Vitamin K is an important nutrient that aids in blood clotting and helps your body develop strong, healthy bones. Your age and gender dictate how much vitamin K your body needs daily, with recommended daily intakes ranging from 2 micrograms in infants to 90 in pregnant or breast-feeding women. Despite the importance of this vitamin, certain people shouldn't take vitamin K supplements and should limit their dietary intake of vitamin K-rich foods, such as green leafy vegetables.
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Glucose-6-Phosphate Dehydrogenase Deficiency
Glucose-6-phosphate dehydrogenase deficiency, or G6PD, is a genetic disorder that affects an estimated 400 people in the world and causes jaundice, pale skin, fatigue, increased heart rate, shortness of breath and fatigue. The use of vitamin K by people with G6PD is controversial. Health professionals with the University of Maryland Medical Center warn against it, while the Council for Responsible Nutrition reports that concerns about adverse effects of vitamin K supplements in people with G6PD are unfounded and exaggerated. If you have G6PD, consult your doctor before using vitamin K supplements.
Kidney or Liver Disease
People with preexisting kidney or liver disease should avoid taking vitamin K supplements. Organ damage caused by these diseases might make it harder for your liver or kidneys to filter vitamin K waste products from your body. Consequently, you might be at risk of developing unusually high blood vitamin K levels, a condition called hypervitaminosis K.
Use of Certain Medications
Vitamin K might negatively interact with certain medications. If you are taking blood thinners, such as warfarin, you should maintain a low vitamin-K diet and avoid treatment with vitamin K supplements. Consuming vitamin K in conjunction with blood thinners reduces the effects of these medications.
Although vitamin K is necessary during pregnancy and lactation, expectant or lactating mothers should talk with a doctor before taking a nutritional supplement, including vitamin K. Certain medications also might interfere with your body's ability to absorb vitamin K. Such drugs include antibiotics, orlistat, bile acid sequestrants and phenytoin. In addition, large doses of vitamins A and E also might limit your ability to absorb vitamin K.