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What is the difference between vitamin K and vitamin K2?

Vitamin K is an essential nutrient that plays an important role in blood clotting and bone health. There are several forms of vitamin K, with the two major ones being vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). While both are crucial for health, research shows that vitamin K2 offers unique benefits that vitamin K1 does not. This article will explore the key differences between vitamin K1 and K2, their sources, functions and health impacts.

What is Vitamin K1?

Vitamin K1, also known as phylloquinone, is the form of vitamin K that is found in plant foods. The highest concentrations are found in leafy green vegetables like kale, spinach, broccoli, Brussels sprouts, and lettuce. Other good plant-based sources include avocado, kiwi, grapes, edamame and olive oil.

Vitamin K1 is fat-soluble and gets absorbed with dietary fats present in the small intestine. Once absorbed, it accumulates in the liver where it supports blood clotting. Specifically, vitamin K1 is essential for the carboxylation of certain glutamic acid residues on blood clotting factors II (prothrombin), VII, IX and X. This carboxylation allows them to bind calcium, which initiates the blood clotting cascade. Without adequate vitamin K1 intake, blood clotting can be impaired.

The current adequate intake (AI) level for vitamin K1 is 90 micrograms per day for women and 120 micrograms per day for men. The AI provides enough to maintain adequate blood clotting factors. Vitamin K1 deficiency is rare, as the AI can be easily met through the diet. Deficiency symptoms include easy bruising, heavy menstrual bleeding and nosebleeds.

What is Vitamin K2?

Vitamin K2 refers to a group of compounds known as menaquinones. There are several different types of vitamin K2 (MK-4 through MK-13) based on the length of their side chains. Like vitamin K1, K2 is fat-soluble. However, its sources and functions differ.

The best dietary sources of vitamin K2 include:

  • Natto (fermented soybeans)
  • Some cheeses like brie, gouda and edam
  • Egg yolks
  • Meat and poultry
  • Animal-based foods like butter and chicken liver

Vitamin K2 can also be produced by gut bacteria and absorbed into the bloodstream. However, the amount produced in this way is generally insufficient to meet needs.

While vitamin K2 does support blood clotting like K1, studies show its main role is protecting bone and heart health. It activates proteins that put calcium into bones and teeth and keep it from accumulating in arteries or soft tissues. Specifically, vitamin K2 carboxylates the proteins osteocalcin (bone) and matrix-Gla protein (arteries).

No official dietary recommendations have been established for vitamin K2 due to limited data. However, studies suggest intakes of 45-185 mcg per day for adults help optimize bone and heart health. Deficiency is uncommon but increases fracture and heart disease risk.

Key Differences Between Vitamin K1 and K2

Here is an overview of the main differences between vitamins K1 and K2:


  • Vitamin K1: Found primarily in leafy greens and some plant oils.
  • Vitamin K2: Found primarily in animal foods and fermented soybeans (natto). Also produced by gut bacteria.

Main Functions

  • Vitamin K1: Supports blood clotting.
  • Vitamin K2: Protects bone and heart health.

Deficiency Effects

  • Vitamin K1: Impaired blood clotting, easy bruising.
  • Vitamin K2: Increased fracture and heart disease risk.

Dietary Recommendations

  • Vitamin K1: 90 mcg a day for women, 120 mcg for men.
  • Vitamin K2: No official recommendations, but intakes of 45-185 mcg are suggested.

Absorption and Transport

  • Vitamin K1: Absorbed in the small intestine and accumulates in the liver.
  • Vitamin K2: Absorbed in the small intestine and accumulates in bones and arteries.

Vitamin K1 vs K2: Key Health Differences

Though vitamins K1 and K2 are both critical for health, research demonstrates that K2 offers unique benefits:

Bone Health

Several studies have found that vitamin K2 supplementation significantly improves bone density and reduces fracture risk, while vitamin K1 has no effect. For example, a 3-year study in 244 postmenopausal women found that doses of 45 mcg per day of vitamin K2 as MK-4 reduced age-related bone loss, while vitamin K1 did not.

Researchers believe this bone-protective effect is mediated via vitamin K2’s activation of the osteocalcin protein.

Heart Health

By activating matrix GLA protein, vitamin K2 helps prevent calcium accumulation in blood vessels and lowers risk of arterial calcification. In one major study in 4,807 adults, high vitamin K2 intake was linked to a 57% lower risk of severe arterial calcification and a 51% lower risk of heart disease mortality. Vitamin K1 intake showed no heart benefits.

Other studies found vitamin K2 (but not K1) supplementation significantly reduced arterial stiffness and protected against vascular calcification in patients with kidney disease.


Several population studies have linked higher dietary intakes of vitamin K2 (MK-4), but not vitamin K1, with a lower risk of cancer. For example, one study in 11,000 adults found that high MK-4 intake was associated with a 63% decreased risk of liver cancer. More research is needed on K2’s potential anti-cancer effects.

Should You Supplement With Vitamin K2?

Current evidence suggests that supplementation with small doses of vitamin K2 (45-185 mcg per day) may be beneficial, especially for bone and heart health, unless you regularly eat K2-rich foods like natto, cheese and meat.

Supplements are widely available in capsule form or as oils and typically provide MK-4 and/or MK-7 types of vitamin K2. MK-7 supplements may provide better absorption compared to MK-4.

As with any supplement, it’s best to speak with a healthcare provider before starting to make sure it’s appropriate for your needs. Ensure they are aware of any medications or health conditions, as vitamin K can interact with blood thinners like warfarin.

Additionally, make sure to maintain adequate vitamin K1 intake from leafy greens and plant oils. Vitamin K1 remains crucial for proper blood clotting.

The Bottom Line

In summary:

  • Vitamin K1 is found in plants, supports blood clotting and is recommended at 90-120 mcg/day.
  • Vitamin K2 is found in animal foods and fermented soy, supports bone and heart health, and optimal intakes are 45-185 mcg/day.
  • Research shows vitamin K2 specifically benefits bone density, arterial health and may lower cancer risk, while K1 does not.
  • Consider supplementing with small doses of vitamin K2 after consulting a healthcare provider, in addition to eating K1-rich foods.

Getting adequate amounts of both vitamin K1 and K2 from the diet or supplements ensures good blood clotting while also promoting strong bones and a healthy heart.