Vitamin K1 vs. K2: What’s the Difference?

Vitamin K is a fat-soluble vitamin that helps your body make proteins needed for normal blood clotting and calcium metabolism. It’s a group of related compounds, and its two main forms are vitamin K1 and vitamin K2.

K1, also called phylloquinone, comes mainly from leafy greens such as spinach and kale. K2, also called menaquinone, comes from fermented foods like natto, as well as cheese and egg yolks.

Your body uses the two forms in different ways. K2 stays in circulation longer than K1, which is one reason it’s the form often paired with vitamin D3 in supplements.

Key Takeaways

• K1 comes mainly from leafy greens. K2 comes from fermented and animal foods, such as natto, cheese, and egg yolks.

• K2, especially the MK-7 form, stays in the body much longer than K1.

• K2 is often paired with vitamin D3 because both play a role in how your body uses calcium.

What Is Vitamin K?

Vitamin K is a fat-soluble vitamin. Your body uses it to switch on certain proteins so they can do their jobs. Two of those jobs stand out (Office of Dietary Supplements, n.d.-b):

• Normal blood clotting. Vitamin K helps the liver make prothrombin and other proteins that help blood clot normally. This role is most closely tied to K1.

• Calcium metabolism. Vitamin K activates osteocalcin, a protein in bone that binds calcium. This role is most closely tied to K2.

Vitamin K1 vs K2: What’s the Difference?

K1 and K2 share the same basic structure, but they differ in three practical ways: where they come from, how your body uses them, and how long they stay in your system.

Food Sources

K1, also called phylloquinone, is found mostly in green leafy vegetables. One cup of raw spinach has about 145 mcg, and one cup of raw kale has about 113 mcg. Soybean and canola oils also contain K1 (Office of Dietary Supplements, n.d.-b).

K2, also called menaquinone, comes mainly from fermented foods and some animal foods. Natto, a fermented soybean dish from Japan, is the richest source, with about 850 mcg in 3 ounces. Cheese and egg yolks contain smaller amounts. Bacteria in your gut also make some K2, though it is not clear how much of it your body absorbs (Office of Dietary Supplements, n.d.-b).

K1 from vegetables is bound tightly inside plant cells, so the body absorbs only 4% to 17% as much K1 from spinach as from a tablet. Eating greens with some fat, such as olive oil, improves absorption (Office of Dietary Supplements, n.d.-b).

How the Body Uses Each Form

Most vitamin K from food travels first to the liver (Beulens et al., 2013). K1 is cleared from the blood quickly, so the liver uses most of it to make the proteins involved in normal blood clotting.

K2, especially MK-7, stays in circulation much longer. That gives tissues outside the liver, such as bone, more time to take it up. In a trial in healthy adults, MK-7 led to more complete activation of osteocalcin, the calcium-binding protein in bone, than K1 did (Schurgers et al., 2007).

How Long Each Form Stays in the Body

K1 has a short half-life in the blood. MK-7 has a half-life of several days and is not fully cleared until about 72 to 96 hours after a dose (Beulens et al., 2013).

That longer stay adds up. In a trial comparing the two, daily MK-7 built up to blood levels 7 to 8 times higher than daily K1 (Schurgers et al., 2007). Steadier blood levels are one reason K2 is the form used in many supplements.

Is Vitamin K the Same as K2?

Not exactly. K2 is one form of vitamin K. All K2 is vitamin K, but not all vitamin K is K2.

A third form, vitamin K3 or menadione, is synthetic. It is not used in dietary supplements or fortified foods because lab studies linked it to liver cell damage (Office of Dietary Supplements, n.d.-b).

When a supplement label lists vitamin K, check which form it names. Phylloquinone means K1. Menaquinone, MK-4, or MK-7 means K2.

What Are the Types of Vitamin K2?

K2 is a family of compounds named for the length of their side chain, from MK-4 to MK-13. The two most common in supplements are MK-4 and MK-7 (Office of Dietary Supplements, n.d.-b).

MK-4

MK-4 is found in animal foods such as egg yolks and cheese. Your body can also make some MK-4 from K1 in certain tissues (Beulens et al., 2013). MK-4 is cleared from the blood very quickly. In a study of healthy women, a single 420 mcg dose of MK-4 taken with breakfast could not be detected in the blood at any point afterward (Sato et al., 2012).

MK-7

MK-7 comes mainly from natto, where bacteria make it during fermentation. It is well absorbed and lasts much longer. In the same study, an equal dose of MK-7 peaked in the blood after 6 hours and was still detectable 48 hours later (Sato et al., 2012). A second part of the study found the same pattern over a week: a small daily dose of MK-7 raised blood MK-7 levels in every participant, while MK-4 did not raise MK-4 levels.

Why Is Vitamin K2 Paired With Vitamin D3?

Vitamin D3 and K2 both help your body handle calcium, but they work at different steps.

Vitamin D3 helps your body absorb calcium from food in the intestines. It also helps keep calcium and phosphate levels in the blood steady, which supports normal bone mineralization (Office of Dietary Supplements, n.d.-a).

Vitamin K2 helps put that calcium to use. It activates osteocalcin, the protein that binds calcium into bone (Office of Dietary Supplements, n.d.-b). In simple terms, D3 helps bring calcium into the body, and K2 helps the body use that calcium to build bone.

Taking vitamin D3 with K2 covers both steps of calcium metabolism in one routine.

How to Get More Vitamin K2

K2 is harder to get from a typical Western diet than K1. Studies from the Netherlands and Germany estimate that K2 makes up only 10% to 25% of total vitamin K intake, with cheese as the main source (Beulens et al., 2013). The foods highest in K2 include:

• Natto: by far the richest source, mostly as MK-7.

• Cheese: the largest K2 source in many Western diets.

• Egg yolks: a source of MK-4.

• Other fermented foods: amounts vary with the bacteria and fermentation method.

Because K2 is fat-soluble, eating these foods with some fat helps your body absorb it (Office of Dietary Supplements, n.d.-b). Food databases mostly track K1, so most people have little idea how much K2 they eat. If natto is not part of your diet, a supplement is one way to add MK-7.

Rho Liposomal D3K2

Rho Liposomal D3K2 pairs vitamin D3 with vitamin K2 as MK-7 in one liposomal liquid. Liposomes are tiny spheres made from phospholipids, the same type of fat that forms cell membranes. Wrapping the vitamins in these spheres is a delivery format designed to support absorption.*

Using MK-7 means the formula provides the longer-lasting form of K2. Vitamin D3 supports calcium absorption, and K2 supports normal calcium metabolism and bone health.* See the product label for serving information.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Frequently Asked Questions

Do you need both vitamin K1 and K2?

Both forms have roles in the body. The Adequate Intake for vitamin K is 120 mcg a day for men and 90 mcg a day for women, and it does not separate K1 from K2 (Office of Dietary Supplements, n.d.-b). Most people get K1 from leafy greens, while K2 takes more intention, through foods like cheese, egg yolks, and natto.

Which form of vitamin K2 is best?

MK-7 stays in the blood much longer than MK-4 and remains detectable for up to 48 hours after a single dose (Sato et al., 2012). That is why MK-7 is the form used in most K2 supplements.

Can you take vitamin K2 without vitamin D3?

Yes. K2 can be taken on its own. Many people take the two together because they work at different steps of calcium metabolism. No upper limit has been set for vitamin K, because no harmful effects from food or supplements have been reported (Office of Dietary Supplements, n.d.-b). Talk with your healthcare provider before starting a new supplement.

What is the best time to take vitamin D3 and K2?

Both are fat-soluble, and fat in a meal helps your body absorb them (Office of Dietary Supplements, n.d.-a). Pairing your dose with a meal and taking it every day matters more than the time on the clock.

References

Office of Dietary Supplements. (n.d.-b). Vitamin K: Fact sheet for health professionals. National Institutes of Health. https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/

Beulens, J. W. J., Booth, S. L., van den Heuvel, E. G. H. M., Stoecklin, E., Baka, A., & Vermeer, C. (2013). The role of menaquinones (vitamin K2) in human health. British Journal of Nutrition, 110(8), 1357–1368. https://doi.org/10.1017/S0007114513001013

Schurgers, L. J., Teunissen, K. J. F., Hamulyák, K., Knapen, M. H. J., Vik, H., & Vermeer, C. (2007). Vitamin K-containing dietary supplements: Comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood, 109(8), 3279–3283. https://doi.org/10.1182/blood-2006-08-040709

Sato, T., Schurgers, L. J., & Uenishi, K. (2012). Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutrition Journal, 11, 93. https://doi.org/10.1186/1475-2891-11-93

Office of Dietary Supplements. (n.d.-a). Vitamin D: Fact sheet for health professionals. National Institutes of Health. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

 

*This article is for informational purposes only and is not a substitute for professional medical or nutritional advice.