In this Article

• What are vitamins, and why are they important?
• Calcium
• Vitamin D
• Folic acid
• Vitamin E
• Vitamin A
• Vitamin C
• Vitamin B12
• Vitamin B6
• Thiamin (vitamin B1)
• Niacin
• Riboflavin
• Vitamin K
• Vitamins and Calcium Supplements Glossary
• Vitamins and Calcium Supplements Index

Vitamin K

What is vitamin K, and what does it do?

Vitamin K is a fat-soluble vitamin known for its role in blood clotting. There are three main types of vitamin K: vitamin K1 (phytonadione) if the natural form found in plants; vitamin K2 (menaquinones) is made by the human gut; and vitamin K3 (menadione) is the water-soluble form that is made for use in supplements.

People taking the blood-thinning medication warfarin (Coumadin) are at an increased risk for blood clotting. Warfarin works by decreasing the activity of vitamin K, lengthening the time it takes for a clot to form. The goal for vitamin K intake while taking warfarin is to keep your intake constant. This does not mean that you can't consume any vitamin K-containing foods. Instead, you want to consume a consistent amount so that the dose of warfarin that you are taking is working on the same amount. Sudden increases and/or decreases in vitamin K while taking warfarin can cause problems.

How much vitamin K do I need to consume?

There is no data to establish RDAs for vitamin K. Therefore, Adequate Intakes (AI) have been established:

What are sources of vitamin K?

Vitamin K is found primarily in green leafy vegetables and fruit. It can also be found in some animal foods.

For more sources go to http://www.nal.usda.gov/fnic/foodcomp/Data/SR20/nutrlist/sr20a430.pdf.

Do I need to take a vitamin K supplement?

A well-balanced diet can provide an adequate amount of vitamin K. There are conditions that can interfere with the absorption of vitamin K, including celiac disease, ulcerative colitis, cystic fibrosis, biliary obstruction, regional enteritis, or intestinal resection. Medications that alter your liver function or kill the intestinal flora can also negatively impact your vitamin K levels. These medications include antibiotics, antiseizure medications, salicylates, and some sulfa drugs.

What happens if I don't have enough vitamin K?

Vitamin K is needed by the liver to make factors that are necessary for blood to clot properly. A deficiency in vitamin K can lead to defective blood clotting and increased bleeding.

Is there such a thing as too much vitamin K?

The Tolerable Upper Limit (UL) for vitamin K has not been established. Amounts exceeding 1,000 times the AI can promote formation of blood clots (thrombogenesis), breakdown of red blood cells (hemolysis), and raise the risk of jaundice.