Also called the anti-hemorrrhagic factor, vitamin K was first discovered by a Danish scientist who demonstrated its role in blood coagulation. The Danish spelling is “koagulation”, hence the letter K designation. Substances with vitamin K activity are quinones. K1 or phylloquinone is present in green leaves; K2 or famoquinone was isolated from putrefied fishmeal. K3 or menadione is a synthetic form. There are some synthetic water-soluble vitamins (e.g. Synkayvite and Hykinone) for vitamin K administration and for clinical use when fat absorption is impaired. The reference standard is menadione. One unit vitamin K = 1 microgram menadione.
Vitamin K is readily available in both plant and animal based food.
a. Animal Sources
Includes organ meat such as liver and egg yolk contain or are rich sources of vitamin K.
b. Plant Sources
Dark green leaves, wheat bran, vegetable oils, especially soybean oil and wheat germ oil are excellent food sources. Good amounts are present in tomatoes, tubers, seeds and legumes.
Benefits and Therapeutic Effects
The most important biological role of vitamin K is the maintenance of prothrombin level in blood plasma. The coagulation of blood is a series of reactions that depend on several factors. Prothrombin and Proconvertin are among these and vitamin K is needed in the synthesis of both. Students, especially nutrition majors, are encouraged to probe further on blood coagulation by referring to a recent biochemistry or physiology textbook.
Vitamin K is also needed in phosphorylation, a chemical process that adds the phosphate radical to glucose so that its passage through cell membranes is hastened.
In lower animals, Vitamin K is essential for cellular respiration, and in plants, photosynthesis requires vitamin K.
The less known function of vitamin K which was recently observed is to help synthesize osteocalcin, a protein found in the bones. The function of osteocalcin, which is the second most abundant type of protein in the bones, is to bind calcium.
Signs of Deficiency
Deficiency in vitamin K results in hemorrhagic disease in the newborn and delayed blood clotting time in adults. Dietary deficiency of vitamin K rarely occurs; inadequacy may be conditioned or induced by intestinal and liver disorders, obstruction of the bile duct and the use of antivitamins.
Exact amounts of vitamin K requirement are not known due to intestinal synthesis and variable content in food sources. It is assumed that an average mixed diet has normal vitamin K intakes for most individuals. However, a normal dose of 1 to 2 milligrams is adequate for prophylaxis.
Side Effects and/or Toxicity
Excessive vitamin K is not observed to an extent as hypervitaminosis A or D, unless massive doses of the synthetic form have been administered. The toxic effects of vitamin K are: vomiting, hemolysis and albuminuria. Kenicterus is a condition resulting from the accumulation of bile pigments in the gray matter of the central nervous system. This has been observed in infants with uncontrolled synthetic vitamin K therapy.
Vitamin K is an essential nutrient in our body and although its toxicity in excess amounts have not been demonstrated in man compliance of its dosages is recommended for safety purposes.