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Vitamin K: The Last Frontier in Vitamins
Edward Saltzman, M.D.
Dr. Saltzman is Assistant Professor of Medicine, Director, Obesity Consultation Center, and Chief, Division of Clinical Nutrition, Tufts-New England Medical Center, and Scientist II, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University School of Medicine, Boston.
Within the past three years, Dr. Saltzman has been a consultant for Ortho-McNeil and has been on the Speakers' Bureau for Roche and Abbott Pharmaceuticals.
While nutrients such as vitamin E, vitamin C and carotenoids have received substantial attention in the media and the medical literature, vitamin K is seldom mentioned. Traditionally thought to be important only for its role in coagulation, recent advances in vitamin K research suggest that it may have an important role in bone health and vascular disease. The new research also suggests a potentially important interaction between vitamins K and E and, further, that food processing may result in alterations in vitamin K form and function.
Vitamin K: What Is It and Where Does It Come From?
Vitamin K is a fat soluble vitamin found in a variety of food sources. Vitamin K refers to a family of compounds (Figure 1), the most common consumed form being phylloquinone (vitamin K1) which is found in plants.
Figure 1.
Forms of Vitamin K.
Green leafy vegetables are among the richest sources; vegetables account for approximately 60% of vitamin K intake in the US. Vitamin K is also found in some plant oils and products derived from plant oils such as salad dressing or margarine, as well as in an increasing number of dietary supplements, though in low amounts.
When phylloquinone-containing vegetable oils such as soybean, canola or cottonseed are hydrogenated during food processing, a hydrogenated form of vitamin K, dihydro-vitamin K, is also formed. High concentrations of dihydro-vitamin K occur in processed foods, especially fast food French fries, doughnuts and potato chips.
Non-plant forms of vitamin K, the menaquinones (MK), are present in some animal foods and in products derived from bacterial fermentation [e.g., milk, meats, certain organs (liver), fermented soybean products and fermented cheeses].
It has long been believed that approximately half of human vitamin K is derived from the bacteria in our gut, but more recent evidence suggests that most of our vitamin K is derived from outside our bodies and that bacterial sources within the gut are far less important than previously believed.
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