The most active form of the E vitamins is α-tocopherol, one of the eight naturally occurring tocopherols (Fig. 28.28). Vitamin E serves as an antioxidant, protecting against nonenzymic oxidations, such as the oxidation of LDL and the peroxidation of polyunsaturated FA by O2 and free radicals. Note: Vitamin C regenerates active vitamin E.

A. In terms of distribution and requirements, vegetable oils are abundant sources of vitamin E, while liver and eggs contain moderate amounts. The recommended daily allowance (RDA) for α-tocopherol in adults is 15 mg/day. The vitamin E requirement increases as the intake of polyunsaturated FA increases in order to limit FA peroxidation.

B. Deficiency in vitamin E is usually observed in newborns due to low reserves, although breast milk and formulas provide the vitamin. Very-low-birth-weight infants may be given supplements to prevent the hemolysis and retinopathy associated with vitamin E deficiency. In adults, deficiency is typically associated with defective lipid absorption or transport. Note: Abetalipoproteinemia, which is caused by a defect in the formation of chylomicrons (and VLDL), leads to vitamin E deficiency.

C. While vitamin E is not recommended for the prevention of chronic diseases like CVD or cancer, clinical trials using vitamin E supplementation have consistently yielded disappointing results. For instance, subjects in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study trial who received high doses of vitamin E not only did not experience cardiovascular benefits but also had an increased incidence of stroke. Note: Vitamins E and C are utilized to slow down the progression of age-related macular degeneration.

D. Vitamin E is the least toxic among the fat-soluble vitamins, with no observed toxicity at doses of 300 mg/day (UL = 1,000 mg/day). Populations that consume diets rich in fruits and vegetables tend to have a decreased incidence of certain chronic diseases. However, clinical trials have failed to definitively prove the benefits of supplements such as folic acid, vitamins A, C, or E, or antioxidant combinations in preventing cancer or CVD.

XV. CHAPTER SUMMARY
Figure 28.29 on pp. 396–397 provides a summary of the vitamins.

For Questions 28.1–28.5, match the clinical consequence to the corresponding vitamin deficiency.
8.1. Bleeding - Vitamin K deficiency
8.2. Diarrhea and dermatitis - Niacin deficiency
8.3. Neural tube defects - Folic acid deficiency
8.4. Night blindness (nyctalopia) - Vitamin A deficiency
8.5. Sore, spongy gums and loose teeth - Vitamin C deficiency

Severe vitamin C deficiency, known as scurvy, results in defective connective tissue characterized by sore and spongy gums, loose teeth, capillary fragility, anemia, and fatigue.
The E vitamins consist of eight naturally occurring tocopherols, of which αtocopherol is the most active (Fig. 28.28). Vitamin E functions as an antioxidant in prevention of nonenzymic oxidations (for example, oxidation of LDL (see p.
232) and peroxidation of polyunsaturated FA by O2 and free radicals). [Note: Vitamin C regenerates active vitamin E.]
A. Distribution and requirements
Vegetable oils are rich sources of vitamin E, whereas liver and eggs contain moderate amounts. The RDA for α-tocopherol is 15 mg/day for adults. The vitamin E requirement increases as the intake of polyunsaturated FA increases to limit FA peroxidation.
B. Deficiency
Newborns have low reserves of vitamin E, but breast milk (and formulas) contain the vitamin. Very-low-birth-weight infants may be given supplements to prevent the hemolysis and retinopathy associated with vitamin E deficiency. When observed in adults, deficiency is usually associated with defective lipid absorption or transport. [Note: Abetalipoproteinemia, caused by a defect in the formation of chylomicrons (and VLDL), results in vitamin E deficiency (see p. 231).]
C. Clinical indications for vitamin E
Vitamin E is not recommended for the prevention of chronic disease, such as CVD or cancer. Clinical trials using vitamin E supplementation have been uniformly disappointing. For example, subjects in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study trial who received high doses of vitamin E not only lacked cardiovascular benefit but also had an increased incidence of stroke. [Note: Vitamins E and C are used to slow the progression of age-related macular degeneration.]
D. Toxicity
Vitamin E is the least toxic of the fat-soluble vitamins, and no toxicity has been observed at doses of 300 mg/day (UL = 1,000 mg/day).
Populations consuming diets high in fruits and vegetables show decreased incidence of some chronic diseases. However, clinical trials have failed to show a definitive benefit from supplements of folic acid; vitamins A, C, or E; or antioxidant combinations for the prevention of cancer or CVD.
XV. CHAPTER SUMMARY
The vitamins are summarized in Figure 28.29 on pp. 396–397.
Choose the ONE best answer.
For Questions 28.1–28.5, match the vitamin deficiency to the clinical consequence.
8.1. Bleeding 8.2. Diarrhea and dermatitis 8.3. Neural tube defects 8.4. Night blindness (nyctalopia) 8.5. Sore, spongy gums and loose teeth
Correct answers = H, B, A, C, E. Vitamin K is required for formation of the γcarboxyglutamate residues in several proteins required for blood clotting. Consequently, a deficiency of vitamin K results in a tendency to bleed. Niacin deficiency is characterized by the three Ds: diarrhea, dermatitis, and dementia (and death, a fourth D, if untreated). Folic acid deficiency can result in neural tube defects in the developing fetus. Night blindness is one of the first signs of vitamin A deficiency. Rod cells in the retina detect white and black images and work best in low light, for example, at night. Rhodopsin, the visual pigment of the rod cells, consists of 11-cis retinal bound to the protein opsin. Vitamin C is required for the hydroxylation of proline and lysine during collagen synthesis.
Severe vitamin C deficiency (scurvy) results in defective connective tissue, characterized by sore and spongy gums, loose teeth, capillary fragility, anemia, and fatigue.