NUTN 302: Nutrients and Their Metabolism - Vitamins PDF

5/26/2024 NUTN 302: Nutrients and their metabolism - Vitamins...

5/26/2024 NUTN 302: Nutrients and their metabolism - Vitamins 1 1 Course outline  Explain the concept of vitamins  Distinguish between different classes of vitamins  Give food sources for different vitamins  Describe the major functions and metabolic pathways of vitamins in the body  Discuss the body’s requirements for vitamins  Recognize deficiency symptoms of different vitamins  Describe the toxicity potential and effects of different vitamins 2 2 Lecture 1 outcome  Explain the concept of vitamins ◦ Define vitamins? ◦ Discuss vitamine versus vitamin ◦ Explain the operating definition of a Vitamin ◦ Explain the vitamin caveat ◦ List the recognized vitamins ◦ Explain how vitamins differ from carbohydrates, proteins and fats. 3 3 1  5/26/2024 Vitamins (1) Among the nutrients required for the many essential physiologic functions. Serve no structural functions. Catabolism does not provide significant energy. Their various uses each tend to be highly specific hence required in only small amounts in the diet The common food forms of most vitamins require some metabolic activation to their functional forms. 4 4 The term “Vitamin” is physiological term rather than a chemical term, expresses a certain physiological activity Vitamins (2) that is related to the chemical substances responsible for this activity Classified as vitamins by empirical or legislative definitions than by common biochemical functions 5 5 Beginning of 20th Century, growth failure of rats fed only fats, protein, carbohydrates, and mineral salts could be reversed by addition of Vitamin or small amount of milk. Vitamine? (1) Milk was suggested to contain one or more “accessory growth factors” – essential nutrients present in small amounts and needed for normal growth and development 6 6 2  5/26/2024 Polish biochemist Casimir Funk coined vitamine, from the Latin vita for “life” and amine, because the first “accessory growth factor” isolated was an amine Vitamin or Vitamine? (2) Not all of the “accessory growth factors” were found to be amines: name has been retained– loss of the final“-e” to avoid chemical confusion Hence Vitamin 7 7 Organic compound distinct from proteins, fats, and carbohydrates. Natural component of foods in which it is usually present in minute amounts. An operating Essential, also usually in minute amount, for normal definition of a physiological function (i.e., maintenance, growth, Vitamin (1) development, etc.) Absence or underutilization of a vitamin causes specific deficiency syndrome Not synthesized by the host in amounts adequate to meet normal physiological needs 8 8 Distinguishes vitamins from other nutrients, eg protein, fat, carbohydrate, “ash”, and water Indicates need for vitamins for various normal physiological functions. Operating definition: usefulness Points out that deficiency syndromes are specific Recognizes that animals (including humans) depend on vitamins for survival 9 9 3  5/26/2024 Operating definition: limitations  Most animals can synthesize ascorbic acid -- except a few (e.g., guinea pig and humans) lacking l-gulonolactone oxidase, for whom ascorbic acid can properly be called vitamin C.  Exposure to modest amounts of sunlight enable one to produce cholecalciferol (Vit D), except those in indoor confinement.  All animal species can synthesize nicotinic acid mononucleotide (NMN) from tryptophan, except those for which this conversion is inefficient (e.g., cat, fishes) or fed low tryptophan require niacin. 10 10 The vitamin caveat Some compounds are vitamins for one species and not another. Some compounds are vitamins only under specific dietary or environmental conditions 11 11 Criteria for Vitamins  Cannot be synthesized in ample amounts in the body  Chronic deficiency is likely to cause physical symptoms  Symptoms will disappear once the vitamin level in the body is restored ◦ Deficiency can cause permanent damage  13 compounds meet the above criteria 12 4  5/26/2024 Recognized Vitamins (1)  13 substances or groups of substances are generally recognized as vitamins ◦ A vitamin may be a family of chemically related compounds. ◦ Eg Vit E is analogs of tocol or tocotrienol ◦ Members of the same vitamin family are called vitamers ◦ A substance (precursor) may be metabolized in order to yield the active form of a vitamin ◦ A precursor of an actual vitamin is called a provitamin.  Other substances have been proposed but not recognized as vitamins (eg. choline, carnitine, lipoic acid, etc.) 13 13 1) Vitamin A (retinols and beta carotene) 2) Vitamin B1 (thiamin) 3) Vitamin B2 (riboflavin) 4) Vitamin B3 (niacin and niacinamide) 5) Vitamin B6 (pyridoxine and related congeners), 6) Vitamin B12 (cobalamins), Recognized 7) Biotin Vitamins (2) 8) Folate 9) Pantothenate, 10) Vitamin C (ascorbate) 11) Vitamin D (calciferols) 12) Vitamin E (tocopherols) 13) Vitamin K (phylloquinones and menaquinones) 14 14 Structurally Vitamins made up of individual units (not linked together) How Vitamins differ from Function carbohydrates, Do not yield energy proteins and Assist enzymes to release energy from CHO, fats proteins and fats Food content Amount ingested from food and amounts required are measured in micrograms 15 15 5  5/26/2024 Lecture 2: Outline  List substances (factors) sometimes referred to as vitamins  Explain vitamers  Describe provitamins and preformed Vitamins  Distinguish between classed vitamins according to their solubilities  Explain vitamin solubility 16 16 Other factors sometimes called vitamins  Choline ◦ Component of the neurotransmitter acetylcholine and the membrane structural component phosphatidylcholine  p-Aminobenzoic acid ◦ Essential growth factor for several microbes, in which it functions as a provitamin of folic acid.  Myo-Inositol ◦ Component of phosphatidylinositol  Lipoic acid ◦ Cofactor in oxidative decarboxylation of α-keto acids  Carnitine ◦ Essential for transport of fatty acyl-CoA from cytoplasm to mitochondria for β oxidation 17 17 Vitamers  Vitamers are different forms of a particular vitamin  Group of chemical compounds, usually related structurally to one another, responsible for the physiological activity of a vitamin 18 18 6  5/26/2024 The vitamins: their vitamers, provitamins (1) Vitamin Vitamers Provitamins Vitamin A Retinol; Retinal; Retinoic acid β-Carotene; Cryptoxanthin Vitamin D Cholecalciferol (D3); Ergocalciferol (D2) Vitamin E α-Tocopherol; β-Tocopherol; γ- Tocopherol; α-tocotrienol Vitamin K Phylloquinones (K1); Menaquinones (K2); Menadione (K3) Vitamin C Ascorbic acid; Dehydroascorbic acid 19 19 The vitamins: their vitamers, provitamins (2) Vitamin Vitamers Provitamins Vitamin B1 Thiamin Vitamin B2 Riboflavin Niacin Nicotinic acid; Nicotinamide Vitamin B6 Pyridoxine (pyridoxol); Pyridoxal; Pyridoxamine Folic acid Folic acid; Polyglutamyl folacins 20 20 The vitamins: their vitamers, provitamins (3) Vitamin Vitamers Provitamins Biotin Biotin Pantothenic Pantothenic acid acid Vitamin B12 Cobalamin 21 21 7  5/26/2024 Provitamins and Preformed Vitamins  Provitamins ◦Substances found in foods that are not in a form directly usable by the body ◦Converted to the active form once absorbed  Preformed vitamins ◦Vitamins found in foods in their active form 22 Classifying the vitamins according to their solubility (1) 1) Fat soluble Have predominantly aromatic and aliphatic characters 2) Water-soluble Tend to have one or more polar or ionizable groups (carboxyl, keto, hydroxyl, amino, or phosphate) 23 23 Classifying the vitamins according to their solubility (2)  Fat soluble Water-soluble 1) Vitamin A (retinols and beta 1) Vitamin B1 (thiamin) carotene) 2) Vitamin B2 (riboflavin) 2) Vitamin D (calciferols) 3) Vitamin B3 (niacin and 3) Vitamin E (tocopherols) niacinamide) 4) Vitamin K (phylloquinones and 4) Vitamin B6 (pyridoxine and related menaquinones congeners), 5) Vitamin B12 (cobalamins), 6) Biotin 7) Folate 8) Pantothenate, 9) Vitamin C (ascorbate) 24 24 8  5/26/2024 Vitamin solubility (1)  Solubility influences a vitamin’s ◦Digestion ◦Absorption ◦Transportation ◦Storage ◦Excretion 25 Vitamin stability  Water-soluble vitamins can be destroyed by ◦ Exposure to air ◦ Exposure to ultraviolet light ◦ Water ◦ Changes in pH ◦ Heat ◦ Food preparation techniques  Fat-soluble vitamins tend to be more stable 26 9