Vitamins A, B Complex and C: characteristic, biochemical action, effects of deficiency & excess

NAMES AND SYNONYMS	CHARACTERISTICS	BIOCHEMICAL ACTION	EFFECTS OF DEFICIENCY	EFFECTS OF EXCESS	SOURCES
VITAMIN A
Retinol (vitamin A1);	Fat-soluble Heat-stable Destroyed oxidation, drying Bile necessary for absorption Sstored in liver Protected by vitamin E	In vision, as retinal, for synthesis of the visual pigments rhodopsin and iodopsin. In growth, reproduction, embryonic and fetal development, bone growth, immune and epithelial functions, via retinoic acid as a ligand for specific nuclear transcription factors, regulating genes involved in many fundamental cellular processes.	nyctalopia; photophobia, xerophthalmia, Bitot spots, conjunctivitis, keratomalacia leading to blindness; faulty epiphyseal bone formation; defective tooth enamel; keratinization of mucous membranes and skin; retarded growth; impaired resistance to infection, anemia, reproductive failure, fetal abnormalities.	anorexia, slow growth, drying and cracking of skin, enlargement of liver and spleen, swelling and pain of long bones, bone fragility, increased intracranial pressure, alopecia, carotenemia; fetal abnormalities	liver, fish liver oils, dairy products, except skim milk; egg yolk, fortified margarines fortified skim milk; Carotenoids from plants: green vegetables, yellow fruits and vegetables/
1 μg retinol = 3.3 IU by vitamin A = 1 RAE.
Provitamins A:the plant pigments α-, β-, and γ-carotenes and cryptoxanthin have partial retinol activity: 12 μg β-carotene, or 24 μg of other provitamin A carotenoids = 1 μg retinol
VITAMIN B COMPLEX
Thiamin:vitamin B1; (antiberiberi vitamin)	water and alcohol soluble; fat-insoluble; stable in slightly acid solution; labile to heat, alkali, sulfites	Component of thiamine pyrophosphate involved in oxidative decarboxylation of α-keto acids, such as pyruvate, and in transketolation reactions	beriberi, fatigue, irritability, anorexia, constipation, headache, insomnia, tachycardia, polyneuritis, cardiac failure, edema, elevated pyruvic acid in blood	None from oral intake	Meat, especially pork; Whole-grain or enriched cereals; Legumes; Nuts, Wheat germ; Liver
Riboflavin:vitamin B2	sparingly soluble in water; sensitive to light and alkali; stable to heat, alkali, oxidation, acid	Constituent of flavoprotein enzymes important in oxidation-reduction reactions: amino acid, fatty acid, and carbohyrate metabolism and cellular respiration	ariboflavinosis, photophobia, blurred vision, burning and itching of eyes, corneal vascularization, poor growth, cheilosis	Not harmful	milk, cheese; whole-grain or enriched grains; meat, fish; eggs; green leafy vegetables; liver and other organ meats
Niacin:nicotinamide;nicotinc acid (antipellagra vitamin)	Water- and alcohol-soluble;stable to acid, alkali, light, heat, oxidation	Constituent of NAD and NADP, coenzymes in numerous oxidation-reduction reactions	Pellagra, Multiple B-vitamin deficiency syndrome, diarrhea, dementia, dermatitis Irritability, convulsions, hypochromic anemia; peripheral neuritis in patients receiving isoniazid; oxaluria	Nicotinic acid (not the amide) is vasodilator; Skin flushing and itching; Hepatopathy	Meat, fish, poultry; whole-grain and enriched cereals; green vegetables; peanuts; liver; also from conversion of trytophan to niacin
Vitamin B6 active forms: pyridoxine, pyridoxal, pyridoxamine	Water-soluble;destroyed by ultraviolet light and by heat	Constituent of coenzymes for decarboxylation, transamination, trans-sulfuration;fatty acid metabolism; heme synthesis; homocysteine metabolism		Sensory neuropathy (from high-dose supplements, not food)	Meat, fish, poultry; whole-grain and fortified cereals; soybeans; nuts; potatoes; noncitrus fruits; liver and kidney
Biotin	Crystallized from yeast; soluble in water	Coenzyme carboxylases; involved in CO2 transfer	Dermatitis, seborrhea; inactivated by avidin in raw egg white	Unknown	Widely distributed in foods; Animal products, yeast, liver
Pantothenic acid	Limited data on stability during cooking and food processing	Component of coenzyme A and acyl carrier protein involved in fatty acid metabolism	Experimentally produced deficiency in humans: irritability, fatigue, gastric complaints, numbness, paresthesias, muscle cramps	Unknown	Widely distributed in foods; beef, poultry, whole grains, liver and kidney, yeast, egg yolks
Folate:folic acid, folacin; a group of related compounds containing pteridine ring, para-amino benzoic acid, and glutamic acid; pteroylglutamic acid	Slightly soluble in water: labile to heat, light, acid	Concerned with formation and metabolism of 1-carbon units; participates in synthesis of purines, pyrimidines, nucleoproteins, homocysteine metabolism	Megaloblastic anemia (infancy, pregnancy) usually secondary to malabsorption disease, glossitis, pharyngeal ulcers, impaired immunity	Unknown	Green vegetables, enriched grain products, oranges and other fruits, legumes, nuts, liver, yeast
Vitamin B12:cyanocobalamin	Slightly soluble in water; stable to heat in neutral solution; labile in acid or alkaline ones; destroyed by light; castle intrinsic factor of the stomach required for absorption	Transfer of 1-carbon units in purine and labile methyl group metabolism; essential for maturation of red blood cells in bone marrow; metabolism of nervous tissue; homocysteine metabolism; Adenosylcobalamin is coenzyme for methylmalonyl coenzyme A mutase	Pernicious anemia due to defect in absorption rather than dietary lack; also secondary to gastrectomy, celiac disease, inflammatory lesions of small bowel, long-term drug therapy (PAS, neomycin); methylmalonic aciduria; homocystinuria	Unknown	Animal foods: muscle and organ meats, fish; eggs; milk; cheese; fortified cereal products; fortified soy products
VITAMIN C
Ascorbic acid, antiscorbutic vitamin	Water-soluble; Easily oxidized, accelerated by heat, light, alkali, oxidative enzymes, traces of copper or iron	As an antioxidant, maintains Fe and Cu ions in reduced state in hydroxylases involved in collagen synthesis, metabolism of cholesterol and neurotransmitters; may be needed to maintain folate in a reduced form; facilitates non-heme Fe absorption and Fe transfer from tansferritin to ferritin	Scurvy: poor wound healing, bleeding gums, petechiae, ecchymoses, follicular hyperkeratosis, arthralgia	Adverse effects usually not serious; May include osmotic diarrhea, other gastrointestinal symptoms; Oxaluria	Citrus fruits, tomatoes, berries, cantaloupe, cabbage, broccoli, cauliflower, spinach, potatoes; cooking has destructive effect

Notes:

• NAD(P): Nicotinamide adenine dinucleotide (phosphate)
• PAS: para-aminosalicylic acid

Reference:
Nelson Textbook of Pediatrics 18th Edition