Fat Soluble Vitamins 3: Vitamins K and E

Study Notes

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.