Vitamin K is a fat-soluble vitamin that's needed for normal blood clotting and bone metabolism. It binds to calcium, which activates blood clotting factors. Vitamin K is found in foods mostly of plant origin, but there are smaller amounts in meats and seafood. Your intestinal bacteria synthesize a form of vitamin K called menaquinone in the colon. It's also available as a dietary supplement.
Seafood
Fish and seafood are generally lower in vitamin K than most plant sources. A 3 oz. serving of light tuna packed in oil has the most, according to the U.S. Department of Agriculture, with 37.4 mcg. A 3 oz. serving of sardines contains 2.2 mcg, 3 oz. white tuna packed in water has 2.1 mcg, 3 oz. orange roughy has 0.9 mcg, 1/2 salmon filet has 0.8 mcg, 6 oysters and a 3 oz. serving of lobster both contain 0.1 mcg.
Sources of Vitamin K
Dark green leafy vegetables and cruciferous vegetables are excellent sources of vitamin K. One cup of cooked kale has 1,146.6 mcg and 1 cup of cooked spinach has from 888.5 to 1,1027.3 mcg. One cup of brussels sprouts has 299.9 mcg, 1 cup green onions has 207.0 mcg, 1 cup raw spinach has 144.9 mcg and 1 cup of raw broccoli has 89.4 mcg.
Dietary Reference Intakes
The Food and Nutrition Board of the Institutes of Medicine determined the dietary reference intakes for vitamin K are 2.0 mcg for infants ages 0 to 6 months and 2.5 mcg for infants ages 7 to 12 months. Children ages 1 to 3 years need 30 mcg, while children ages 4 to 8 need 55 mcg, and children ages 9 to 13 need 60 mcg. Teenagers need 75 mcg per day. Men need 120 mcg per day and women need 90 mcg per day.
Vitamin K Interactions
According to the Linus Pauling Institute, large doses of vitamin A interfere with absorption of vitamin K, and vitamin E inhibits some enzymes that depend on vitamin K. Prolonged use of antibiotics may reduce the intestinal bacteria's ability to make vitamin K. Large doses of vitamin K from dietary supplements may interfere with anticoagulant medications. Your doctor can help you determine how much vitamin K you need if you're on anticoagulant medications. Speak to your doctor before taking vitamin K supplements.
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