What was vitamin K isolated from? A Historical Look at its Discovery

January 11, 2026 •

3 min read

In 1929, Danish biochemist Henrik Dam observed that chickens fed a fat-free diet developed severe, spontaneous hemorrhages. This discovery ultimately led to the isolation of vitamin K from alfalfa, and marked a pivotal moment in nutritional science.

Quick Summary

Danish biochemist Henrik Dam discovered vitamin K in the 1930s while studying bleeding disorders in chickens. The initial form, vitamin K1, was isolated from green plants like alfalfa, while the chemical structure was later determined by Edward Doisy's team.

Key Points

Initial Discovery: Danish biochemist Henrik Dam discovered vitamin K's existence in the late 1920s through experiments on chicks with a fat-free diet.
Alfalfa Isolation: Dam and his colleagues isolated the first form, vitamin K1 (phylloquinone), from alfalfa in the 1930s.
Chemical Structure: Edward Adelbert Doisy and his team determined the chemical nature of vitamin K1 and K2, work that earned them a shared Nobel Prize with Dam in 1943.
Diverse Sources: While K1 comes from green plants, K2 (menaquinones) is produced by bacteria in fermented foods like natto and also found in animal products.
Broader Function: Beyond its role in blood coagulation, later research revealed vitamin K's critical functions in bone health and preventing arterial calcification.
Nomenclature: The 'K' in vitamin K comes from the German term for coagulation, "Koagulations-Vitamin".

The First Clues: The Koagulations-Vitamin

In the late 1920s, Dr. Henrik Dam of the University of Copenhagen began experiments on cholesterol metabolism in chicks using a fat-free and cholesterol-free diet. He observed that the chicks developed severe bleeding problems and their blood clotting time was significantly prolonged. Adding purified cholesterol didn't resolve the issue, leading Dam to propose that another fat-soluble compound was missing from the diet.

The Search for the Anti-Hemorrhagic Factor

Dam identified this unknown substance as essential for blood coagulation and named it "Koagulations-Vitamin," using the letter 'K' from the German spelling. He found this fat-soluble factor in green vegetables and liver, noting that these sources could correct the clotting defect in his test animals. The 1930s saw a scientific push to isolate and identify this compound.

Isolation from Alfalfa and Chemical Elucidation

The isolation of vitamin K was achieved through collaborative and independent efforts. Henrik Dam's team successfully isolated a substance from lucerne (alfalfa) that effectively treated the bleeding in chickens. Concurrently, the research group led by American biochemist Edward Adelbert Doisy at Saint Louis University undertook the detailed work to determine the precise chemical structure of this compound.

Doisy's Contribution and the Nobel Prize

Doisy and his colleagues made significant advancements in understanding the chemical structure of vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). Their findings, published in 1939, paved the way for synthetic production. For their pivotal roles in the discovery, isolation, and structural analysis of vitamin K, Dam and Doisy shared the Nobel Prize in Physiology or Medicine in 1943.

Diverse Natural Sources of Vitamin K

Vitamin K is now understood to be a group of fat-soluble compounds, known as vitamers, rather than a single entity. The two main forms found naturally are vitamin K1 (phylloquinone) and vitamin K2 (menaquinone).

Plant-Based Phylloquinone (Vitamin K1)

Phylloquinone is found in green plants and plays a role in photosynthesis. Rich dietary sources of vitamin K1 include green, leafy vegetables like spinach, kale, broccoli, Brussels sprouts, cabbage, and lettuce, as well as soybean and canola oils.

Bacterially Produced Menaquinones (Vitamin K2)

Menaquinones are synthesized by bacteria and are the primary form stored in animals. There are various menaquinone subtypes (MK-n), differing in their side chain length, with MK-4 and MK-7 being prominent. Menaquinones are present in fermented foods and animal products.

Fermented Foods: Natto, a Japanese dish of fermented soybeans, is an especially rich source of MK-7. Certain cheeses also contain menaquinones.
Animal Sources: Meat, eggs, and dairy provide varying levels of menaquinones. Chickens can convert vitamin K1 to MK-4, making poultry a source.

Comparison: Vitamin K1 vs. Vitamin K2


Feature	Vitamin K1 (Phylloquinone)	Vitamin K2 (Menaquinone)
Primary Source	Green plants, leafy vegetables	Fermented foods and animal products
Producer	Plants	Bacteria (e.g., in fermented foods, gut flora)
Chemical Side Chain	Phytyl group (single-double bond)	Polyisoprenoid chain (variable length)
Main Function	Liver activation of clotting factors	Calcium metabolism, bone and cardiovascular health
Bioavailability	Lower absorption from food, shorter half-life	Generally higher bioavailability, longer half-life (especially MK-7)
Body Transport	Chylomicrons, taken up mostly by liver	Also in VLDL/LDL, transported to extra-hepatic tissues

The Function of Vitamin K: Beyond Coagulation

While initially recognized for its role in blood clotting, vitamin K's functions are more extensive. It acts as a coenzyme for the carboxylation of specific proteins, a process vital for their proper function. This includes activating blood clotting factors produced in the liver, as well as proteins crucial for bone health like osteocalcin and those preventing arterial calcification, such as Matrix Gla protein (MGP). These additional roles, discovered later, underscore vitamin K's complex importance in health.

Conclusion: A Testament to Scientific Observation

The history of what was vitamin K isolated from highlights the impact of meticulous scientific inquiry. Henrik Dam's observations of bleeding in chicks on a specific diet led to the identification of a crucial fat-soluble factor and its isolation from alfalfa. Edward Doisy's subsequent work to determine the chemical structure was equally critical, culminating in a shared Nobel Prize. This journey from an initial observation to understanding vitamin K's various forms (K1 and K2) and their vital roles in coagulation, bone health, and cardiovascular function illustrates the progressive nature of nutritional science. The initial, insightful observation was fundamental to uncovering the significance of this essential nutrient.

Visit the official Nobel Prize website for more information on the award presented to Dam and Doisy for their contributions to the understanding of Vitamin K.

Frequently Asked Questions

Vitamin K1, also known as phylloquinone, was initially isolated from alfalfa (lucerne) and is found naturally in green leafy vegetables like spinach, kale, and broccoli.

Vitamin K1 is predominantly found in green plants and is essential for blood clotting. Vitamin K2, produced by bacteria, is found in fermented foods and animal products, and plays a more significant role in bone and cardiovascular health.

The initial discovery and isolation of vitamin K were led by Danish biochemist Henrik Dam, while American biochemist Edward Adelbert Doisy later elucidated its chemical structure.

Dam named it vitamin K because his initial findings were published in a German journal where it was designated the "Koagulations-Vitamin," after the German word for coagulation.

No. The vitamin K from plants is K1 (phylloquinone). The vitamin K produced by bacteria in your gut is K2 (menaquinone). Both have different structures and functions.

The chickens were fed a fat-free and cholesterol-depleted diet. It was the lack of a fat-soluble substance in this diet that led to the observed bleeding problems.

Vitamin K1 is abundant in green leafy vegetables, while vitamin K2 is found in fermented foods (like natto) and animal-based products (like meat, cheese, and eggs).

Individuals who eat more green leafy vegetables will have a higher intake of vitamin K1. People consuming fermented foods and animal products will have a higher intake of vitamin K2.