Vitamins are a group of organic compounds involved in the regulation (often as components in enzyme systems) of certain metabolic activities such as digestion, respiration, immunity and wound healing. They are organic (carbon-containing) compounds but do not fit the classification of carbohydrate, fat or protein. They are essential for normal metabolism but the body cannot make sufficient quantities to satisfy its needs - hence the need to obtain some from the diet.
The name 'vitamin' is derived from 'vital amine'. As the name suggests they are amines essential for life. Despite the fact that some vitamins are not chemically related to amines, the general term vitamin is applied. A better definition would be an essential organic compound, which is either not made in the body or made in such small quantities that additional supply is needed. Vitamins or their precursors (i.e. the things from which they are made) must therefore be provided by the diet.
An inadequate dietary supply of a vitamin can lead to a deficiency disease or sub-optimal metabolism.
How many vitamins are there?
The 13 substances which are currently recognised as vitamins are the four fat soluble vitamins; (A, D, E and K) and the nine water soluble vitamins; vitamin C, folic acid (folate) and the vitamins commonly referred to as the B complex - thiamine (B1), riboflavin (B2), niacin (nicotinamide, nicotinic acid, B3), pyridoxine (B6), pantothenic acid (B5), vitamin B12 (cyanocobalamin), biotin (vitamin B7).
Choline, inositol and para-aminobenzoic acid are also considered by some to be vitamins of the B complex group.
Water and fat soluble vitamins
Fat soluble vitamins A, D, E and K can be stored in the body whereas the water soluble vitamins; C, folic acid and B complex vitamins are water soluble and the body has limited or no stores. The sources of the various vitamins and their role in the body are shown in tables 1 and 2.
Water-soluble vitaminsClick to open table
|VITAMIN||MEDICAL NAME||SOURCES||INVOLVED IN||DEFICIENCY DISEASES / SYMPTOMS OF DEFICIENCY / LOW STATUS|
|C||Ascorbic Acid||Fresh fruits and vegetables||Wound healing Enzyme processes Essential for normal function of cells||Scurvy|
|Folic acid||Folic acid Folate||Vegetables, meat, fish eggs||Cell division. Synthesis of RNA and DNA.||Diarrhoea, weight loss, infertility, megaloblastic anaemia. Secondary deficiency can arise due to malabsorption, certain drugs and in leukaemia.|
|B1||Thiamin||Cereals, yeast||Carbohydrate metabolism Nervous system||Beri-Beri|
|B2||Riboflavin||Plants, yeast, liver, kidney, milk, cheese, eggs||Enzyme processes||Dermatitis, conjunctivitis, cracking of the corner of the mouth|
|B3||Nicotinamide Niacin Nicotinic acid||Yeast, nuts, liver, kidney, egg yolk||Release of energy from carbohydrates, enzyme processes||Pellagra symptoms include: dermatitis, diarrhoea, dementia|
|B5||Pantothenic acid||Yeast, egg yolks, fresh vegetables, widely available in diet but highly processed foods do not contain it||Metabolism of fats and carbohydrates||Spontaneous deficiency unknown. Burning sensation in feet, depression, vomiting, fatigue, muscle weakness|
|B6||Pyridoxine||Yeast, egg yolks, green vegetables||Protein metabolism, hormone metabolism, conversion of glycogen to glucose in muscles||Convulsions, polyneuritis, skin disease, lesions of lips and corners of mouth, inflammation of tongue|
|B7||Biotin||Liver, kidney, milk, eggs, dairy products||Scaly dermatitis, glossitis, hair loss, anorexia,depression, hypercholesterolemia|
|B12||Cyanocobalamin||Animal foods including meat, fortified breakfast cereals, marmite, vegemite. B12 is also manufactured by intestinal bacteria||Growth - formation of blood cells and nervous tissue. Synthesis of methionine from homocysteine (raised homocysteine levels are linked to cardio vascular disease)||Deficiency most common in malabsorption. Pernicious (megaloblastic) anaemia/neurological problems. Degeneration of brain and nervous tissue including neuropathy|
Fat-soluble vitaminsClick to open table
|VITAMIN||MEDICAL NAME||SOURCES||INVOLVED IN||DEFICIENCY DISEASES / SYMPTOMS|
|A||B-carotene / Retinyl palmitate||Fish oils, meat, liver, butter/spreads/ dairy foods, eggs, green plants e.g. cabbage and spinach||Growth, night vision, maintenance of moist (mucous-secreting) tissues, immunity||Night blindness, blindness, drying of mucous membranes, susceptibility to infections|
|D||Calciferols (Ergocalciferol and cholecalciferol)||Formed in the skin on exposure to sunshine. Fish oil, animal fats, margarine, breakfast cereals, eggs, liver||Needed for absorption of calcium from diet and for deposition of calcium into bones||Rickets (softening of bones) in children, Osteomalacia in adults|
|E||Tocopherol||Fat spreads, cereals, sunflower seeds and oils, safflower oil, corn oil, leaf vegetables, dairy foods, , eggs, nuts, peanut butter||Antioxidant - protects cell membranes and lipoproteins (fatty tissues and cell walls) from damage by free radicals||Unknown in humans.
Muscular and cardiac atrophy have been described in cattle, sheep and pigs
|K||Phylloquinine (K1) and menaquinone (K2)||Made by the bacteria in the gut (K2).
Green plants, e.g. spinach, peas, cabbage, eggs, meat, vegetable oils, dairy products
|Blood clotting||Prolonged bleeding Bruising.
Anticoagulant drugs including warfarin and dicoumarol can cause deficiency