Reprinted from the LA Times, November 15, 1999
Vitamin K Is Essential to Blood-Clotting Process
By SHELDON MARGEN, DALE A. OGAR
Several readers wrote to us recently with questions about vitamin K.
It seems that most people pay little or no attention to this unusual vitamin until they start taking anticoagulant drugs to prevent blood clots. Then, if their doctors are on top of things, they will be advised to cut down on their vitamin K intake. At this point, most folks say, "Vitamin what?"
Vitamin K is one of the fat soluble vitamins (like vitamins A, D and E), but unlike those more familiar substances, not much of it is stored in the body. Fortunately, however, about 80% of the vitamin K we need is synthesized by the bacteria that normally live in our intestinal tracts.
Without vitamin K, your blood would not clot. The process by which this works is very complex, but, basically, vitamin K acts as a catalyst that transforms some anticlotting proteins, which are always present, into clotting proteins when there is a cut or wound to the body.
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For those of you interested in how things get discovered, we have the Danes to thank for figuring this one out. Back in the 1930s, scientists in Copenhagen found out that chicks, which were fed a fat-free diet, suffered from bleeding problems. Eventually the researchers figured out that there was a substance in alfalfa that cured the condition. They named it vitamin K, for the Danish word Koagulation.
The recommended daily allowances for vitamin K are relatively modest, between 60 mcg and 80 mcg, depending on age and gender.
Deficiencies are extremely rare in healthy people. However, they can occur in people who have certain malabsorption syndromes, liver disease or who are taking long-term antibiotic therapy. Also, some infants do not have the necessary intestinal bacteria to manufacture vitamin K and may need supplementation for a period of time.
The biggest worry these days about vitamin K is for people who have circulatory or cardiovascular disease and are put on blood-thinning drugs such as Coumadin or Warfarin. These drugs can interfere with the body's own production of vitamin K, and in case of a serious injury, it may be difficult to stop the bleeding. However, physicians who prescribe such drugs generally monitor the vitamin K status of their patients.
In an everyday diet, healthy people would have a difficult time getting too much vitamin K because it is only abundant in leafy green vegetables, broccoli and Brussels sprouts. Other vegetables, fruits and some fats have smaller amounts.
One interesting misconception about vitamin K is that green tea is the richest food source and that drinking green tea (which we have recommended for its other valuable components) would be dangerous for people who need to control their vitamin K intake. This is only true, however, if you eat the leaves instead of brewing them into tea.
One other important fact to keep in mind is that very high doses of vitamin E (probably above the levels we recommend) can interfere with vitamin K functioning because vitamin E not only serves as an antioxidant, but also as a mild anticoagulant.
This reinforces our continuing advice that anybody who is taking any kind of supplements should inform their primary health-care provider so that possible interactions and contraindications can be taken into account.
Always tell your doctor everything you are taking.
So, what should you do if your doctor tells you to watch your vitamin K intake? After years of advising people to eat more green vegetables because of all the health-promoting substances they contain, it may be hard to figure out how to eliminate those very same foods from the diet and still get the benefit of their vitamins, minerals, fiber and antioxidants.
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Fortunately, most of the good stuff in broccoli is also available in other foods that may have a lower vitamin K content. Citrus fruits can fill in the vitamin C content. Many of the carotenoids can be found in other dark green or otherwise brightly colored vegetables and fruits. Some of the so-called cancer-fighting compounds in broccoli may be harder to replace, but for individuals with known cardiovascular and atherosclerotic disease, this is a reasonable trade-off.
About a year ago we received a copy of an interesting cookbook that was written to help individuals who are taking anticoagulant drugs plan their diets in a healthy and appropriate way. It is written by Dr. Rene Desmarais, Gregory Golden and Gail Beynon and is called "The Coumadin Cookbook: A Complete Guide to Healthy Meals When Taking Coumadin." It is available from the publisher (Marsh Publishing, P.O. Box 1597, Salisbury, MD 21802-1597;  749-1989). It provides lists of foods that are low in vitamin K, is full of great recipes and gives many good suggestions for how to calculate the amount of vitamin K you ingest.
If you would like to receive a list of foods high in vitamin K, you can send a self-addressed, stamped envelope to Dale Ogar, School of Public Health, UC Berkeley, Berkeley, CA 94720-7360. Mark the outside of envelope "Vitamin K."
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