Vitamin K

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 helps make six of the 13 proteins needed for blood clotting. Its role in maintaining the clotting cascade is so important that people who take anticoagulants such as warfarin (Coumadin) must be careful to keep their vitamin K intake stable.

Vitamin K is also involved in building bone. Low levels of circulating vitamin K have been linked with low bone density, and supplementation with vitamin K shows improvements in biochemical measures of bone health. A report from the Nurses' Health Study suggests that women who get at least 110 micrograms of vitamin K a day are 30% less likely to break a hip as women who get less than that. Among the nurses, eating a serving of lettuce or other green leafy vegetable a day cut the risk of hip fracture in half when compared with eating one serving a week. Data from the Framingham Heart Study also shows an association between high vitamin K intake and reduced risk of hip fracture.

The recommended daily intake for vitamin K is 80 micrograms for men and 65 for women.

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.

Food Sources: 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.

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.