Vitamin K helps bones, brain and eyes
YOU probably know that vitamin K is needed for normal blood clotting, but did you know that vitamin K could benefit the health of bones, blood vessels, brain cells, and eyes?
Vitamin K is thought to contribute to bone health by helping bones retain calcium. In combination with nutrients like calcium and vitamin D, vitamin K appears to help maintain bone mass and prevent bone loss with aging.
In contrast to helping bones retain calcium, vitamin K benefits cardiovascular health by preventing calcium accumulation in blood vessels. This helps to avoid the "hardening of the arteries" commonly associated with cardiovascular disease.
Recent research also indicates that vitamin K could contribute to both brain and eye health. The vitamin appears to help reduce the risk of developing age-related dementia and macular degeneration.
Question: Since common "blood thinner" drugs help to prevent strokes function by blocking vitamin K function, do these drugs prevent the benefits of vitamin K?
Answer: Drugs like Coumadin (warfarin) do not appear to adversely affect bones, according to recent studies. However, some research indicates that calcification of arteries (hardening of the arteries) might be an adverse side effect of some blood thinners. Certainly, stroke prevention is the most immediate concern. However, current medical thinking typically emphasizes adjusting drug dosage to a consistent daily vitamin K intake that is adequate. This avoids major fluctuations from day to day.
Q: How much vitamin K intake is recommended?
A: The Institute of Medicine recommends that normal healthy adults consume 90 to 120 micrograms of vitamin K per day from the foods in their diet. Interestingly, the forms of vitamin K in supplements are absorbed five to 10 times more efficiently than the natural vitamin K in foods. So, 10 micrograms in a supplement is similar to 50 to 100 in foods.
Due to low toxicity, no upper limit has been established for vitamin K intake in the United States. The Food Standards Agency of the United Kingdom, however, suggests 1,000 micrograms per day as the maximal level of safe intake of vitamin K from supplements for a normal healthy individual not taking blood thinner drugs.
Q: What foods provide vitamin K?
A: Cooked dark green vegetables are rich sources, containing between 50 and 500 micrograms of vitamin K per half-cup serving.
Modest amounts also are found in soybean and canola oils. Some fermented foods, like natto, contain variable amounts of a form called vitamin K-2.
Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S. are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dr. Dobbs also works with University Health Services.