Vitamin K is necessary for healthy blood clotting and for optimal functioning of enzymes needed for bone formation. It is found in green, leafy foods, such as spinach, asparagus and turnip greens, as well as in green tea and beef liver. Besides food sources, bacteria in your intestines make vitamin K. Since your body stores it in your liver and fat tissue, it is rare to be deficient, but it is possible to take too much. No safe upper limit has been established.
Recommended Amounts
Recommendations for daily vitamin K intake for men is 120 mcg; for women, including pregnant and breastfeeding women, it is 90 mcg. The recommended amount is 75 mcg for 14- to 18-year olds. The recommended amount for children ages 9 to 13 is 60 mcg and for ages 4 to 8, 55 mcg. For ages 1 to 3, it drops to 30. Recommendations for infants are much lower -- only 2 mcg for the first six months of life and 2.5 mcg from six months to a year. It is safest to get vitamin K from diet, rather than through supplementation.
Interactions With Medications
Too much vitamin K decreases the blood-thinning effect of aspirin and Coumadin -- generic name, warfarin. Your doctor needs to know the kinds and amounts of foods you regularly eat that contain vitamin K in order to calculate your Coumadin dosage. Do not change your diet or take vitamin K supplements without first talking with your doctor. Like vitamin K, coenzyme Q-10 promotes blood clotting. Taking both increases blood clotting, which can negate any blood-thinning effects of Coumadin or aspirin.
Liver and Kidney Diseases
Clotting factors are produced by the liver. The inability to make clotting factors can be one result of severe liver disease. Unfortunately, vitamin K cannot help in this instance and too much vitamin K may even make the problem worse. If you are on dialysis for severe kidney disease, avoid vitamin K supplementation. The vitamin is not removed by dialysis. Blood thinners are used to prevent clotting and too much vitamin K interferes with their action.
Pregnancy and Breastfeeding
The amounts of vitamin K in a healthy diet is generally considered safe for pregnant and breastfeeding women, but talk to your doctor before taking vitamin K supplements. The vitamin is able to cross the placenta, which means your fetus will get some of any vitamin K you take. Vitamin K is also excreted in breast milk.
G6PD Deficiency and Hemolysis
Some people are unable to produce enough of an enzyme called glucose-6-phosphate dehydrogenase, or G6PD, which protects red blood cells from by-products of medications and infection. When there is not enough, red blood cells can be destroyed, resulting in anemia. If you or your child has this condition, discuss vitamin K intake with your doctor. Excessive amounts can destroy red blood cells under normal conditions and any amount may be dangerous to people with a G6PD deficiency.
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