Vitamin K is needed for proper bone formation and blood clotting. In both cases, vitamin K does this by helping the body transport calcium. Vitamin K is used by doctors when treating an overdose of the drug warfarin. Also, doctors prescribe vitamin K to prevent excessive bleeding in people taking warfarin but requiring surgery.
Where is it found?
Leafy green vegetables, such as spinach, kale, collards, and broccoli, are the best sources of vitamin K. The greener the plant, the higher the vitamin K content.1 Other significant dietary sources of vitamin K include soybean oil, olive oil, cottonseed oil, and canola oil.2
Vitamin K has been used in connection with the following conditions (refer to the individual health concern for complete information):
| Science Ratings | Health Concerns |
|---|---|
 |
Celiac disease (for deficiency only) |
 |
Acute myeloid leukemia (vitamin K2 only) Myelodysplastic syndromes (vitamin K2 only) Phenylketonuria (if deficient) |
 Reliable
and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies
suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but minimal
or no scientific evidence. For a supplement, little scientific support and/or minimal health
benefit. |
|
Who is likely to be deficient?
A vitamin K deficiency, which causes uncontrolled bleeding, is rare, except in people with certain malabsorption diseases. However, there are reports of severe vitamin K deficiency developing in hospitalized patients who had poor food intake and were receiving antibiotics.3 All newborn infants receive vitamin K to prevent deficiencies that sometimes develop in breast-fed infants.
How much is usually taken?
The recommended dietary allowance for vitamin K is about 1 mcg per 2.2 pounds of body weight per day or about 65 to 80 mcg per day for most adults.4 This level of intake may be achieved by consuming adequate amounts of leafy green vegetables. However, studies have shown that many men and women aged 18 to 44 years ingest less than the recommended amount of vitamin K.5 6
Are there any side effects or interactions?
Allergic reactions to vitamin K injections have been reported on rare occasions.7
Vitamin K facilitates the effects of calcium in building bone and proper blood clotting.
Are there any drug
interactions?
Certain medicines may interact with vitamin K. Refer to drug interactions for a list of those medicines.
1. Kodaka K, Ujiie T, Ueno T, Saito M. Contents of vitamin K1 and chlorophyll in green vegetables. J Jpn Soc Nutr Food Sci 1986;39:124–6.
2. Booth SL, Centurelli MA. Vitamin K: a practical guide to the dietary management of patients on warfarin. Nutr Rev 1999;57:288–96 [review].
3. Pineo GF, Gallus AS, Hirsh J. Unexpected vitamin K deficiency in hospitalized patients. Can Med Assoc J 1973;109:880–3.
4. Food and Nutrition Board, National Research Council. Recommended Dietary Allowances, 10th ed. Washington, DC: National Academy Press, 1989.
5. Booth SL, Suttie JW. Dietary intake and adequacy of vitamin K. J Nutr 2000;130(1S Suppl):785–8.
6. Booth SL, Webb DR, Peters JC. Assessment of phylloquinone and dihydrophylloquinone dietary intakes among a nationally representative sample of US consumers using 14-day food diaries. J Am Diet Assoc 1999;99:1072–6.
7. Wong DA, Freeman S. Cutaneous allergic reaction to intramuscular vitamin K1. Australas J Dermatol 1999;40:147–52.
