The Unassuming, Yet Essential, Vitamin K

Vitamin K consists of a group of vitamins that support blood clotting, bone metabolism and also help to regulate blood calcium levels. What may not be so obvious about vitamin K is its ability to maintain a person’s mobility. Vitamin K levels are key not only for your bones and joints but also for your cardiovascular health^1,2. 

Discovery of Vitamin K 

Vitamin K was first discovered in 1935, when it was found to be an essential nutrient to prevent abnormal bleeding in chickens³. For decades thereafter, vitamin K was identified as the “coagulation vitamin” (in fact, the initial “K” comes from the German spelling, koagulation). Vitamin K activates specific proteins made in the liver that are required for normal blood clotting. The vitamin K antagonist Warfarin (a blood thinner) is effective at reducing clotting due to its antagonistic to the effects of vitamin K. Without sufficient vitamin K, blood would not clot, and severe bleeding would ensue^4,5. But the vitamin Ks play more roles than just blood clotting. The body normally tears down and builds bone all the time. Building bone requires osteocalcin, which binds tightly to bone minerals to create strong bones. And sufficient vitamins K1 and K2 are required to activate that osteocalcin⁶.  

Vitamin K and Osteocalcin

Osteocalcin is one of a family of Gla-proteins. Vitamin K activates the Gla proteins (including key proteins in blood clotting) by making a small but vital chemical change in the proteins’ structure, specifically on the protein building block called glutamic acid⁷. Once thought to be exclusively concerned with blood coagulation, vitamin K is now known to affect at least 16 Gla-proteins in the body. These include proteins involved in strengthening bones and supporting artery health, which suggests the health importance to getting sufficient vitamin K. 

Calcium reinforcement in bones is positive as it makes the bones less likely to break; however, calcium in the arteries (not just in plaques but in the walls or normal appearing arteries) may cause stiffening and could increase blood pressure. The goal is to help move calcium from blood to the bone, and natural vitamin K can help support this process. 

Vitamin K Research

The current scientific landscape around vitamin K supports its health benefits, but do not prove by themselves that getting enough Ks is important. A study of healthy postmenopausal women who took 1 mg/day of vitamin K1, plus 8 micrograms (320 IU)/day of vitamin D together with minerals, reduced the loss of bone in the hip and spine compared both to placebo recipients and to those supplemented with vitamin D and minerals alone⁸.  

In another study, postmenopausal women with pre-existing osteoporosis took 1,500 mg of calcium carbonate and 45 mg of vitamin K2 or placebo each day for 48 weeks. The women who took the K supplement increased spinal bone mineral density while a 9.3 percent reduction occurred in the group taking only the calcium supplement⁹. The same level of K2 was later shown to maintain hip bone strength and support the overall geometry of the femoral neck over a three-year period, while placebo recipients lost hip bone strength during that time¹⁰. Even lower levels of 180 micrograms/day of vitamin K2 when given for three years, significantly supported bone mineral content and density in the lower spine and femoral neck, while also increasing bone strength¹¹.

Emerging Research

Vitamin K also appears to impact glucose levels¹². And in a study of older adults at high risk for cardiovascular disease, the risk of developing type II diabetes was reduced by 17 percent per 100 micrograms of K1 intake per day¹³. In addition, individuals with the highest vitamin K1 intakes have shown reductions in inflammatory markers related to diabetes¹⁴. This increased insulin sensitivity and reduction in inflammation may be a result of increases in the vitamin K-dependent Gla-protein osteocalcin, which has been shown in pre-clinical studies to increase insulin secretion and sensitivity¹⁵.

Sources of Vitamin K

Eating vitamin K-containing vegetables at the same time as fat, may support its absorption¹⁶. Of the foods I love, sources of vitamin K1 include leafy greens like kale and spinach. All of us can seek out healthy sources of fat to pair them with such as plant oils like olive and avocado. Unlike other fat-soluble vitamins, vitamin K circulates in very small amounts in the blood before it is rapidly metabolized and excreted –that is a reason to make sure you get vitamin K in a supplement as well^16,17. A relative of coenzyme Q10, vitamin K2 can be found in chicken and in something called Kefir, a foamy, creamy milk-like drink. So does natto—a Japanese fermented soybean dish. Fun fact – Samurai warriors would eat natto to increase their strength and quicken their reflexes. Seek out foods and supplements with vitamin K1 and K2 to support your both strength and mobility. 

Michael Roizen, M.D. is the author of the book “AgeProof: Living longer without breaking a hit or running out of money.” 

Follow NUTRI-FACTS on Facebook @Understanding.vitamins to stay updated on the latest nutrition news and expert commentary. 

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