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Chapter 9

Chapter 9. The Fat Soluble Vitamins. “If a little is good, then more must be better” →Χ *$17 billion/yr in mineral & vit. Supplements in the USA *↑↑↑Vit. → Extra energy, protection from DZ., & prolonged youth? *Plants syn. all the vit. they need. *Animals vary in their ability to syn. vit.

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Chapter 9

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  1. Chapter 9 The Fat Soluble Vitamins

  2. “If a little is good, then more must be better” →Χ *$17 billion/yr in mineral & vit. Supplements in the USA *↑↑↑Vit. → Extra energy, protection from DZ., & prolonged youth? *Plants syn. all the vit. they need. *Animals vary in their ability to syn. vit.

  3. I. Vitamins: Vital Dietary Components *Definition: Essential organic substances needed in small amounts in the diet for normal function, growth & maintenance of body tissues.

  4. *Vitamins→ no energy, but some can facilitate energy-yielding chemical reactions. *Fat-soluble vit.: A, D, E, K *Water-soluble vit.: B vitamins & C

  5. *Indispensable in human diets, Exception: Vit. D, Niacin, Vit. K & biotin. *Substance to be classified as a Vitamin: 1. The body is unable to synthesize enough of the compound to maintain health. 2. absence →deficient signs & symptoms, quickly cured when the substance is re-supplied.

  6. *As pharmacological agents- (1) Megadose of niacin → ↓blood Chol. (selected individuals) (2) Vitamin D analogs→ psoriasis *Isolated from food or synthetic → vitamins same chemical compounds & work equally well in the body. Exceptions: 1.Vit. E, Folate. 2. Some vit. exist in several related forms that differ in chemical or physical properties.

  7. A. Historical perspective on the vitamin 1.Treated night blindness with topical applications of liver extracts. 2.Scurvy was common among sailors 3.Identification of various vitamins → related deficiencies were dramatically cured

  8. 4. Vitamins were named alphabetically: A, B, C, D……….. 5.It took some time to uncover the true nature of the various vitamins. 6.  We can be relatively confident that the vitamins needed by humans have been discovered. Ex.TPN (iv)

  9. B. Storage of Vitamins in the Body 1. The fat-soluble vitamins are not readily excreted from the body. (Exception: Vit. K) 2. The water-soluble vitamins are generally lost from the body quite rapidly. (Exceptions: Vit. B6 &12)

  10. C.Vitamin Toxicity 1.Some fat-soluble vitamins can easily accumulate in the body and cause toxic effects. (Ex. Toxicities of vitamin A & D are the most frequently observed.) 2.Megadose of water-soluble vitamins are also toxic

  11. D.Malabsorption of Vitamins - If absorption of a vitamin is defective, a person must consume larger amounts of it or likely to develop def. -Fat malabsorption is associated with malabsorption of the fat- soluble vitamins - Alcohol abuse & GI diseases/B vitamins

  12. E. Preservation of Vitamins in Foods *Improper storage and excessive cooking →↓Vit. B-1, Vit. C *Heat, light, exposure to the air, cooking in water, and alkalinity are all factors that can destroy vitamins. *If the food is not eaten within a few days, freezing is the best way to retain nutrients

  13. II. Fat-Soluble Vitamins A.Absorption of the Fat-soluble Vitamins 1.Fat-soluble vitamins → lipid like mol. ∴absorbed along with dietary fat, and depends on fat digestion (bile salts & lipase) ~ 40-90 % vitamin ingested (in a typical amounts) are absorbed. (Fig 9-1) 2. Absorption efficiency ↓with intake ↑

  14. B. Distribution of the Fat-soluble Vitamins Fat abs.→chylomicron →TG ↘remnant. fat-sol. Vitamins → liver→→ →→ →→ →→cells & tissues blood lipoprot. - DZs. or medications (Ex. orlistat ) ↓fat absorption → ↓fat-soluble vitamin absorption

  15. III. Vitamin A 1. Vitamin A def. constitutes one of the major public health problems in developing countries. 2. Vitamin A def. is the leading cause of non-accidental blindness. (worldwide) *Children in Africa, Asia and South America

  16. 3. Vit. A structure: Ring + F.A. tail (p.301) 4.Preformed Vit. A: Retinoids: retinal (CHO), retinol (- CH2OH) and retinoic acid (- COOH), cis or trans form (p.300) 5.Provitamin A: Carotinoids –, Ex.: β- carotene, α-carotene, lutein, lycopene, zeaxanthin, β-cryptoxanthin (converted to retinol or retinal)

  17. A. Absorption, transport and metabolism 1. Absorption of preformed vit. A or provitamin A varies from 90% - 3%. depending on the amount of fat. Vitamin A in foods (1) Animal foods - retinol or retinyl ester (retinol + F.A.) (2) Plant foods – carotenoids

  18. Fig 9-1 Digestion and absorption of vitamins - retinyl ester (thru bile and lipase) → retinol + F.A., 90% retinol then absorbed. Form new retinyl ester in the intestinal cells. • Carotenoids are absorbed intact → enzymatically split to retinal in intestinal cell → retinol → retinyl ester • or, absorbed intact carotenoids→ blood stream.

  19. 2. Storage and Transport of Vitamin A (1) Storage: a. Retinoids: Liver  Cartenoids: Liver & adipose tissue liver contains >90 % Vit. A of body b.Adequate for several months

  20. (2) Transport: liver to target cells a. Retinoids: Retinol-binding protein b. Provitamin (carotenoids): VLDL (3) Excretion: only some is lost in the urine.

  21. B. Cellular Retinoid-Binding Proteins (CRBP) - CRBP take up retinoids and hold retinoids and direct them to functional sites within the cell. (transport) - CRBP protect the vitamin from oxidation and enzymatic reactions

  22. C. Retinoid Receptors in the Nucleus - within cell nucleus: RAR and RXR - retinoid/RAR or RXR complex bind to DNA to regulate the activity of retinoid-responsive genes on DNA regulate gene expression → formation mRNA → protein synthesis (Fig. 9-3)

  23. C. Functions of Vitamin A 1.Vision a. Fig. 9-4 vision cycle Retina: (1)Cones – bright light, color images (2)Rods – dim light, black-white images b. Various cell types in the retina, cornea, and epithelium of the eye depend on the presence of retinoic acid for maintaining structural integrity.

  24. 2.Growth and Differentiation of Cells - all-trans retinoic acid and 9-cis-retionic acid→ activate RAR and RXR→code for a variety of structural proteins (Fig. 9-2) - Retinoic acid is also necessary for the production, the structure, and the normal function of epithelial cells. R.A. is also essential in the formation and maintenance of mucus-forming cells. - Retinoic Acid – used for wrinkle

  25. 3. Immunity - Vit. A def. →vulnerable to infections - Specific immunity: cell-mediated and antibody-mediated response, such as macrophage and natural killer cell activity and growth and differentiation of B-lymphocytes • Non-Specific immunity: insufficient mucus production in the eyes, intestinal tract, and lungs, deterioration of many types of cells.

  26. D. Vitamin A Analogs for Acne *Tretinoin (Retin-A): Analog form of vitamin A, acne medication, topical treatment, ↓sebum secretion. *Accutane (13-cis retinoic acid)- acne medication, oral *Acintretin – treat severe psosiasis *** fetal malformations (use during Prg.

  27. E. Possible Carotenoid functions 1. Heart Disease Prevention *Carotenoids: antioxidants *Recommendation: at least 5 servings fruits and veg./day 2. Cancer Prevention - ↓ various cancers in animal studies, but not shown in human study. - Retinoids influence cell differentiation, inhibition cell proliferation & ↑apoptosis

  28. 3. Lycopene protects against prostate cancer (antioxidant ) 4. Age-related macular degeneration (Fig. 9-5): macular contains lutein and zeaxanthin (carotenoids) (↑er carotenoids in the diets ↓ er incidence of macular degeneration) *Megadose vitamin A supplements to ↓cancer risk is currently not advised (∵toxicity)

  29. F. Vitamin A in Foods (p.305) - Preformed vit. A: liver, fish oils, fortified milk, and eggs - Provitamin A: carotenoids in dark green & yellow-orange vegetables & some fruit

  30. 1. *Retinol Activity Equivalent (RAE) 1 RAE = 1μg all-trans retinol = 12μg all-trans β-carotene = 24μg other carotenoids Table 9-1 (p.306) 2. Calculating Retinol activity equivalents 1 RE (or 3.3 IU) = 1RAE Waiting for all the food tables to be updated

  31. G. Vitamin A Needs • *RDA for Vitamin A • Adult: ♂: 900 RAE • ♀: 700 RAE • - Actual intake: meet RDAs • - Liver reserves of vitamin A are • 3 – 5X >needed for good health

  32. H. Vitamin A Deficiency Diseases - Preschool children who do not eat enough veg. - Urban poor, the elderly, people w/ alcoholism or liver disease, children and adult w/ severe fat malabsorption syndromes, cystic fibrosis, AIDS etc.

  33. *Night Blindness *Conjunctival xerosis: abnormal dryness of the conjunctiva of the eye *Bitot’s spot: dry out of the eye and appearance of hardened epithelial cells *Xerophthalmia: → blindness *Follicular hyperkeratosis: keratin accumulates around hair follicles Fig 9-6

  34. I. Upper Level for Vitamin A * Vitamin A Toxicity “ Hypervitaminosis A”: long-term supplement 2 – 4X RDA Fig 9-7 UL: 3000 μg

  35. - 3 kinds of Vitamin A toxicity: a. Acute – GI upset, headache, blurred vision, muscular in-coordination, death b. Chronic – wide range of signs and symptoms

  36. c. Teratogenic – birth defect • * animal study: Accutane causes spontaneous abortion and birth defects • * Pregnant women taking Accutane: offspring show congenital malformations of the head.

  37. *Consuming huge amount of carotenoids – relatively non-toxic, ∵conversion and absorption

  38. *Hypercarotenemia: yellow orange color skin (appears to have jaundice, but sclerae are white and liver is not enlarged) *Lycopenodermia: excessive intake of foods rich in lycopene, A deep orange discoloration.

  39. *Expert Opinion Carotinoids and Human Health: Beyond Conversion to Vitamin A a. Antioxidants: In vitro: trap free radicals In vivo: unknow b. Carotenoids may decrease the risk of cataracts and macular degeneration in the eye, some cancers, some CVD. Clinical trials?

  40. *Hundreds of studies show that diets rich in fruits and vegetables are ass. w/↓ risk of cancer and other chronic diseases. • *Supplement β-carotene→ X↓lung cancer or heart DZ.

  41. *Many researchers are now convinced that β- carotene supplement offer no protection against cancer

  42. c. Eyesight • Age-related macular degeneration is the leading cause of blindness in American over 65. - Study of 876 subjects: ↑carotenoids (β- carotene, lutein and zeaxanthine) intake, ↓macular degeneration

  43. d. Pharmacological use of Vitamin A *Tretinoin (Retin-A): acne medication, topical treatment, ↓sebum secretion. *Accutane (13-cis retinoic acid)- acne medication, oral *Acintretin – treat severe psosiasis *** fetal malformations (use during Prg.) *All trans retinoic acid for leukemia → side effects

  44. VI. Vitamin D • *Prohormone – converted to active form by enzymes in the liver & kidney

  45. *Amount of sun exposure needed to produce vit. D depends on – skin color, age, time of day, season, and location • *Def. – rickets in children - osteomalacia in adults

  46. A.Vitamin D Formation in the Skin (p.309) Cholesterol → 7-dehydrocholesterol (skin) (Provitamin D) UV ↘(290-315 nm) →→→→→→→→→ →→ cholecalciferol lumisterol↗

  47. B. Absorption and Formation of Vitamin D from Food • - 80% of Vit. D - micelles • - Absorbed vit. D w/ chylomicron →liver • - Def. occurred in persons with fat mal- absorption syndromes.

  48. c. Metabolism, Transport, storage, and Excretion of Vitamin D Fig. 9-8 • - Stored : liver & adipose tissue (25(OH)cholecalciferol) Shortage of Ca →↑PTH →↑ 1, 25(OH)2cholecalciferol • - Activated in liver & kidney

  49. Conversion of Provit. to Active Vitamin D liver cholecalciferol→→25(OH)cholecalciferol →→1,25(OH)2 cholecalciferol (Calcitriol) kidney

  50. Animal foods – cholecalciferol (D3) • Plant foods – liver ergosterol (D2)→→25(OH) ergocalciferol →→→1,25(OH)2 ergocalciferol kidney

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