Vitamin K is comprised of two different compounds in the body. K1 is responsible primarily for the coagulation of the blood while K2 is responsible for calcium metabolism within the body and cardiovascular health. K2 was only recently identified in foods in 2006 by the FDA after studies concluded its benefit to the human body. Most of the vitamin K obtained from diet is the K1 variety --. it is somewhat harder to find foods that supply vitamin K2.
Natto
The best source of food with the highest amount of K2 is natto. Natto develops from fermented soybean. When soybeans ferment, they develop into a mass that has a stringy, phlegm-like consistency. It smells vaguely like ammonia, and is an acquired taste. Natto is a traditional Japanese food and contains vitamin K2, in its three different structural forms, in quantities of approximately 1000 mg per 3.5 oz. serving. The three different forms have differing residence times in the body, and absorb from the digestive tract to different degrees.
Aged or Fermented Cheese
Fermented cheese, such as blue or feta, contains moderate levels of vitamin K2. Other hard cheeses that have been aged, such as cheddar, contain a high amounts as well, with the softer cheeses only slightly less.
European Prospective Investigation into Cancer and Nutrition reported on a study which indicated that vitamin K2 was a benefit to patients suffering in the advanced stages of prostrate cancer. Vitamin K1 studies have resulted in no observable benefit. This may further indicate that the two types of Vitamin K operate in the body differently and affect different systems.
Eggs and Meats
K2 can be found in meats such as chicken and beef, and particularly in the livers of these animals. K2 is also present in salami, and the organ meats and fats of animals. Previously it was thought that the human digestive tract contained bacteria that synthesized K2 from the K1 present in the body, however most current research indicates that the K2 generated in this manner does not readily absorb into the body.
Vegetables
K1 is easier to obtain through the diet when you consume green leafy vegetables, such as Swiss chard, collard greens, spinach and kale. Other than the sources listed in this article, most sour, fermented foods like sauerkraut and kefir also contain some vitamin K2.
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