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Every vitamin is vital to some function of human metabolism. Vitamin K2 is often overlooked, but it is vital to building healthy bones.

If you have osteoporosis, you need vitamin K2. Whether you get your K2 from supplements or you dine on Irish butter, French cheeses, Japanese natto, and farm-fresh eggs with bright orange yolks, vitamin K2 can strengthen your bones and help you avoid osteoporosis.

What is vitamin K2?

Vitamin K was discovered about 90 years ago by a Danish chemist who reported his findings in a German journal that labeled it the "Koagulationsvitamine" because it played a role in blood clotting. The chemical the chemist discovered became known as vitamin K. Although vitamin K is definitely important in the clotting process for human blood, it's more useful to think of it in terms of its role in regulating calcium. One form of vitamin K, vitamin K1, regulates calcium in blood clotting. Another form of the vitamin, vitamin K2, ensures that calcium gets into the tissues where it is needed (for example, bones) and stays out of tissues where it is not (for example, the linings of the arteries). It turns out that K2 plays an important role in preventing osteoporosis.

How to you get your K? People who eat their greens get plenty of vitamin K1 , which is especially abundant in leafy vegetables. Very few people really need a vitamin K1 supplement. Vitamin K2, in contrast, is synthesized by bacteria in the gut. We get our K2 by eating foods from animals that have these bacteria in their digestive tracts, such as diary products from grass-fed cows and eggs from grass-fed chickens. There is also a vegan food called natto that provides K2. The chemical name for vitamin K2 is menaquinone. You may see this chemical term on the labels of vitamin K supplements that are helpful in maintaining bone health. Menatetrenone is the brand name of a synthetic form of vitamin K2 that is chemically identical to menaquinone. The K1 form of the vitamin, phylloquinone, which is abundant in leafy greens, isn't the form of the vitamin you need for bones.

What does vitamin K2 do for bones?

Vitamin K2 activates a protein that helps bones metabolize calcium called osteocalcin. K2 acts as a coenzyme to activate osteocalcin to "glue" itself to the bone mineral hydroxyapatite in bone-building cells called osteoblasts. This ensures that bone builds itself on a protein scaffold that keeps it strong but flexible.

How much vitamin K2 do we need?

Deficiency symptoms set in when people get less than 250 to 300 micrograms of vitamin K2 per day. Clinical studies in Japan have found that the optimum dose of K2 for bone growth, not too low, not too high, is 45 milligrams of K2 per day. That is 150 to 180 times the recommended daily intake to prevent bone problems. In most countries you will get 45 milligrams per dose in a K2 supplement. HealthCanada, however, restricts the amount of K2 in a supplement to 300 micrograms, which is not really enough to do any good.

What is the proof that vitamin K2 works?

Vitamin K2 has been extensively studied in clinical trials in Japan. Here is what the studies found:

  • In one clinical trial, Japanese researchers gave women 45 mg of K2 per day or no other treatment at all for two years. In this study, K2 reduced bone mineral loss in the spine to an average of 0.5 percent, while women who got no treatment at all had spinal bone mineral loss averaging 3.0 percent. K2 by itself helps but does not stop osteoporosis.
  • In another clinical trial, Japanese researchers gave women just K2, just calcium, or both K2 and calcium for two years. The women who got both Kand calcium had improved bone mineral content in the spine at the end of the study. The women who got only calcium lost bone minerals in the spine.
  • In a third study in Japan involving women who had already been diagnosed with osteoporosis, the researchers gave either calcium plus K2 or a placebo. The women who got both calcium and K2 had improved bone mineral content of the spine at the end of two years. The women who got the placebo had weaker spines at the end of the two years.
  • And in a series of studies, taking K2 decreased the risk of fractures even when it did not increase the mineral content of bone.

(These studies used the synthetic form of vitamin K2 known as menatetrenone.)

These studies and about a dozen more give strong clinical evidence that getting an optimal amount of vitamin K2 enhances bone strength and prevents fractures post-menopausal osteoporosis. The best source of vitamin K2 is a Japanese fermented soy food called natto. It's slimy and smells like dirty tennis shoes, and it is hard to find except in Japanese and Korean groceries. Butter made from cream from milk from grass-fed cows and brightly colored egg yolks are also a good source of K2. But it easiest to get your K2 from supplements.

Bacteria in your colon can convert the vitamin K1 you get from salads and leafy greens into vitamin K2. If you aren't on an anticoagulant like warfarin (Coumadin), it is a good idea to eat your greens every day for bone health. The amount of K2 you indirectly obtain from plant foods, however, is not enough to promote bone health. K2 supplements are best.

  • Iwamoto J. Vitamin K₂ therapy for postmenopausal osteoporosis. Nutrients. 2014 May
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  • Iwamoto J., Takeda T., Ichimura S. Effect of menatetrenone on bone mineral density and incidence of vertebral fractures in postmenopausal women with osteoporosis: A comparison with the effect of etidronate. J. Orthop. Sci. 2001. 6:487–492. doi: 10.1007/s007760100002..
  • Orimo H., Fujita T., Onomura T., Inoue T., Kushida K., Shiraki M. Clinical evaluation of soft capsule menatetrenone (Ea-0167) in the treatment of osteoporosis. Late Phase II Dose Study. J. New Rem. Clin. 1992.41:1249–1279. (in Japanese).
  • Photo courtesy of SteadyHealth

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