Vitamin K: Neglected Nutrient?

by Christine Carlson, CN, NEEDS Wellness Educator

Thinning bones, hardened arteries: what do these two degenerative health conditions have in common? It turns out that an insufficiency of a simple nutrient, vitamin K, may be a key to reversing both conditions.

"Research has shown poor vitamin K intake may be associated with conditions such as bone fractures, bone loss, hardening of the arteries, and osteoarthritis," says Sarah Booth, who is a vitamin K researcher and professor at Tufts University.

Why haven't we heard more about this nutrient?

Conventional thinking has taught us three erroneous concepts:

1) We get plenty of vitamin K from food.

2) We only need it for proper blood coagulation.

3) It can be toxic.

Thus it has rarely been included in multi-vitamin-mineral formulas.

Vitamin K is available in our diet in two basic forms: K1 (phylloquinone); and K2 (menaquinones), of which there are several subtypes, most importantly MK-4 and MK-7. Vitamin K1 is found in the green tissues of plants and it appears that humans have a limited ability to absorb K1, although that rate is normally adequate. K2, which is very different than K1, can be converted from K1 by bacteria in the large intestine. Vitamin K deficiency has been considered uncommon unless the intestines are heavily damaged, or are unable to absorb it due to decreased production by normal flora, as seen in broad spectrum antibiotic use. Unfortunately, this describes the state of intestinal health of many individuals today, thus requiring supplementation. And, even though the intestinal conversion was once thought to be a major source of K in human nutrition, it appears from current research that most vitamin K2 produced in the intestine is embedded within bacterial membranes and is not available for absorption. However, vitamin K2 is found in meat, fish, and eggs, and is also produced by lactic acid bacteria found in fermented foods such as sauerkraut, cheese, and natto. These appear to be useful food sources of K2 for humans.

Historically, researchers have tended to dismiss the contribution of K2 since K1 is much more abundant in typical diets. But recently an increasing amount of research is demonstrating that these two substances have different and equally important functions in the body.

While K1 is preferentially used by the liver to activate blood clotting proteins, K2 has other functions. Primarily, it has been recognized for its beneficial effect on building bones. Without enough vitamin K2, calcium can not be utilized for bones, leading to osteoporosis.

But, here's the important part for heart health: connected with the softening of bones is hardening of arteries. Vitamin K2 is crucial for moving calcium into the bones instead of letting it deposit in arterial walls.

It does this through a process called "carboxylation". This gives certain protein molecules "claws" to grab onto calcium so it can be transported. If there is not enough vitamin K2, these proteins will be "undercarboxylated" and can't control the calcium, which then can drift from bone and into arteries and other tissue, contributing to atherosclerotic and soft tissue calcifications. Human studies have shown that K2 is associated with a lower risk of coronary calcification, and in animal studies vitamin K has reversed arterial calcification. In addition to reducing or reversing arterial calcifications, K2 appears to have additional benefits for the cardiovascular system in that it helps protect against inflammation and accumulation of lipids and white bloods cells that are signatures of atherosclerosis.

In addition to all the benefits for bones and cardiovascular health, it appears that vitamin K may help improve insulin sensitivity, kidney function, and digestion. For example, in animal studies, researchers found that vitamin K deficient animals developed type II diabetes. And regarding kidney function, it has been observed that vitamin K-dependent proteins inhibit the growth of calcium oxalate crystals, one cause of kidney stones.

Some signs of possible vitamin K deficiency include bruising, malabsorption, and unusual bleeding (gastrointestinal bleeding, excessive menstrual bleeding, blood in the urine, and nosebleeds). There appear to be many intracellular functions of K2 that are presently only poorly understood and as research progresses, new functions for this vitamin will undoubtedly emerge.

Many people have been afraid that vitamin K is dangerous to supplement, since it is a fat-soluble vitamin. However, just as we have found with vitamin D, higher supplemental doses are not toxic. Vitamin K is not stored in the body. In addition, people have worried that if you take supplemental K, your blood might clot too much, but this is not true. High amounts of vitamin K1 will not cause your blood to overcoagulate. Coagulation proteins only have a certain number of spaces for vitamin K. Once those spaces are filled, vitamin K cannot affect coagulation proteins. And no toxicity has been shown with current supplemental doses of K2. Dosing generally ranges from 100 mcg to 4,000 mcg combined K1 and K2. The only toxicity well-documented is with K3, a synthetic form. The only other warning is for those on blood thinners (anticoagulants) such as coumadin, who must consult their doctor before using vitamin K. But because anticoagulants can cause arterial calcifications through the inhibition of vitamin K, some research is suggesting that individuals who discontinue anticoagulant therapy should consider supplementing with K2.

With this ongoing, exciting research, we have a new perspective on vitamin K, especially K2. It may be a missing piece in many nutrient protocols, and can be safely added to most individuals' supplementation plans for better long-term optimal health.