Myths About Vitamin K2

Over the past decade, vitamin K2 has transformed from a little-known molecule into one of the most heavily advertised supplements. It is called "the vitamin for the vessels," "the calcium conductor," and a mandatory companion to vitamin D. Some of these claims have a scientific basis, some do not. The editorial team examined the most common myths and separated the proven from the marketing.

Myth 1: vitamin K2 "cleans" calcium out of the vessels

The loudest promise of manufacturers is that K2 supposedly dissolves calcifications already present in the arteries. The logic is this: the vitamin activates matrix Gla-protein (MGP), which inhibits calcium deposition in the vessel walls. This is indeed true at the level of biochemistry: in mice without functional MGP, massive calcification of the arteries develops, as shown by Luo and colleagues back in 1997.

However, from the fact that MGP prevents calcification, it does not follow that a K2 supplement is able to remove it. In humans there is no evidence of reversal of atherosclerotic plaques or calcifications. Randomized studies for the most part assessed intermediate indicators — the level of the inactive form of MGP (dp-ucMGP) or arterial stiffness — rather than an actual reduction of calcium.

A study by Knapen and colleagues (2015) in postmenopausal women showed that three years of MK-7 intake improved arterial stiffness indicators in some of the participants. This is an interesting signal, but it is not equivalent to "cleaning" the vessels and does not prove a reduction in the risk of heart attack or stroke.

Observational data from the Rotterdam Study (Geleijnse et al., 2004) linked a higher dietary quota of menaquinones with lower mortality from ischemic heart disease. But such works reveal associations, not cause-and-effect relationships: people who eat more cheese and fermented products may also differ in many other respects.

Myth 2: K2 thickens the blood and causes clots

Since vitamin K is known as the "clotting vitamin," many people fear that a supplement will increase the risk of thrombosis. In fact, vitamin K only ensures the carboxylation of clotting factors — it helps them become functional but does not make the body produce them in excess. In a healthy person with adequate vitamin K status, the factors are already fully active.

This is confirmed by clinical data as well. In the study by Theuwissen and colleagues (2012), low doses of MK-7 improved vitamin K status in extrahepatic tissues but did not affect thrombin generation in healthy people. No systematic increase in thrombotic risk with dietary and moderate supplemental doses has been described.

A completely different situation is people who take vitamin K antagonist anticoagulants, primarily warfarin. For them, even relatively small doses of K2 can change the INR (international normalized ratio) and weaken the action of the medication. Schurgers and colleagues (2007) showed that MK-7 affects anticoagulation more strongly than K1 due to its longer half-life.

Therefore, the correct formulation is this: K2 does not "thicken" the blood of a healthy person but is a clinically significant factor for patients on warfarin. Direct oral anticoagulants (apixaban, rivaroxaban, etc.) act by a different mechanism, but any supplement against their background should also be coordinated with a doctor.

Myth 3: without K2 vitamin D is dangerous

On the internet there is a widespread claim that taking vitamin D without K2 inevitably leads to calcification of the vessels. It is based on the fact that vitamin D increases calcium absorption, while K2 helps "direct" it into the bones. Theoretically the combination makes sense, but the claim about the danger of D in normal doses is not confirmed.

Large randomized studies of vitamin D in moderate doses, conducted without adding K2, found no signal regarding an increase in cardiovascular events. The risk of hypercalcemia and calcification is real with toxic doses of vitamin D, but in that case the problem is solved by reducing the D dose, not by adding K2.

Clinical guidelines on vitamin D, in particular the recommendations of the Endocrine Society, do not require a mandatory combination with K2. Combined preparations are a convenience and a marketing niche, not a medical necessity for everyone.

At the same time, if a person has a low intake of foods rich in vitamin K, the combination can be a reasonable way to cover both needs. It is important to understand the difference between "may be useful" and "dangerous without it."

Myth 4: K2 is guaranteed to strengthen bones and prevent fractures

K2 activates osteocalcin — a bone tissue protein that binds calcium in the bone matrix. Therefore supplements are often advertised as a remedy against osteoporosis. The biochemical effect is real: studies, in particular by Inaba and colleagues (2015), showed that MK-7 reduces the share of undercarboxylated osteocalcin.

As for clinical endpoints, the picture is more modest. In the three-year study by Knapen et al. (2013), 180 µg of MK-7 per day slowed the loss of mineral density in individual areas of the skeleton in postmenopausal women, but the effect was moderate. The meta-analysis by Cockayne et al. (2006) showed a reduction in fracture frequency mainly in Japanese studies with MK-4 in pharmacological doses.

These Japanese works used doses of MK-4 of tens of milligrams per day, that is, hundreds of times larger than in ordinary MK-7 supplements. In addition, some of them had methodological limitations. Transferring their results to a capsule with 100 µg of MK-7 is incorrect.

For athletes and young people with healthy bones there are no data that K2 additionally increases skeletal strength. The foundation of bone health remains adequate intake of calcium and protein, normal vitamin D status, adequate energy availability, and strength training.

Myth 5: K2 is needed by everyone, and deficiency is widespread

Sellers often claim that the majority of the population has a K2 deficiency. The problem is that there is no separate official norm for K2: current recommendations concern vitamin K in general. Thus, the EFSA (2017) established an adequate intake of 70 µg per day for adults, while the American National Academy of Medicine — 90 µg for women and 120 µg for men.

Classic vitamin K deficiency, manifested by bleeding, is rare in adults. It occurs with impaired fat absorption, prolonged antibiotic therapy, liver diseases, or severe malnutrition. "Suboptimal" status in extrahepatic tissues, on the other hand, is assessed by markers such as dp-ucMGP, which are not yet routine tests.

The "triage" hypothesis (McCann, Ames, 2009) suggests that with a shortage of vitamin K the body primarily ensures blood clotting, while the bones and vessels receive the remainder. It explains why interest in extrahepatic effects is growing, but in itself it does not prove a need for a supplement for every person.

Thus, K2 may be appropriate for people with a diet poor in fermented products, certain osteoporosis risk groups, or on a doctor's recommendation. But the idea of "everyone taking it always" is not supported by evidence.

• Dietary sources of K2:natto (the richest source of MK-7), hard and soft cheeses, egg yolks, liver, some fermented products.
• Sources of K1:leafy green vegetables — spinach, kale, broccoli, lettuce.
• Groups where it is worth discussing status with a doctor:impaired fat absorption, prolonged antibiotic use, kidney disease, osteopenia.

Editorial conclusions

Vitamin K2 is a biologically important substance that activates osteocalcin and matrix Gla-protein. The mechanisms through which it affects bones and vessels are well described, and scientists' interest in it is entirely justified.

At the same time, the popular promises — cleaning of the vessels, guaranteed protection against fractures, obligatory status for everyone taking vitamin D — outpace the available evidence. The clinical effects, where they have been shown, are moderate and concern specific groups.

The true zone of caution is interaction with warfarin. For everyone else, K2 in normal doses is considered safe, but this does not mean that it is necessary.

We also recommend reading our materials "What to Combine Vitamin K2 With," a review of vitamin D for athletes, and an article on calcium and bone health.

References

1. Luo G, Ducy P, McKee MD, et al. Spontaneous calcification of arteries and cartilage in mice lacking matrix GLA protein. Nature. 1997;386(6620):78–81.
2. Geleijnse JM, Vermeer C, Grobbee DE, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100–3105.
3. Schurgers LJ, Teunissen KJ, Hamulyák K, et al. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007;109(8):3279–3283.
4. Knapen MH, Drummen NE, Smit E, et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int. 2013;24(9):2499–2507.
5. Knapen MH, Braam LA, Drummen NE, et al. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. Thromb Haemost. 2015;113(5):1135–1144.
6. Cockayne S, Adamson J, Lanham-New S, et al. Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Arch Intern Med. 2006;166(12):1256–1261.
7. McCann JC, Ames BN. Vitamin K, an example of triage theory: is micronutrient inadequacy linked to diseases of aging? Am J Clin Nutr. 2009;90(4):889–907.
8. EFSA Panel on Dietetic Products, Nutrition and Allergies. Dietary reference values for vitamin K. EFSA J. 2017;15(5):4780.