Vitamin K is a fat-soluble vitamin that plays an important role in blood clotting.

Vitamin K is known as the clotting vitamin, because without it blood would not clot. Some studies indicate that it helps in maintaining strong bones in the elderly.

Vitamin K is found in cabbage, cauliflower, spinach and other green leafy vegetables, cereals, soybeans, and other vegetables. Vitamin K is also made by the bacteria that line the gastrointestinal tract.

Recommendations

Recommended dietary allowances (RDAs) are defined as the levels of intake of essential nutrients that the Food and Nutrition Board judges to be adequate to meet the known nutrient needs of almost all healthy persons.

Specific recommendations for each vitamin depend on age, gender, and other factors (such as pregnancy). The U.S. Department of Agriculture offers a PDF file that lists these recommendations.

Male: 120 mcg

Female: 90 mcg.

It is important for people taking warfarin (a blood thinner) to know that vitamin K or foods containing vitamin K may reduce the effectiveness of this medication. Ask your health care provider before increasing intake or for advice on maintaining proper levels of vitamin K if you are taking warfarin.

Vitamin K deficiency is very rare and occurs when there is an inability to absorb the vitamin from the intestinal tract. Vitamin K deficiency can also occur after prolonged treatment with oral antibiotics.

Individuals with vitamin K deficiency usually have an increased propensity to bruising and bleeding.

Vitamin K is excreted in breast milk, and crosses the placenta. Pregnant women and women who are breast-feeding should consult their health care provider before starting vitamin K supplements.

Phenytoin interferes with the body's ability to use vitamin K. Taking anticonvulsants (such as phenytoin) during pregnancy or while breastfeeding may deplete vitamin K in newborns; consult your obstetrician and/or pediatrician for advice on nutrient replacement therapy.