Food Constituents [continued] Micronutrients B-Vitamins The B group of vitamin {water soluble} includes: Thiamine: vitamin B 1, ant beriberi vitamin. Riboflavin: vitamin B 2. Niacin: nicotinic acid, PP factor {pellagra preventing factor}. Folic acid. Cyancobalamin: vitamin B 12. Pyridoxine: vitamin B 6. Biotin Pantothenic acid and others. Sources: Biosynthesis: by intestinal flora and tissues, except B 12 which is only dietary. Dietary Sources: plant and animal foods, except B 12 which is provided by animal foods only. Plant foods: {yeast}, whole-grain cereals, pulses, nuts, green leafy vegetables Animal foods: egg yolk, meat, organ meat. Physiological Role: B-vitamins are coenzymes of many enzymes systems of body metabolism. Thiamine {B 1 } Physiological Role: B 1 is needed for carbohydrate metabolism: thiamine is part of the coenzyme thiamine pyrophosphate {TPP}, which is involved in major decaboxylation of enzyme cocarboxylase. Deficiency: causes impaired carbohydrate metabolism, clinically manifested as: beriberi which is classified as dry beriberi involves the nerves { peripheral neuropathy } and wet beriberi which involve myocardium. Wernicke- Korsakoff syndrome in chronic alcoholics, ( encephalopathy and psychosis ) Recommended daily allowance: Adult male 1.5 mg. ١
Increased during pregnancy and lactation. Increased whenever dietary carbohydrate is increased to provide more energy, according to energy need. Riboflavin {B2} B2 has fluorescent yellow-green color. Sources : Milk is the richest source, hence also named "lactofavin". eggs Liver &kidney yeast extracts Function : promotion of normal growth assisting of synthesis of steroids, glycogen maintenance of mucous membranes, skin, eyes, and the nervous system aiding Fe absorption Deficiency: shows mouth and eye manifestations. Mouth: angular stomatitis {information and fissures of mouth angles}, cheilosis, glossitis, and nasolabial dermatitis. Eyes: circumcorneal vascularization, with lacrimation, photophobia, irritation and sandy feeling. Recommended daily allowance: Adult male 1.7mg.Increased during pregnancy and lactation. Sources: dietary and biosynthesis. Niacin ( nicotinamide, nicotinic acid ) Biosynthesis: animal protein foods provide the essential amino acid tryptophan which is converted, by biosynthesis, into niacin, and so tryptophan is considered "niacin precursor". Niacin deficiency: causes pellagra which is characterized by: Dermatitis Diarrhea Dementia. ٢
Recommended daily allowance: Adult male nearly 20 mg of total niacin, that depends on dietary niacin and tryptophan. It is increased during pregnancy and lactation. Folic acid Physiological Role: Folic acid is needed, together with B 12, for development of red blood cells in the bone marrow. Folates are essential for the synthesis of DNA and RNA Deficiency: causes "megaloblastic {macrocytic} anaemia", where development of RBCs in the bone marrow stops at megaloblast stage Vitamin B 12 Vitamin B 12, ( cobalamin is the natural form, and cyanocobalamin is the commercially available one ), is water-soluble, crystalline red cobalt-containing compound. It is absorbed in the small intestine, it needs an intrinsic factor secreted by healthy stomach mucosa. The liver stores enough vitamin B 12 for 3 years Sources: of B 12 differ from other B-vitamins by being: Only dietary, no biosynthesis. Provided by animal foods only, especially liver, kidney, meat and fish. Physiological Role: B 12 is involved in Synthesis of nucleoproteins. Formation of red cells in the bone marrow. Normal myelination of nerves. Deficiency: Causes pernicious anemia ( megaloblastic ), and or nervous manifestations. Deficiency May be primary or secondary. Primary deficiency: dietary, with plant or largely plant diet. Secondary deficiency: When intrinsic factor is lacking, and so dietary B 12 is not absorbed in small intestine: with degeneration of gastric mucosa, or gastrectomy. The intestinal parasite "Diphyllobothrium latum" consumes B 12. ٣
Recommended daily allowance: 2 micrograms for adults. Intake increased during pregnancy and lactation. Vitamin B 6 There are three naturally occurring forms of Vit B6, pyridoxine, pyrridoxal, and pyridoxamine Physiologic Role: B 6 is converted to the coenzymes pyridoxal 5- phosphate which is involved in amino acid metabolism,. It is included in porphyrin synthesis including heamoglobin. B6 is also involved in the conversion of glycogen to glucose in muscles, the conversion of tryptophan to niacin Food sources: Meat Wholegrain cereals, and fortified cereals Bananas Nuts Deficiency : lead to lesions of the lips and corners of the mouth and inflammation of the tongue. Vit B6 deficiency is usually associated with other vitamin deficiency. Biotin Biotin is made by bacteria and yeasts. biotin is obtained from the diet and synthesized by endogenous bacteria in the colon. Function : biotin is a coenzyme for several carboxylases involved in fatty acid synthesis and metabolism, gluconeogenesis and the metabolism of amino acids Food sources : Liver and kidney Milk Eggs Diary products Deficiency: is rare, it is possible to induce biotin deficiency by ingestion of large amounts of raw egg white, since it contain protein avidin which binds biotin and prevents absorption. the effect is prevented by heating the egg. ٤
Vitamin C {Ascorbic Acid} Sources: Plant foods, while animal foods, including milk, are poor sources. Citrus fruits {and their fresh juice}, jauva and green pepper: the richest sources. Cauliflower, cabbage, tomatoes, sprouting beans. Physiological Role: Vit C is a powerful reducing agent ( antioxidant ) and is essential for many oxidation - reduction reactions Vit C is required for the synthesis of collagen, the main protein in connective tissue and therefore it is essential for the maintenance of muscles, tendons, arteries, bone, skin,. It is essential for the normal functioning of enzymes involved in collagen synthesis Facilitates absorption of iron in the intestine,when consumed in the same meal. Plays a role in amino acid metabolism. Various peptide hormones and releasing factors require activation by Vit C dependent enzyme The hydroxylation of dopamine to the neurotransmitter noradrenaline require vitamin C Deficiency: Scurvy is the clinical syndrome of deficiency. Scurvy is characterized by bleeding anywhere in the body, specially the gums, skin and mucous membranes, and near joints and bones, due to deficient formation of intercellular cement substance which is responsible for normal integrity of capillary walls. Recommended daily allowance: 60 mg for adults, and more during pregnancy and lactation. ` ٥