Vitamin K is a fat-soluble vitamin. Fat-soluble vitamins are stored in the body in the liver and fatty tissues. Unlike the other fat-soluble vitamins, the body actually stores very little vitamin K. This makes regular dietary intake important. Bacteria in the large intestines help by making a range of vitamin K forms called menaquinones. Vitamin K is also produced by plants (phylloquinone) and is primarily found in green vegetables (collards, spinach, salad green, broccoli), brussels sprouts, cabbage, and plant oils. The man-made vitamin K found in supplements is called menadione.
Vitamin K’s functions include:
- Playing an essential role in the blood-clotting process by making the proteins that stop bleeding
- Helping your body make other proteins essential for blood, bones, and kidneys
Adequate Intake (AI)
Vitamin K Deficiency
If you do not get enough vitamin K, your blood will not clot normally. Among healthy people, a deficiency is rare. Symptoms of vitamin K deficiency include:
- Easy bruising and bleeding (nosebleeds, bleeding gums, blood in the urine, blood in the stool, or extremely heavy menstrual bleeding)
- Bleeding in the skull (intracranial hemorrhage) in infants
Vitamin K Toxicity
As a fat-soluble vitamin, vitamin K is stored in the body and not excreted in the urine, like most water-soluble vitamins. While allergic reactions could happen, no symptoms have been observed among people consuming excess amounts of the natural-form of vitamin K. There have been some problems associated with the man-made form of the vitamin (menadione), though. Some infants who were given injections of menadione had liver toxicity, jaundice, and rupture of the blood cells. No tolerable upper intake level (UL)—that is, the highest amount healthy people can consume without endangering their health—has been established for vitamin K. But, to be safe, you should follow the intake guidelines based on your age and gender.
Major Food Sources
Vitamin K Content
|Spinach (fresh/frozen, boiled)||½ cup||360|
|Brussels sprouts(fresh/frozen, boiled)||5 sprouts||289|
|Broccoli (fresh/frozen, boiled)||½ cup||113|
|Cabbage (fresh, boiled)||2/3 cup||98|
|Asparagus (fresh/frozen, boiled)||7 spears||80|
|Soybean oil||1 tbsp||27|
|Canola oil||1 tbsp||21|
|Kiwi fruit||1 medium||20|
|Olive oil||1 tbsp||4|
If You Take a Blood-thinning Drug
If you take a blood-thinning drug (anticoagulant), try to consume the recommended intake of vitamin K (90 mcg). Avoid exceeding this. Taking a vitamin K supplement can cause drug interactions. Talk to your doctor about your how much vitamin K is safe for you.
If You Take Antibiotics
In addition to killing harmful bacteria, antibiotics also destroy the healthful bacteria that live in the intestines and produce vitamin K. You may need to add more foods rich in vitamin K to your diet. Ask your doctor.
If You Have Liver Disease
The liver plays an important role in metabolism and storage of vitamin K. If you have severe liver disease, you may need to take a vitamin K supplement to avoid complications (eg, bleeding or bruising).
If You Have a Newborn Baby
Because vitamin K deficiency can be life-threatening in newborns, the American Academy of Pediatrics recommends that all newborns receive an injection of phylloquinone, a plant-based vitamin K. This is the standard of care in many hospitals.
Tips For Increasing Your Vitamin K Intake
- Slice an avocado. Add a little balsamic vinegar and pepper, and scoop out for a snack. Or, mash the avocado and mix with chopped tomatoes and red onions for a refreshing salsa.
- Pack a kiwi and spoon in your lunch for an afternoon snack. The insides of the kiwi can be scooped out and eaten from this natural and easy container.
- Steam ½ cup broccoli or Brussels sprouts, add lemon juice (1 tbsp), pre-chopped garlic (1 tsp), and Dijon mustard (1 tbsp). Or add broccoli to your favorite lasagna or hot dish.
- Mix 2 (10-ounce) packages of frozen chopped spinach, thawed, well drained, 1 8-ounce package of softened low-fat cream cheese, ¼ cup milk, and 1 teaspoon lemon pepper until well-blended. Spoon into a 1-quart casserole dish and sprinkle with 1/3 cup crushed crackers or seasoned croutons. Bake at 350°F (177ºC) until thoroughly heated (about 25-30 min.).
Abbreviations: mcg = microgram; tbsp = tablespoon; tsp = teaspoon
American Dietetic Association
Canada's Food Guide
Dietitians of Canada
Booth SL, Sadowski JA, Pennington JAT. Phylloquinone (vitamin K1) content of foods in the US Food and Drug Administration’s total diet study. J Agric Food Chem. 1995; 43:1574-1579.
Duyff RL. The American Dietetic Association’s Complete Food and Nutrition Guide. Minneapolis, MN: Chronimed Publishing; 1998.
Garrison R, Somer E. The Nutrition Desk Reference. New Canaan, CT: Keats Publishing; 1995.
Micronutrient information center: vitamin K. The Linus Pauling Institute website. Available at: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminK/. Accessed April 7, 2010.
Vitamin K. EBSCO Natural and Alternative Treatments website. Available at: http://www.ebscohost.com/thisTopic.php?marketID=15topicID=114. Updated February 2010. Accessed April 7, 2010.
Last reviewed April 2010 by Brian Randall, MD
Last updated Updated: 6/15/2011
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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