Vitamin K is a fat soluble vitamin found primarily in leafy green vegetables. It is required for the synthesis of proteins involved in homeostasis(blood clotting) and with bone metabolism. Vitamin K is present in the liver, brain, heart, pancreas as well as in the bones. The body retains little Vitamin K as it is metabolized much more quickly than other fat soluble vitamins.
Major food sources of Vitamin K include vegetables, vegetable oils and some fruits. Foods with the highest concentration of Vitamin K are collard greens, turnip greens, spinach, kale, broccoli, carrot juice, soybeans, pomegranate juice and pine nuts. Most U.S. diets contain sufficient Vitamin K, it is also widely available in supplement form.
Vitamin K deficiency is very rare in adults, it is found most often in people with malabsorption disorders. It can also be found in people who have received gastric bypass surgery. Infants who don’t receive Vitamin K supplementation are also at risk of deficiency as there is little Vitamin K in breast milk.
Vitamin K plays an important role in the treatment and prevention of osteoporosis. Osteoporosis is a disorder characterized by fragile and porous bones, and it affects more than 10 million Americans-80% of which are women. Consumption of calcium and Vitamin D in childhood and adolescence maximizes bone mass and density which can reduce the risk of osteoporosis later in life. Clinical trials have shown that Vitamin K supplementation improves bone strength and density and increases vertebral height in post menopausal women. Vitamin K doses are used as treatment for osteoporosis in Japan, and in Europe it is legal to claim that “a cause and effect relationship has been established between the dietary intake of Vitamin K and the maintenance of normal bone”. The FDA does not yet allow the same sort of claim in the United States.
Vascular calcification reduces elasticity of the arteries and aorta and is a major risk factor for coronary heart disease. Observational studies have shown that dietary intake of Vitamin K is inversely associated with coronary calcification.
Vitamin K has a low potential for toxicity and there are no known levels at which intake has been shown to have deleterious effects.