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Thoughts at Large: Controversies in Clinical Nutrition and Functional Medicine Issue # 12 VITAMIN K1 VERSUS THE MK-7 VERSION OF VITAMIN K2 SUPPLEMENTATION: WHICH IS BEST FOR YOUR PATIENTS?


It is now well recognized in the clinical nutrition community that vitamin K supplementation can be a valuable adjunct to vitamin D supplementation when optimization of bone health is a patient priority. Why? In simple terms, optimal vitamin K levels assure that the impact of vitamin D in terms of calcification will be primarily directed towards bone and not soft tissues. However, there is confusion in terms of what is the best form of vitamin K supplementation in this regard.

Because of this confusion about the different forms of supplemental vitamin K and which is best for your patient, this commentary will be devoted to a review of the paper "Vitamin K-containing dietary supplements: comparison of synthetic vitamin (K.sub.1) and natto-derived menaquinone-7" by Schurgers et al (Schurgers LJ et al. Hemostasis, Thrombosis, and Vascular Biology, Vol. 109, No. 8, pp. 3279-3283, April 2007), which provides an excellent explanation of the most popular forms of supplemental vitamin K but a rationale as to why the MK-7 form of vitamin K may be best.



Schurgers et al begin their paper by discussing basic vitamin K biochemistry and physiology:

"Vitamin K is a group name for a number of structurally related compounds including phylloquinone (vitamin (K.sub.1) and menaquinones ([K.sub.2] vitamins). Menaquinones are classified according to the length of their aliphatic side chain and are designated as MK-n, where n stands for the number of isoprenoid residues in that chain."

As will be discussed in more detail, the commercially available forms of vitamin [K.sub.2] menaquinones are MK-4 and MK-7. As will also be discussed, there are distinct benefits to the MK-7 form. The authors continue with their discussion of vitamin K biochemistry and physiology:

"The function of all forms of vitamin K is that they serve as a cofactor for the posttranslational carboxylation of certain protein-bound glutamate residues, which are converted into gamma-carboxy glutamate (Gla). These Gla residues from calcium-binding sites that are essential for the activity of the proteins in which they are found."

What does this mean in plain English? There are certain glutamate residues that are important for directing calcium where it is needed the most. These glutamate residues, though, cannot perform their functions unless a carboxyl group is added to them. Vitamin K facilitates addition of the carboxyl group to the glutamate residues so these residues can do their job in terms of calcium metabolism.

The next important clinical point made by Schurgers et al relates to the metabolic fate of vitamin K: "During gamma-glutamate carboxylation, vitamin K is oxidized into its epoxide form (KO), which is reconverted to vitamin K quinone (K) by the enzyme vitamin K epoxide reductase (VKOR)."

What does this mean in plain English? During the process of donating the carboxyl group, vitamin K is oxidized to an inactive form. The enzyme VKOR converts oxidized vitamin K back to an active vitamin K form, thus conserving vitamin K. Why is it important clinically to know this? Blood-thinners such as warfarin inhibit VKOR, thus preventing oxidized vitamin K from being recycled:

"Derivatives of 4-hydroxycoumarin (including warfarin and acenocoumarol) specifically inhibit VKOR, thus preventing the recycling of vitamin K."

In what organ systems do Gla-containing proteins play a role in terms of facilitating optimal calcium metabolism? One important area, as we know, is blood clotting:

"Well-known Gla-containing proteins are the blood coagulation factors II, VII, IX, and X, which are all synthesized in the liver."

However, still other Gla-containing proteins facilitate optimal calcium metabolism in tissues outside of the liver:

"Gla-proteins not related with blood clotting are osteocalcin (synthesized in bone) and matrix Gla protein (primarily synthesized in cartilage and in the vessel wall."

Thus, as the above quote suggests, Gla proteins that need vitamin K for proper formation also are essential for proper calcium metabolism in bone, cartilage, blood vessel walls.


Schurgers et al state the following about food sources of the various forms of vitamin K:

"In food, the most important K vitamins are [K.sub.1] (notably found in green vegetables and some plant oils) and the long-chain menaquinones MK-7, MK-8, and MK-9 present in fermented foods, notably cheese and natto."

Before continuing, please note that the most well-known source of vitamin K, green vegetables, only provides vitamin [K.sub.1]. Green vegetables are not a source of vitamin [K.sub.2]. The clinical importance of this distinction will be discussed later in this monograph.

The next quote from the Schurgers et al paper discusses supplemental forms of vitamin K:

"In food supplements, 3 forms of vitamin K may be found: MK-4 (prepared by organic synthesis and almost exclusively used in Japan), [K.sub.1] (also synthetic and the predominant form used in the rest of the world), and MK-7 (a natural form prepared by extraction of natto food)."

Interestingly, the structures of [K.sub.1] and MK-4 are very similar:

Since the molecular structures of [K.sub.1] and MK-4 are comparable..., their physico-chemical characteristics are closely similar."

In contrast, MK-7 is unique:

"The higher menaquinones including MK-7 are much more hydrophobic, however, and in vivo they are handled very differently: they have longer half-life times, and in the circulation, they are incorporated into low-density lipoproteins."

Of course, [K.sub.1] is the most well-known of the three, having been available for years. However, MK-7 is continuing to attract increasing interest: "[K.sub.1] is by far the most common form of vitamin K in commercially available supplements, but because of the health claims for the regular consumption of natto that are repeatedly made in the scientific literature, MK-7 in the form of a natto extract is rapidly gaining interest."


The remainder of the Shurgers et al paper discusses research that compares clinical benefit of MK-7 versus [K.sub.1]. Probably the biggest clinical benefit, as noted in the quote below, is that MK-7 performs much better than [K.sub.1] in terms of promoting bone health.

However, as you will also see, it is more effective in promoting clot factors in the liver making it more effective in reducing the effectiveness of coumarin anticoagulants:

"In this paper we have compared the in vivo properties of 2 forms of vitamin K: MK-7 and [K.sub.1]. We demonstrate that after oral ingestion, MK-7 is more effective in both catalyzing osteocalcin carboxylation in bone and counteracting coumarin anticoagulants in the liver.

The mechanism underlying this observation may be MK-7's much longer half-life time in the circulation and its reported 6-fold higher cofactor activity in vitro." However, before continuing, as will be reported shortly, the adverse impact of MK-7 on efficacy of coumarin anticoagulants is dose-dependent.

The next quote discusses more reasons why MK-7 performed better than [K.sub.1]. As you will see, the main reason is what was mentioned above - MK-7, unlike [K.sub.1], can be taken up and circulated via low-density lipoproteins: "The difference between the 2 vitamins may be related to the fact that following intestinal absorption, both are taken up in the triglyceride fraction from which they are rapidly cleared by the liver but that only higher menaquinones are redistributed via low-density lipoproteins.

A consequence of the long half-life time of MK-7 is that it is available longer than [K.sub.1] for uptake by extrahepatic tissues. If expressed as area under the curve (AUC) over 24 hours, the availability of MK-7 is 2.5-fold better than that of K:; if expressed as AUC over 96 hours, it is even 6-fold better."

What does this mean in terms of dosing? The authors comment:

"This means that if taken in single daily doses of 100 ug, only MK-7 is effectively present in the circulation and available for absorption by various tissues during the 24 hours following intake."

The authors continue:

"...if taken on a regular basis, there is no accumulation of [K.sub.1], whereas MK-7 accumulates...during the first 2 weeks, after which a steady-state level is reached. At comparable intakes, the final level of MK-7 was 7- to 8-fold higher than that of [K.sub.1], suggesting that if taken on a daily basis, 25 [micro]g/d of MK-7 is more efficacious than 100 [micro]g/d of [K.sub.1]"


On the positive side, it appears that because, in many adults, there exists a fair amount of undercarboxylated osteocalcin (ucOC), which will not be optimally effective in promoting bone health, MK-7 will be much more effective in repleting what appears to be a very common state of vitamin K deficiency in bone:

"In the healthy adult population, about 30% of the circulating osteocalcin occurs in its undercarboxylated form, and increased vitamin K intake results in rapid decline of ucOC, suggesting a state of subclinical vitamin K deficiency in healthy bone tissue.

In a study designed to compare the efficacy of equimolar amounts of [K.sub.1] and MK-7, we measured the degree of osteocalcin carboxylation after a 6-week period of vitamin K intake. A small increase of osteocalcin carboxylation was visible for both forms of vitamin K at day 3, but whereas the effect of [K.sub.1], remained constant after that time, that of MK-7 inclined during the entire 6 weeks of treatment. At the end of the study, the change in the carboxylated OC/undercarboxylated OC ratio was 3 times higher for MK-7 than for [K.sub.1], suggesting that the higher serum levels of MK-7 reflect higher tissue levels and better utilization of MK-7."

Of course, on the negative side, this increased tissue utilization of MK-7 can pose problems for patients using coumarin anticoagulants. One reason is that, unlike osteocalcin in bone, in the average healthy population clotting factors in the liver are fully carboxylated: "The vitamin K-dependent clotting factors are all produced in the liver and, in contrast to osteocalcin, they are all fully carboxylated in the healthy population."

What does this mean clinically in terms of anticoagulant medication? The authors state:

"It turned out that if expressed on a molar basis, MK-7 is a 3 to 4 times more potent antidote for oral anticoagulation than is [K.sub.1]. If expressed per weight, the efficacy of MK-7 in the liver is still 2.5 times higher than that of [K.sub.1]."

What does this mean in terms of a dose of vitamin K that will not interfere with coumarin activity?

"In a previous paper we demonstrated that vitamin [K.sub.1] supplements containing no more than 100 [micro]g/d are not likely to result in clinically relevant disturbances of oral anticoagulant therapy. Extrapolating these figures, it may be concluded that MK-7 supplements containing more than 50 ug/d may interfere with oral anticoagulant treatment, whereas doses of at least 50 ug are not likely to affect INR value in a relevant way."


The first statement is a summary of the different properties of [K.sub.1] versus MK-7 and why MK-7 would be a preferable supplement:

"Taken together, these data demonstrate considerable differences between MK-7 and [K.sub.1],: higher and more stable serum levels are reached with MK-7, and MK-7 has a higher efficacy in both hepatic and extrahepatic protein carboxylation. During recent years many studies have demonstrated that the extrahepatic vitamin K requirement exceeds the recommended daily allowance (100-120 [micro]g/d) for vitamin [K.sub.1]. For the food industry, an alternative to increasing the recommended dose would be introducing on a larger scale the more potent MK-7 instead of [K.sub.1], in functional foods and multivitamin supplements."

Of course, as was mentioned, the downside of MK-7 supplementation relates to its impact on anticoagulant therapy:

"Hematologists, on the other hand, need to be aware that relatively low doses of MK-7 may have a larger impact on the stability of oral anticoagulation than vitamin [K.sub.1]."

With the above in mind, Shurgers et al make the following recommendation:

".. .we propose to use an upper safety limit for intake of 50 [micro]g/d for long-chain menaquinones (including MK7) in patients on oral anticoagulant treatment. This dose is comparable with the menaquinone content of 75 to 100 g of cheese; such an amount would lead to a disturbance of the INR value of no more than 10% which may be regarded as tolerable in the management of oral anticoagulant therapy."

Shurgers et al end their paper on a positive note in relation with the use of MK-7 with patients on anticoagulant medication:

"...its long half-life time suggests that regular intake of MK-7 in combination with properly adapted coumarin doses may result in more stable INR values."


Despite all the emphasis on vitamin D supplementation as an aid to the optimization of bone health, there is, in my opinion, a significant lack of emphasis on the need for optimal vitamin K levels to assure that vitamin D supplementation fulfills its primary intent for the osteopenic/osteoporotic patient, the optimization of bone health.

Unfortunately, due to the availability of different forms of vitamin K supplementation on the market along with the somewhat complicated interactions with the commonly prescribed drug, warfarin, there exists some confusion on how the nutritional practitioner should proceed in terms of making recommendations to patients about vitamin K supplementation.

Hopefully, this review and commentary of the Schurgers et al paper will add some much-needed clarity to the subject.

by: Jeffrey Moss, DDS, CNS, DACBN.
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Author:Moss, Jeffrey
Publication:Original Internist
Article Type:Report
Geographic Code:1USA
Date:Jun 1, 2019
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