Introduction: The “Koagulation” vitamin

Unlike most vitamins named in English, vitamin K takes its name from the German word "Koagulation", which hints at its primary function: helping your blood clot properly. Without it, even a minor injury could lead to dangerous bleeding.

But vitamin K’s story is far more fascinating than its name suggests. Its discovery was accidental, its benefits surprisingly far-reaching, and its evolution into modern medicine still ongoing.

An accidental discovery in Denmark

In 1929, Danish scientist Henrik Dam was researching cholesterol metabolism in chickens. He fed them a cholesterol-free diet, expecting to study lipid deficiencies. What he found instead was unexpected: the birds began bleeding internally, especially in their muscles and under their skin.

Oddly, this bleeding was not caused by trauma or infection. Dam concluded that the chickens were missing an unknown compound, a "coagulation vitamin," that was present in natural fats but missing from the refined diets. He called it vitamin K, after Koagulation.

The role of vitamin K in blood clotting

Vitamin K is essential for the production of prothrombin, a protein involved in blood coagulation. Without enough vitamin K, your body can’t form clots effectively. This usually leads to excessive bleeding and difficulty healing wounds.

For this discovery, Henrik Dam (along with Edward Doisy, who later isolated the compound) was awarded the Nobel Prize in Physiology or Medicine in 1943.

Two forms, one mission: K1 and K2

As research continued, scientists found that vitamin K exists in two major forms:

• Vitamin K1 (phylloquinone): Found in leafy greens; primarily supports blood clotting
• Vitamin K2 (menaquinone): Found in fermented foods and animal products; plays a key role in bone and cardiovascular health

K2 was discovered later, but it has gained increasing attention for its role in directing calcium to the bones and teeth, and away from arteries, where it can cause calcification.

Learn more about how vitamin K2 works synergistically with vitamin D in our post on vitamins that work better together.

Where to find vitamin K

Vitamin K1 (Phylloquinone)

Found mostly in green vegetables, including:

• Kale
• Spinach
• Broccoli
• Lettuce
• Brussels sprouts

Vitamin K2 (Menaquinone)

Found in fermented and animal-based foods, including:

• Natto (fermented soybeans—extremely high in K2)
• Hard cheeses
• Egg yolks
• Chicken and liver

Because vitamin K is fat-soluble, it’s best absorbed when eaten with healthy fats, just like vitamins A, D, and E.

Modern health benefits of vitamin K

In addition to clotting, vitamin K is now known to support:

• Bone density by activating osteocalcin, a protein that binds calcium to bones
• Heart health by reducing arterial calcification
• Cognitive health in aging populations (emerging area of research)
• Glucose metabolism and insulin sensitivity (especially K2)

How much do you need?

The Recommended Daily Intake for vitamin K1 is:

• Men: 120 mcg
• Women: 90 mcg

There is no official RDA for vitamin K2, but many health professionals recommend supplementing with 100–200 mcg of K2 for optimal bone and cardiovascular support, especially if taking calcium or D3.

Final thoughts: A vitamin still evolving

Vitamin K may have been discovered by accident, but its importance is anything but accidental. From blood clotting to bone strength and arterial protection, it’s a nutrient that deserves a place in every diet.

Its story reminds us that sometimes, science uncovers what we weren’t even looking for, and those surprises often save lives.

The end of the series, but just the beginning for your health

This concludes our Vitamin Origin Series, where we’ve uncovered the fascinating backstories behind:

• Vitamin A – The first vitamin ever discovered
• Vitamin B – The complex that solved mysterious diseases
• Vitamin C – The citrus cure that saved sailors
• Vitamin D – The sunshine remedy for bone health
• Vitamin E – The cell’s silent protector
• Vitamin K – The vitamin that quietly keeps your blood and bones strong

For more wellness insights, supplement guidance, and nutrient deep dives, continue exploring the Volta Santé blog.