Vitamin K

  • Definition
    • Vitamin K is a fat-soluble vitamin.

  • Alternative Names
    • Phylloquinone; K1; Menaquinone; K2; Menadione; K3

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

  • Food Sources
    • The best way to get the daily requirement of vitamin K is by eating food sources. Vitamin K is found in the following foods:

      • Green leafy vegetables, such as kale, spinach, turnip greens, collards, Swiss chard, mustard greens, parsley, romaine, and green leaf lettuce
      • Vegetables such as Brussels sprouts, broccoli, cauliflower, and cabbage
      • Fish, liver, meat, eggs, and cereals (contain smaller amounts)

      Vitamin K is also made by the bacteria in the lower intestinal tract.

  • Side Effects
    • Vitamin K deficiency is very rare. It occurs when the body can't properly absorb the vitamin from the intestinal tract. Vitamin K deficiency can also occur after long-term treatment with antibiotics.

      People with vitamin K deficiency are often more likely to have bruising and bleeding.

      If you take blood thinning drugs (such as anticoagulant/antiplatelet drugs), you may need to limit vitamin K foods. You may also need to eat a consistent amount of vitamin K containing foods on a day to day basis if you consume these foods. You should know that vitamin K or foods containing vitamin K can affect how these drugs work.

      It is important for you to keep vitamin K levels in your blood about the same from day to day. Ask your health care provider how much vitamin K-containing foods you should eat.

  • Recommendations
    • The Recommended Dietary Allowance (RDA) for vitamins reflects how much of each vitamin most people should get each day.

      • The RDA for vitamins may be used as goals for each person.
      • How much of each vitamin you need depends on your age and gender.
      • Other factors, such as pregnancy, breast-feeding, and illness may increase the amount you need.

      The Food and Nutrition Board at the Institute of Medicine Recommended Intakes for Individuals - Adequate Intakes (AIs) for vitamin K:


      • 0 to 6 months: 2.0 micrograms per day (mcg/day)
      • 7 to 12 months: 2.5 mcg/day


      • 1 to 3 years: 30 mcg/day
      • 4 to 8 years: 55 mcg/day
      • 9 to 13 years: 60 mcg/day

      Adolescents and Adults

      • Males and females age 14 to 18: 75 mcg/day
      • Males and females age 19 and older: 90 mcg/day for females (including those who are pregnant and lactating) and 120 mcg/day for males
  • References
    • Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron Manganese, Molybdenium, Nickel, Silicon, Vanadium, and Zinc. National Academy Press. Washington, DC, 2001. PMID: 25057538

      Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 225.

      Salwen MJ. Vitamins and trace elements. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 26.