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Vitamin K is a fat-soluble vitamin, meaning that it dissolves in fat rather than in water. Vitamin K is carried through the body by fat and is stored in fat tissue. Thus, instead of being excreted from the body, it can accumulate to excess and cause toxicity if too much is taken in.

There are three forms of Vitamin K:

• phylloquinone, which is found in food
• menadione, which is man-made
• menaquinone, which is produced by the body

What food source is the nutrient found in?

• collards, kale, and other green leafy vegetables
• members of the cabbage family including broccoli, cauliflower, and Brussels sprouts
• liver
• cheese
• milk
• egg yolk
• some fruits

Intestinal bacteria produce some vitamin K in the body.

How does the nutrient affect the body?

Vitamin K makes several proteins that help blood to clot when bleeding. It also makes other proteins for blood, bones, and kidneys. Along with vitamins A and D, vitamin K is important for strong bone development.

Information

The Recommended Dietary Allowance, called RDA, for vitamin K for adult males, age 25 years and older, is 80 micrograms (mcg) per day. For women, age 25 years and older, it is 65 mcg per day. For pregnant and lactating women, the RDA is also 65 mcg.

Vitamin K deficiency is rare. When it occurs, it is often the result of impaired absorption rather than not getting enough in the diet. Newborns are at risk for vitamin K deficiency, because their digestive tracts contain no vitamin K-producing bacteria. For this reason, doctors often give injections of vitamin K to newborns. Prolonged use of antibiotics can also cause a low level of this vitamin because they destroy some of the bacteria in the gut that help to produce vitamin K.

The main symptom of vitamin K deficiency is slowed blood clotting. Those who are taking blood thinning medicines, such as aspirin or warfarin, may need to limit their intake of vitamin K-rich foods. This is because the vitamin's pro-clotting actions can work against this type of medicine.

Toxicity from too much vitamin K is uncommon, but flushing, sweating, jaundice, and anemia have been reported following excessive consumption of vitamin K supplements. Moderation in this, as with all supplements, is the best approach.