Clinical Biochemistry: Vitamins K and E

Vitamin K

• Vitamin K is an anti-hemorrhagic factor, and its deficiency produces uncontrolled hemorrhages due to defects in blood coagulation.
• There are two naturally occurring forms of vitamin K: vitamin K1 (phylloquinone) derived from plants, and vitamin K2 (menaquinones) produced by microorganisms.
• Vitamin K is also synthesized by microorganisms in the intestinal tract.
• Excellent sources of vitamin K include cabbage, cauliflower, spinach, and other green vegetables.
• Vitamin K is absorbed only in the presence of bile salts and is transported to the liver in the form of chylomicrons, where it is stored.
• Vitamin K plays a crucial role in blood coagulation, activating blood clotting factors (prothrombin, factor VII, IX, and X) through vitamin K-dependent carboxylation reactions.
• Vitamin K is also required for the carboxylation of glutamic acid residues of osteocalcin, a Ca2+ binding protein present in bone.
• Vitamin K deficiency is associated with hemorrhagic disease, characterized by increased clotting time and uncontrolled hemorrhages on minor injuries.

Vitamin K Deficiency

• Vitamin K deficiency is found in patients with liver disease and biliary obstruction, newborn infants, and individuals with fat malabsorption.
• Deficiency can also occur following antibiotic therapy that sterilizes the gut.

Vitamin E (Tocopherol)

• Vitamin E consists of eight naturally occurring tocopherols, with α-tocopherol being the most active form.
• The major dietary sources of vitamin E are fats and oils, with germ oil, corn oil, fish oil, and eggs being the richest sources.
• Vitamin E is absorbed from the intestine together with dietary lipid and is incorporated into chylomicrons, then delivered to the liver.
• The liver exports vitamin E into very low-density lipoprotein (VLDL) to target cells, where it is distributed to areas requiring antioxidant activity.
• The major site of vitamin E storage is in adipose tissue.