Blood Clotting and Vitamin K

Prothrombin and Platelet Interaction

• The Gla residues of prothrombin have a strong chelating effect on positively charged calcium ions due to their two adjacent, negatively charged carboxylate groups.
• The prothrombin-calcium complex binds to phospholipids on the surface of platelets, essential for blood clotting.
• Attachment to platelets increases the rate of proteolytic conversion of prothrombin to thrombin.

Vitamin K Distribution and Requirement

• Vitamin K is found in various food sources, including cabbage, kale, spinach, egg yolk, and liver.
• The bacteria in the gut also synthesize vitamin K.
• The recommended daily intake of vitamin K is 120 µg for adult males and 90 µg for adult females.

Vitamin K Deficiency in Newborns

• Newborns have sterile intestines, lacking the bacteria that synthesize vitamin K.
• Human milk provides only about one-fifth of the daily requirement for vitamin K.
• A single intramuscular dose of vitamin K is recommended for newborns as prophylaxis against hemorrhagic disease.

Vitamin K Toxicity

• Prolonged administration of large doses of synthetic vitamin K (menadione) can cause hemolytic anemia and jaundice in infants.
• Toxic effects occur due to damage to red blood cell membranes.
• Synthetic vitamin K is no longer used to treat vitamin K deficiency.
• There is no established upper limit for vitamin K consumption.