Merck Manual

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Vitamin K Excess

(Vitamin K Toxicity)


Larry E. Johnson

, MD, PhD, University of Arkansas for Medical Sciences

Last full review/revision Nov 2020| Content last modified Nov 2020
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Vitamin K toxicity is rare but is most common in formula-fed infants. 

Vitamin K has two forms:

  • Phylloquinone: This form occurs in plants and is consumed in the diet. It is absorbed better when it is consumed with fat. Phylloquinone is not toxic, even in large amounts.

  • Menaquinone: This form is produced by bacteria in the intestine, but only small amounts of it are produced. In some countries, this form is used for supplementation.

Vitamin K is necessary for normal blood clotting. It is also needed for healthy bones and other tissues.

The effects of vitamin K toxicity can include anemia due to rupture of red blood cells and jaundice. Jaundice in newborns can cause kernicterus (a type of brain damage). 

(See also Overview of Vitamins.)

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