique Benefits of Vitamin K2

For decades following the Nobel Prize, much of the research and medical focus remained on vitamin K's blood-clotting function. However, research later revealed that while K1 is primarily used by the liver for blood clotting factors, K2 plays a more significant role in extra-hepatic tissues like bones and blood vessels by activating specific proteins. This discovery was crucial in understanding K2's distinct benefits, particularly its role in calcium metabolism, where it helps prevent arterial calcification and promotes calcium integration into bone. Studies have since indicated a link between dietary K2 and reduced risk of heart disease.

Sources and Forms of Menaquinone (K2)

A Diversity of Menaquinones

Vitamin K2 is a group of compounds called menaquinones (MK-n). The most important forms are MK-4 and MK-7.

MK-4 (Menaquinone-4): Found in animal products, including meat, eggs, and dairy, particularly from grass-fed animals. The body can convert K1 to MK-4 in some tissues.
MK-7 (Menaquinone-7): Produced by bacteria and abundant in fermented foods like natto. MK-7 is noted for its high bioavailability and longer presence in the body.

How Vitamin K1 is Different from K2


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Source	Green leafy vegetables	Animal products and fermented foods
Body Distribution	Mainly liver	Soft tissues and bones
Primary Function	Blood coagulation	Bone mineralization and preventing arterial calcification
Bioavailability	Lower	Higher (especially MK-7)

The Evolution of Understanding

The understanding of vitamin K has evolved significantly. Initially focused on blood clotting, research later highlighted the distinct roles of K1 and K2. K2's specific functions in extra-hepatic tissues have led to new research into its impact on bone, cardiovascular, and neurological health. The better bioavailability of forms like MK-7 from natto has established K2 as a unique and important nutrient, separate from its initial link to blood coagulation.

A Complex and Continual Discovery

The discovery of vitamin K2 was a process built upon the work of multiple researchers over many years. The initial focus on blood clotting expanded to recognize its broad impact on health and the distinct roles of different vitamers. This journey from the "koagulations vitamin" to a key nutrient for bone and heart health continues to drive scientific interest. Differentiating K1 and K2 has fundamentally changed nutritional science, emphasizing the importance of both for health.

Visit the Nobel Prize website for more information on the award presented to Dam and Doisy

Frequently Asked Questions

Vitamin K1 (phylloquinone) is found in green leafy plants and is mainly used by the liver for blood clotting, while vitamin K2 (menaquinone) is found in animal and fermented foods and works primarily in extra-hepatic tissues to support bone and cardiovascular health.

Danish biochemist Carl Peter Henrik Dam discovered vitamin K in the late 1920s through experiments with chicks that developed bleeding problems on a cholesterol-free diet.

American biochemist Edward Adelbert Doisy and his team were responsible for isolating and determining the chemical structure of the different vitamin K forms in the late 1930s, distinguishing K1 from K2.

Primary sources of vitamin K2 include animal products like eggs and meat, particularly from grass-fed sources, and fermented foods like the Japanese dish natto, which is rich in the MK-7 subtype.

Dam called it 'vitamin K' for 'Koagulations vitamin' after its discovery involving blood coagulation, as he published his initial findings in a German journal.

Menaquinone-7 (MK-7), often derived from natto, is a popular form in supplements due to its higher bioavailability and longer half-life compared to vitamin K1.

Vitamin K2 helps activate osteocalcin, a protein that binds calcium into the bone matrix, which is essential for building and maintaining strong, dense bones.