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Why You Might Need Vitamin K

Why You Need (and Might Need) Vitamin K

 Of the 13 vitamins essential for human health, vitamin K is among the least familiar to most people. But that may change as researchers report new findings about the vitamin's key roles in the body, especially for bone health.


Like vitamin E, vitamin K is actually a group of structurally similar fat-soluble vitamins. It is necessary for the production of proteins needed for the coagulation of blood and other functions, and it works synergistically with vitamin D for bone health and possibly cardiovascular health. The K comes from Koagulation, German for coagulation, meaning the ability of blood to clot and thus prevent hemorrhage.

Getting to know K

There are two main types of the vitamin:

Vitamin K1 (phylloquinone). Well known for its role in blood clotting, K1 is found in many plant foods, notably leafy greens, such as spinach, kale, and collards, as well as broccoli, Brussels sprouts, cabbage, and other cruciferous vegetables. Consuming some fat with these foods improves absorption of vitamin K. Smaller amounts are found in soybeans, avocados, asparagus, kiwifruit, and a few vegetable oils (notably soybean and canola). The synthetic form of K1 used for medical injections and in many supplements is called phytonadione.

Vitamin K2 (menaquinones, designated as MK-1 to MK-13, depending on the length of their molecular structure). Important for calcium regulation in bones, cartilage, and blood vessels, K2 has been getting increasing attention from researchers. It is synthesized by bacteria, including various types in the intestinal tract. Moderate amounts are found in animal foods, such as dairy, chicken, egg yolks, and meat. Certain types of K2 (notably MK-7) are found in fermented foods such as cheese and particularly natto (a fermented soy product); the types and amounts of K2 depend on the bacterial strains used to make the foods and the fermentation conditions. Since vitamin K is fat-soluble, full-fat dairy products (such as milk, yogurt, cheese, and cottage cheese) contain much more K than reduced-fat ones; nonfat dairy products contain little or no K.

Vitamin K2 accounts for about 10 to 25 percent of average vitamin K intake, coming mostly from dairy in Western countries. Intestinal bacteria make some vitamin K2, but it's unclear how much of this can be utilized by the body.