Principles of Biochemistry Volume 3 - A. Lehninger 1985

Selected Aspects of Human Biochemistry
Human Nutrition
Vitamin E or K deficiency in humans is extremely rare.

Because the content of Vitamins E and K in standard diets in the USA significantly exceeds minimum daily requirements, deficiencies of these vitamins are extremely rare. Furthermore, vitamin K can be synthesized by intestinal Bacteria. Vitamins E and K are Fat-soluble vitamins; therefore, their Absorption in the Small Intestine can be impaired under conditions accompanied by pathological changes in Lipid Absorption, particularly in Bile acid secretion disorders. Vitamin E (Fig. 26-22) protects Membrane Lipids from the oxidative degradation of polyunsaturated Fatty acids. A daily intake of 10–30 mg of α-tocopherol is recommended. In large doses, tocopherol is non-toxic; however, there is no evidence that high doses of tocopherol improve complexion or cure Infertility, as some enthusiasts believe.

Vitamin K (Fig. 26-23) is administered to newborns, as well as to patients before and after Liver or Gallbladder surgery, to maintain normal Blood prothrombin levels. Vitamin K deficiency, as mentioned earlier (Section 10.17), impairs the enzymatic carboxylation of specific glutamic acid residues in prothrombin and other Proteins involved in the Blood Coagulation cascade. Very high doses of vitamin K are toxic.