Vitamin K-Controlled Diet

Vitamin K is a fat-soluble vitamin whose primary function in your body is to promote blood clotting. Vitamin K is actually a family of three closely related nutrients, two of which are found in nature. Phylloquinone, or vitamin K-1, is found in foods. Menaquinone, or vitamin K-2, is produced by bacteria in your intestine. Menadione, or vitamin K-3, is a synthetic compound used by physicians to enhance clotting in people who may not use vitamin K well. In certain situations, dietary restriction of vitamin K is necessary to reduce clotting.

Function

Whenever you sustain an injury, your blood coagulates to prevent excessive hemorrhage. The coagulation process is complex, requiring the participation of cellular components called platelets and an array of proteins called clotting factors, which are produced in your liver. Several clotting factors cannot become fully functional until they undergo an enzymatic conversion prior to their release into your bloodstream. Vitamin K is an essential cofactor for this enzyme, but it is itself "deactivated" with each conversion of a clotting factor. According to a 2008 review in "Vitamins and Hormones," vitamin K is efficiently renewed in an enzymatic loop called the vitamin K cycle.

Warfarin

Some medical conditions -- artificial heart valves, abnormal heart rhythms or recurrent clots in your legs or lungs -- require a "thinning" of your blood to prevent inappropriate clotting. The most commonly prescribed medication for this purpose is warfarin, which interferes with the vitamin K cycle and consequently reduces the synthesis of clotting factors. When your doctor prescribes warfarin, he or she may ask you to limit your intake of vitamin K, because higher blood levels of vitamin K can overcome warfarin's therapeutic effects.

Vitamin K Foods

Some of the most abundant dietary sources of vitamin K are leafy greens, such as kale, collards, spinach, turnip and beet greens, parsley and mustard greens. Other vegetables such as broccoli, brussels sprouts, endives and asparagus are also rich in vitamin K. Okra, cabbage, plums, prunes, rhubarb and black-eyed peas are fairly high in vitamin K. The U.S. Department of Agriculture offers valuable information on the vitamin K content of various foods.

Considerations

Although vitamin K restriction has traditionally been recommended for people taking warfarin, your physician may be comfortable with you consuming vitamin K-containing foods. Because the foods that contain vitamin K also contain other valuable nutrients, many doctors simply adjust your warfarin dosage to match your usual intake of these items. As long as your diet remains relatively constant, your blood's clotting ability will remain stable. However, problems can arise if you suddenly increase your intake of greens or other vegetables. Ask your doctor whether you should restrict your intake of vitamin K.