A common question many people ask is “What is vitamin K?” and what’s the difference between vitamin K1 vs. K2? 

Since its discovery in 1929, vitamin K has been known for its necessity in blood clotting.* In fact, it was named vitamin K for that very reason. The new vitamin received the designation “K” because its discovery was reported in a German medical journal in which it was designated as “Koagulationsvitamin.”

Although the question of what does vitamin K do in your blood is a crucial one – activating proteins necessary for blood clotting* ‒ vitamin K does much more. Two other primary therapeutic benefits – supported by an increasing body of research – are bone and blood vessel health.*

Multiple proteins important for bone and blood vessel health require vitamin K to function properly.*

Vitamin K is necessary to activate the proteins that are involved in:


Blood clotting*
Prothrombin/other clotting factors

Slowing of arterial calcification*
Matrix Gla-protein (MGP

Bone building*
Osteocalcin and calbindin

In the most basic terms, vitamin K is necessary to support clean arteries and strong bones.*

What really is vitamin K?

Vitamin K is actually several vitamins – K1, K2, and K3. Vitamins K1 and K2 are used in nutritional supplements. 

Vitamin K1, also known as phylloquinone, is widely found in plants.

Vitamin K2, also known as menaquinone, found more often in animal products, is a group of several different molecules that are identified based on the length of their side chains – from MK-2 to MK-14. The two forms of vitamin K2 most often used in nutritional supplements are MK-4 and MK-7.

Vitamin K3 is synthetic and has primarily been used in clinical investigations in cancer research, but it is not sold as a nutritional supplement in the United States.

Who should be taking vitamin K?

Although it is common to draw a distinction between vitamin K1 vs. K2, their effects on the body overlap extensively, and we’ll use the term vitamin K below to refer to both forms.

Vitamin K is so essential for bone and vascular health it’s hard to identify an individual who would not benefit from its supplementation.*

You might especially benefit from vitamin K supplementation if:

  • You regularly take an antacid
  • You take a statin for cholesterol management (recent research suggests statins can cause a vitamin K deficiency1)
  • You have a GI problem that causes fat malabsorption because vitamin K is fat-soluble
  • You have been taking an antibiotic, because, in addition to diet or supplement sources, vitamin K2 is produced by gut bacteria
  • You take a weight loss medication that inhibits fat absorption (like over-the-counter Alli® or prescription Xenical®)
  • You supplement with vitamin D or calcium, because vitamin K helps direct calcium to the bones and away from soft tissues like arteries where you don’t want it*
  • You are a peri- or postmenopausal woman – a time when bone and cardiovascular health can suffer
  • You are pregnant or trying to conceive (be sure vitamin K is in your prenatal vitamin)
  • You are concerned about your bone or cardiovascular health*

How much vitamin K is needed?

It was previously believed that the body needed only a tiny amount of vitamin K because that was all that was needed for blood coagulation. 

However, unlike its need in activating blood clotting proteins, higher levels of vitamin K are essential for the activation of other proteins, such as osteocalcin for bone health.* 

For example, in one study, the dietary intake of vitamin K in 219 healthy adults eating an average American diet was insufficient for osteocalcin activation, even though normal clotting (measured by prothrombin time) was maintained.2

Thus, it appears that a higher level of vitamin K is needed to support bone and vascular health compared to the level needed for blood clotting.*

But the ideal vitamin K dosage for adults is not a one-size-fits-all answer because it depends on the form of vitamin K.

Taking both vitamin K1 and vitamin K2 is the best way to ensure adequacy. Thorne’s Vitamin K contains vitamin K1 and two types of vitamin K2 – MK-4 and MK-7 – in a convenient once-daily capsule.

The health benefits of vitamin K1 appear to be achieved at daily amounts of several hundred micrograms (mcg) to a few milligrams (mg).

Vitamin K2 in the MK-7 form is best supplemented in the range of 90 to 180 mcg; whereas, vitamin K2 in the MK-4 form is typically supplemented with higher amounts – 5 mg and above. So, how much vitamin K per dayh is optimal? This depends on the individual's age, health status, lifestyle, and health goals.

What about dietary sources of vitamin K?

Dietary sources of vitamin K1 vs. K2 differ. 

Vitamin K1 is found in its highest concentration in green leafy vegetables, although it might not be very well absorbed from these sources. For example, one study found 6-times greater absorption of vitamin K1 from a nutritional supplement than from green vegetables like spinach, broccoli, and romaine lettuce.3

Vitamin K2 in the MK-4 form is found in butter, meat, eggs, and cheeses – particularly aged cheese. Gouda and brie are reported to be the cheeses with the highest amount of the MK-4 form.

Vitamin K2 in the MK-7 form is found in fermented foods, most notably natto, a traditional Japanese food made from fermented soybeans. 

The amounts of vitamin K2 in animal products and fermented vegetables vary widely. For example, some reports suggest dairy products from grass-fed cows and eggs from free-range chickens have higher amounts of vitamin K2 than grain-fed cows and chickens. Vitamin K2 is also produced by gut bacteria.

Because of the unreliability of dietary vitamin K content and its absorption, a nutritional supplement should be considered.

How is vitamin K absorbed and how long does vitamin K stay in your system?

Vitamin K is absorbed in the small intestine. Because it’s a fat-soluble vitamin, its absorption requires bile and pancreatic enzymes. Thus, taking a vitamin K supplement along with some fat in a meal is the best way to assure absorption.

Regarding, how long does vitamin K stay in your system – it depends on the form of vitamin K – vitamin K1 vs. K2. Unlike other fat-soluble vitamins, vitamin K1 is rapidly metabolized and excreted from the body within several hours. On the other hand, vitamin K2, because its chemical structure is comprised of long side chains, can take several days to be fully metabolized.

Can too much vitamin K cause blood clots?

Generally, the answer is no. However, if you have a concern, then consult with your health-care professional, particularly if you have a blood clotting issue or are taking an anticoagulant medication.

If you supplement vitamin D, don’t forget the K

Just like salt goes with pepper, and wine goes with chocolate, and magnesium goes with calcium, vitamin K goes with vitamin D. Vitamin K supplementation should always be paired with supplemental vitamin D when possible.

Although vitamin D increases the absorption of calcium to provide important support for bone health, vitamin K directs that absorbed calcium to the bones and not to the soft tissues, such as the blood vessels and the kidneys.*

References

  1. Chen Z, Qureshi AR, Parini P, et al. Do statins promote vascular calcification in chronic kidney disease? Eur J Clin Invest 2017;47(2):137-148.
  2. Binkley NC, Krueger DC, Engelke JA, et al. Vitamin K supplementation reduces serum concentrations of under-gamma-carboxylated osteocalcin in healthy young and elderly adults. Am J Clin Nutr 2000;72:1523-1528. 
  3. Garber AK, Binkley NC, Krueger DC, Suttie JW. Comparison of phylloquinone bioavailability from food sources or a supplement in human subjects. J Nutr 1999;129:1201-1203.