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Vitamin K2 and osteoporosis

Published 10.31.2016
I only learned about the existence of vitamin K2 about a year ago, when I poster in a discussion at the Carb-Sane Asylum claimed that he'd used vitamin K2 supplements in conjunction with vitamin D and calcium supplements to reverse his osteoporosis. That's a big claim, one that I was (and am) skeptical of. The amount of supplements he was swallowing daily was substantial, which does not appeal to me on any level.

However, despite my skepticism, I was intrigued, especially as I didn't even know what vitamin K was. What follows is the result of my efforts to research vitamin K, learn what foods contain it and wether or not it has any role in bone health. I admit that I began the study with an expectation that I was about to descend into a pit of "woo," but that did not turn out to be the case. In fact, the evidence on vitamin K2 and osteoporosis, while not definitive, is very interesting and suggestive.

Vitamin K isn't a single substance.

"Vitamin K," the generic name for a family of compounds with a common chemical structure of 2-methyl-1,4-naphthoquinone, is a fat-soluble vitamin that is naturally present in some foods and is available as a dietary supplement [1]. These compounds include phylloquinone (vitamin K1) and a series of menaquinones (vitamin K2) [2]. Menaquinones have unsaturated isoprenyl side chains and are designated as MK-4 through MK-13, based on the length of their side chain [1,2]. MK-4, MK-7, and MK-9 are the most well-studied menaquinones.

Phylloquinone is present primarily in green leafy vegetables and is the main dietary form of vitamin K [3]. Menaquinones, which are predominantly of bacterial origin, are present in modest amounts in various animal-based and fermented foods [1,4].


Vitamin K1 is abundant in green leafy vegetables, such as kale. Vitamin K2 is mostly found in animal products, with the exception of the Japanese fermented soybean dish called natto. In fact, natto hs the highest K2 content of any food. A healthy human body transforms K1 into forms of K2, which is why vegan doctors assert that if you eat plenty of green leafy vegetables, vitamin K2 levels should not be a problem. They seldom suggest that people eat natto, because not is an acquired taste for most people— even in Japan.

The MK-4 form of K2 is found in animal foods such as egg yolks, dairy products and beef liver. The form of vitamin K2 found in natto is MK-7. It also turned out that vitamin K2 has been studied as a way to increase bone strength. Both MK-4 and MK-7 have been studied, but a confounding factor is whether or not vitamin D and calcium were supplemented as well. It may well be that the internet commenter noted above is correct, and that it takes sufficient amounts of all three substances to affect bone health.

The authors noted the importance of considering the effect of vitamin D on bone health when comparing the results of vitamin K supplementation studies, especially if both vitamin K and vitamin D (and/or calcium) are administered to the treatment group but not the placebo group [37]. The administration of vitamin D and/or calcium along with vitamin K could partly explain why some studies have found that vitamin K supplementation improves bone health while others have not.


Vitamin K2 is used to treat osteoporosis in Japan (the MK-4 version), which is interesting to me because I've read that it's the observed difference in bone health between Japanese regions who eat natto (rich in the MK-7 form) that prompted the research into the K2 and osteoporosis. Europe also recognizes that K2 affects bone health, but the US does not.

In Japan and other parts of Asia, a pharmacological dose of MK-4 (45 mg) is used as a treatment for osteoporosis [5]. The European Food Safety Authority has approved a health claim for vitamin K, noting that "a cause and effect relationship has been established between the dietary intake of vitamin K and the maintenance of normal bone" [38]. The FDA has not authorized a health claim for vitamin K in the United States.


This link provides an excellent overview of Vitamin K2. It also provides a brief summation of K2 research, and I thought it well done. So well done in fact, that I'm not going to repeat their efforts, though that had been the original thought for this piece. Vitamin K is fat soluble, so the suggestion is to eat it will fat. Animal sources of K2 come replete with fat, as does natto for that matter. There are links to 15 studies specifically relating to bone mineral density (BMD), which it claims shows a moderate amount of consistency in results. BMD is the primary end point for studies of K2. There are other markers for bone activity, but the bottom line for treatment of osteoporosis is: is BMD increased? Some studies also look at bone breakage rates.

There appears to be a relative increase in bone mineral density associated with vitamin K supplementation, due to attenuating the rate of bone loss in older individuals. Although it is significant overall in meta-analyses, it is quite unreliable and similar in potency to vitamin D when it occurs (less than estrogen replacement therapy).


In addition to bone health, the effects of vitamin K2 on cardio-vascular disease has been investigated. The paper presents another good overview of vitamin K and its many forms, but I want to note there that I don't know what the International Health Foundation is or what it's bent is. Here is its quote about K2 and bone health.

Form definitely matters. In fact, studies on natto – a vitamin K2 rich traditional Japanese food based on fermented soy beans – support the importance of vitamin K2 in the form of menaquinone with seven iso- prene residues (MK-7). Kaneki and colleagues have showed that increased consumption of MK-7 leads to more activated osteocalcin, which is linked to increased bone matrix formation and bone mineral density, and therefore a lower risk of hip fracture.40


If this is correct, and MK-7 is the better form, then eating natto would be better than cheese and egg yolks (just about anything is better than liver…). The dosage for treatment is 180 micrograms (mcg), and it takes two years to see the effect on the bones.

Bottom line
This research convinced me that there is something to the idea that K2 has a positive effect on bone health. Because I am very much anti-supplements, I chose to ingest my K2 in the form of food, just as I do with calcium. Since natto is the highest food source of K2 on the planet, I began a search for a source of natto. I will discuss that further in the next installment. And simply for completeness, I will note that I am still taking a vitamin D supplement daily, despite my distaste for supplementation.

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