Vitamin
Types, & Facts
vitamin, any of several organic substances that are necessary in small quantities for normal health and growth in higher forms of animal life. Vitamins are distinct in several ways from other biologically important compounds such as proteins, carbohydrates, and lipids. Although these latter substances also are indispensable for proper bodily functions, almost all of them can be synthesized by animals in adequate quantities. Vitamins, on the other hand, generally cannot be synthesized in amounts sufficient to meet bodily needs and therefore must be obtained from the diet or from some synthetic source. For this reason, vitamins are called essential nutrients. Vitamins also differ from the other biological compounds in that relatively small quantities are needed to complete their functions. In general these functions are of a catalytic or regulatory nature, facilitating or controlling vital chemical reactions in the body’s cells. If a vitamin is absent from the diet or is not properly absorbed by the body, a specific deficiency disease may develop.
Vitamins are usually designated by selected letters of the alphabet, as in vitamin D or vitamin C, though they are also designated by chemical names, such as niacin and folic acid. Biochemists traditionally separate them into two groups, the water-soluble vitamins and the fat-soluble vitamins. The common and chemical names of vitamins of both groups, along with their main biological functions and deficiency symptoms, are listed in the table.
vitamin
alternative names/forms
biological function
symptoms of deficiency
Water-soluble
thiamin
vitamin B1
component of a coenzyme in carbohydrate metabolism; supports normal nerve function
impairment of the nerves and heart muscle wasting
riboflavin
vitamin B2
component of coenzymes required for energy production and lipid, vitamin, mineral, and drug metabolism; antioxidant
inflammation of the skin, tongue, and lips; ocular disturbances; nervous symptoms
niacin
nicotinic acid, nicotinamide
component of coenzymes used broadly in cellular metabolism, oxidation of fuel molecules, and fatty acid and steroid synthesis
skin lesions, gastrointestinal disturbances, nervous symptoms
vitamin B6
pyridoxine, pyridoxal, pyridoxamine
component of coenzymes in metabolism of amino acids and other nitrogen-containing compounds; synthesis of hemoglobin, neurotransmitters; regulation of blood glucose levels
dermatitis, mental depression, confusion, convulsions, anemia
folic acid
folate, folacin, pteroylglutamic acid
component of coenzymes in DNA synthesis, metabolism of amino acids; required for cell division, maturation of red blood cells
impaired formation of red blood cells, weakness, irritability, headache, palpitations, inflammation of mouth, neural tube defects in fetus
vitamin B12
cobalamin, cyanocobalamin
cofactor for enzymes in metabolism of amino acids (including folic acid) and fatty acids; required for new cell synthesis, normal blood formation, and neurological function
smoothness of the tongue, gastrointestinal disturbances, nervous symptoms
pantothenic acid
as component of coenzyme A, essential for metabolism of carbohydrate, protein, and fat; cofactor for elongation of fatty acids
weakness, gastrointestinal disturbances, nervous symptoms, fatigue, sleep disturbances, restlessness, nausea
biotin
cofactor in carbohydrate, fatty acid, and amino acid metabolism
dermatitis, hair loss, conjunctivitis, neurological symptoms
vitamin C
ascorbic acid
antioxidant; synthesis of collagen, carnitine, amino acids, and hormones; immune function; enhances absorption of non-heme iron (from plant foods)
swollen and bleeding gums, soreness and stiffness of the joints and lower extremities, bleeding under the skin and in deep tissues, slow wound healing, anemia
Fat-soluble
vitamin A
retinol, retinal, retinoic acid, beta-carotene (plant version)
normal vision, integrity of epithelial cells (mucous membranes and skin), reproduction, embryonic development, growth, immune response
ocular disturbances leading to blindness, growth retardation, dry skin, diarrhea, vulnerability to infection
vitamin D
calciferol, calatriol (1,25-dihydroxy vitamin D1 or vitamin D hormone), cholecalciferol (D3; plant version), ergocalciferol (D2; animal version)
maintenance of blood calcium and phosphorus levels, proper mineralization of bones
defective bone growth in children, soft bones in adults
vitamin E
alpha-tocopherol, tocopherol, tocotrienol
antioxidant; interruption of free radical chain reactions; protection of polyunsaturated fatty acids, cell membranes
peripheral neuropathy, breakdown of red blood cells
vitamin K
phylloquinone, menaquinone, menadione, naphthoquinone
synthesis of proteins involved in blood coagulation and bone metabolism
impaired clotting of the blood and internal bleeding
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