Health Benefits of Vitamin K
The best understood function of vitamin K is its essential role in the process of blood coagulation. When someone is vitamin K deficient, their blood does not clot normally when they are cut and it is difficult to stop the bleeding.But, there is copious evidence that vitamin K also plays an extremely important role in maintaining the health of bones. Many studies have reported that low vitamin K intake increases the risk of developing osteoporosis. Vitamin K is essential for the normal formation of a protein in bones called osteocalcin. This protein binds to calcium and helps to hold the calcium in the bones.
Vitamin K also appears to help prevent cardiovascular disease. Part of the plaque that accumulates in arteries when they become narrowed in the development of arteriosclerosis is composed of calcium. Vitamin K plays a role that prevents this accumulation of calcium and reduces the risk of cardiovascular disease.
How Much Vitamin K Do You Need?
The current U.S. “Adequate Intake” (AI) value for vitamin K obtained from foods is 90 micrograms per day for women and 120 for men. However, these recommendations are somewhat controversial. Although this amount of vitamin K is adequate to promote normal blood clotting, many vitamin K researchers are finding that greater intake is likely needed for optimal bone health. European researchers from five countries recently suggested that 200 to 500 micrograms per day of vitamin K from foods (or about 100 micrograms from supplements) is likely needed for optimal bone health. Many studies have evaluated doses of vitamin K that are ten times these recommended intakes or greater.Cooked dark green vegetables typically provide between 50 and 500 micrograms of vitamin K per half-cup serving. In general, the vitamin K in vegetables is not absorbed very efficiently. The AI values given above are recommendations for the amount of vitamin K from foods. The form of vitamin K in supplements is absorbed by the body 5 to 10 times more efficiently than it is from green vegetables. Consequently, 100 micrograms of vitamin K in a supplement may be comparable to 500 micrograms from food sources.
Can you get too much vitamin K?
Fortunately, vitamin K has low toxicity. No upper limit has been established in the United States. However, guidelines for upper levels of intake specifically from nutritional dietary supplements were developed by the Food Standards Agency of the United Kingdom and published online as part of their publication Safe Upper Levels for Vitamins and Minerals (available in a large pdf file). The agency set a provisional “guidance level” for adults of one milligram per day (1000 micrograms) for the maximal level of safe lifelong intake of vitamin K from supplements for adults. Studies on bone function indicate that there is no reason to exceed 1000 micrograms per day.
Caution for Those Taking “Blood Thinner” Drugs
Vitamin K counteracts the function of anticoagulant or “blood thinner” types of drugs. Consequently, people taking these anticoagulant drugs must work closely with their physician if they want to change the level of their vitamin K intake.There is some evidence that those taking anticoagulants may not need to forgo the benefits of vitamin K. Researchers in The Netherlands recently reported that, “. . . supplements providing 100 micrograms per day of vitamin K do not significantly interfere with oral anticoagulant therapy.” But don’t try this without medical supervision.
Vitamin K in Supplements
There are two main forms of vitamin K found in dietary supplements. It is likely that they are both equally effective, although future research is needed to clarify this. Vitamin K-1 (phylloquinone) is the form of vitamin K most commonly available in supplement form. Another form, vitamin K-2 (menaquinones) appears to be equally effective. Vitamin K-1 is the form present in plants and K-2 is produced by bacteria in the lower intestine.
Interactions with Other Vitamins
There is some evidence that high doses of vitamin A and vitamin E can interfere with the benefits of vitamin K. The amounts of vitamin A and E in common multivitamin supplements are unlikely to generate this potential problem.
Synergy with Other Nutrients
None of the bone-benefitting nutrients seem to have a major effect by themselves. In other words, there is no one “magic bullet.” Increased vitamin K intake is likely to be best for bones when you also are getting enough of the other bone nutrients like vitamin D and calcium.See page 2 for vitamin K resources that may be of interest to your physician.