Vitamin K is also sometimes given by injection to women prior to labor (a deficiency can occur during pregnancy) or to patients before or after surgery to prevent hemorrhage. Higher doses of vitamin K than are needed by the body do not cause excessive blood clotting, so this is not a concern. Additional K is given at times to women with heavy menstrual flow, to help relieve menstrual pain, or to reduce the nausea and vomiting of pregnancy. It is also used to promote blood clotting in people with liver disease, jaundice, or malabsorption problems. Those people who bruise easily or whose blood clots slowly after injury sometimes benefit from supplemental vitamin K, as do some sufferers of rheumatoid arthritis, where K may reduce irritation in the synovial linings of the joints.

An occasional use of vitamin K that can be lifesaving is the treatment of people who have taken too much of the anticoagulant Coumadin. People with strokes, heart attacks, thrombophlebitis, or pulmonary embolism or who are at risk of having problems related to abnormal blood clotting may receive this type of anticoagulant therapy. As I described previously, the coumarol medications reduce blood clotting by competing with vitamin K sites and reducing prothrombin formation. If bleeding problems occur in patients on Coumadin therapy, an injection of vitamin K may help correct it rapidly. Vitamin K is also used at times as a preservative in foods; it helps control fermentation. If vitamin K deficiency is suspected, it is usually wise to consume more foods high in this vitamin before using supplements.

Deficiency and toxicity: Toxicity rarely occurs from vitamin K from its natural sources—that is, from foods or from production by the intestinal bacteria—but toxic side effects are more likely from the synthetic vitamin K used in medical treatment. Natural vitamins K1 and K2 are easily stored or eliminated, whereas menadione, or K3, can build up in the blood and cause some toxicity. Hemolytic anemia, a reduction in red blood cells due to destruction, is a possible problem. This usually increases the bilirubin, one of the breakdown products of hemoglobin in the blood, more of a problem in infants, who have a harder time handling high levels of bilirubin. Symptoms of adult toxicity may include flushing, sweating, or a feeling of chest constriction; however, problems arising from vitamin K use are rare.

Deficiency of vitamin K is also uncommon. It is more likely with poor intestinal absorption, with low dietary intake or decreased production in the intestines, or when the liver is not able to use vitamin K (which may be caused by either a genetic condition or liver disease). Deficiency of vitamin K is also more common in sprue or celiac disease (intestinal malabsorption problems), in colitis, in ileitis, or after bowel surgery. I mentioned that for a few days the newborn baby is at risk of bleeding because of lack of vitamin K; vitamin K deficiency may also be a problem in the elderly, when the diet is poor or when antibiotic use or other factors decrease intestinal bacterial production.

The problems that may occur from vitamin K deficiency involve abnormal bleeding, as in nosebleeds and internal hemorrhage, which can be severe if it occurs in the brain or internal organs. Miscarriage may occur secondary to bleeding problems from vitamin K deficiency in pregnancy. Fortunately, this is uncommon.

Requirements: There is no official RDA for vitamin K (there may be one soon), as there is usually sufficient supply from foods and intestinal bacteria. An average diet will usually provide at least 75–150 mcg., which is the suggested minimum, though 300 mcg. daily may be optimal. Absorption may vary from person to person, estimated from 20–60 percent of intake. Overall, suggested needs are about 2 mcg. per kilogram (2.2 pounds) of body weight.