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Weak and easily broken fingernails. Calculus on the back of your lower front teeth. Osteoporosis. Atherosclerosis. What do these all have in common? Calcium. Either a lack of calcium where you do want it or calcium where you don’t want it. What does vitamin K2 have to do with all this?  K2 is an essential cog in the body’s machinery to transport calcium to where it is needed.  Without enough of it, the calcium ball gets dropped in undesirable places and never gets to where it belongs.

K2 is found in microscopic quantities in beef and dairy from cattle fed on fresh grass,  eggs, and the fermented soybean product known as natto.  It is lacking in the modern diet, and you won’t find it in most multivitamins either.  However, it is available cheaply as a separate supplement.  Join me over the fold for more detail.
 

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What follows next is geeky stuff; if you find this boring just skip down to the MK-4 vs. MK-7 section.

Vitamin K2 is essential in the synthesis of two different proteins that are in turn essential for calcium transport, Matrix gla protein (MGP)  and Osteocalcin.

MGP:

This calcification inhibitory protein is found in numerous body tissues, but its role is most pronounced in cartilage and in arterial vessel walls.  Mice that lack MGP develop to term but die within two months as a result of arterial calcification which leads to blood-vessel rupture.  
Osteocalcin:
is found in bone and dentin. Osteocalcin is secreted solely by osteoblasts and is pro-osteoblastic, or bone-building, by nature.
Lack of osteocalcin may play a role in type 2 diabetes:
mice lacking the osteoblast-secreted molecule osteocalcin display decreased β-cell proliferation, glucose intolerance and insulin resistance.
Clinical evidence:
Bone density
It has been found that vitamin K deficiency results in a decreased level of active osteocalcin, which in turn increases the risk for fragile bones.[2][3] Research also showed that vitamin K2, but not K1 in combination with calcium and vitamin D can decrease bone turnover.[4] Moreover, a study performed by Knapen et al. clearly demonstrated that vitamin K2 is essential for the maintenance of bone strength in postmenopausal women, and was the factor for improving bone mineral content and femoral neck width.[5]

More arguments supporting the unique function of vitamin K2 came from Japan. The Japanese population seems to be at lower risk for bone fractures compared to European and American citizens. This finding would be paradoxical, if levels of calcium consumption were the only factor determining bone density. However, Japanese studies published in 2006 and 2008 link Japan's greater levels of BMD to that country's widespread consumption of natto, a traditional breakfast dish made of fermented soybeans. Increased intake of MK-7 from natto seems to result in higher levels of activated osteocalcin and a significant reduction in fracture risk.[6][7]
Even more striking is the research finding, reported in 2001, that there seems to be an inverse correlation between the amount of natto consumed, in different regions of Japan, and the number of hip fractures. In regions of the country where natto is not part of the daily diet, hip fractures are more common.[8]

Heart calcification
Patients suffering from osteoporosis were shown to have extensive calcium plaques, which impaired blood flow in the arteries. This simultaneous excess of calcium in one part of the body (arteries), and lack in another (bones) –which may occur even in spite of calcium supplementation - is known as the Calcium Paradox. The underlying reason is vitamin K2 deficiency, which leads to significant impairment in biological function of MGP, the most potent inhibitor of vascular calcification presently known. Fortunately, animal research showed that vascular calcification might not only be prevented, but even reversed by increasing the daily intake of vitamin K2.[9] ]

K1, K2, and MK-4 vs. MK-7

Vitamins K1 and K2 are not interchangeable.  Although they are quite similar in structure, K1 is essential for producing clotting factors but cannot be used by the body in place of K2.  In the structures shown below, Mk-4 and MK-7 are variants of K2

Interestingly, the only difference between K1 and the MK-4 version of K2 are double bonds in the “tail”.  There is some disagreement over whether MK-4 or MK-7 is better.  The author of this book (apparently out of print for the moment and for sale for an exorbitant price) believes Mk-7 is best because it has a longer plasma half-life.  Some reviewers of this book, on the linked page, believe MK-4 is better.  Based on personal experience detailed below, I believe MK-7 is more effective.  Most supplements have some of each which I think is best.

Personal Experience

After starting K2, many people, myself included, experience a reduction or even complete disappearance of the calculus that accumulates on the backs of the lower front teeth.  I am due in a few weeks for my regular dental hygiene appointment.  Usually by now there is plenty of calculus to scrape off, but there is none now.

But even more important was  my fingernails had gotten into the bad habit of breaking.
Little bites suddenly missing. I am quite sure it was not some little creature in the middle of the night! It was really distressing because it was happening all by itself without having broken them on anything. On the corners, in the middle, and overall weak and fragile.  A few weeks after starting K2 they were pretty much back to their usual selves.  I have been taking MK-4 and MK-7 separately.  I ran out of the MK-7 for a few weeks and they started to get fragile again.  So that is my evidence in favor of MK-7.

One other personal observation. All my life I have worn size 9 1/2 - 10 1/2 shoe.  After many decades of adulthood, after 6 months of K2, my feet  have grown from size 10 1/2 to size 12, in the same make and model shoe.  Growing out of one's shoes counts as a downside, but a small price to pay for a healthy skeleton!

What to get

If you look on your multivitamin ingredients and see “Vitamin K as phytonadione” or some such, that is K1.  K2 is known as menaquinone.  The MK-7 supplements I have seen only have 100 micrograms (usually listed as “mcg”), but that seems to be enough.  You can get MK-4 only supplements with much higher amounts but more is not necessarily better.  Best to get a supplement with some of each.  No maximum dose upper limit has been reported.  Available from Vitacost, Swanson’s etc.

If you don’t like supplements, unless you eat a lot of meat and cheese, the best source of K2 (MK-7) is natto.  Natto is fermented soybeans in a gel matrix with a mucus-like consistency.  It tastes like very strong coffee, and for that reason it did not work for me.  One teaspoon will get you 100 micrograms of MK-7. Available here.

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