Fat Soluble Vitamins 3: Vitamins K and E

Lecture 43: Fat Soluble Vitamins 3 - Vitamins K and E

• Specific Objectives: Students will understand the importance of vitamins K and E in the body, explain symptoms of vitamin K deficiency in newborns, and discuss toxicity symptoms of both vitamins.

Vitamin K

• Forms: Vitamin K exists in various forms. Phylloquinone (vitamin K1) is found in plants, and menaquinone (vitamin K2) is found in intestinal bacteria. A synthetic form of vitamin K is menadione.

• Function: Vitamin K is crucial for the hepatic synthesis of prothrombin and other blood clotting factors (II, VII, IX, and X). It works by carboxylating glutamic acid residues into gamma-carboxyglutamate (GLA) residues.

• Inhibition: The formation of GLA is susceptible to inhibition by dicumarol (naturally occurring in spoiled sweet clover) and warfarin (a synthetic vitamin K analog).

• Distribution & Requirement: Vitamin K is present in cabbage, kale, spinach, egg yolks, and liver. The intestinal bacteria also synthesize the vitamin. The RDA for adult males is 120 µg/day, and 90 µg/day for females.

• Clinical Indications: True vitamin K deficiency is uncommon because sufficient amounts are usually produced by gut bacteria or obtained from the diet. A decrease in gut bacterial population (e.g., due to antibiotics) can lead to hypoprothrombinemia, particularly in malnourished individuals, for instance, geriatric patients.

• Newborn Deficiency: Newborns have sterile intestines, so they lack the bacteria needed for vitamin K synthesis. Human milk provides only a small amount of vitamin K, thus newborns are given a single intramuscular dose of vitamin K for prophylaxis against hemorrhagic disease.

• Toxicity: Prolonged use of synthetic vitamin K (menadione) can cause hemolytic anemia and jaundice in infants due to its toxic effect on red blood cell membranes. Thus, this form is no longer used to treat vitamin K deficiency.

Vitamin E

• Forms: Vitamin E consists of eight naturally occurring tocopherols. Alpha-tocopherol is the most active form.

• Function: Vitamin E's primary function is as an antioxidant, preventing the non-enzymatic oxidation of cell components, such as polyunsaturated fatty acids, by molecular oxygen and free radicals.

• Distribution & Requirement: Vegetable oils are good sources of vitamin E. Liver and eggs also contain moderate amounts. The recommended daily allowance (RDA) for alpha-tocopherol is 15 mg for adults. The requirement increases with increased intake of polyunsaturated fatty acids.

• Deficiency: Vitamin E deficiency is mostly seen in premature infants. In adults, it's usually associated with defective lipid absorption or transport. Signs include erythrocyte sensitivity to peroxide and abnormal cellular membranes.

• Toxicity: Vitamin E is the least toxic of the fat-soluble vitamins. No toxicity has been observed in doses up to 300 mg daily. High fruit and vegetable intake correlates with lower chronic disease incidence.

This quiz focuses on the essential roles of vitamins K and E in the body, including their functions, sources, and deficiency symptoms. Students will learn about the significance of these vitamins in blood clotting and discuss potential toxicity effects. Master your understanding of these vital nutrients!