Physiological Functions of Common Vitamins and Related Deficiencies

Vitamin	Chief Functions	Results of Deficiency	Characteristics	Good Sources
Vitamin A
Retinol (animal source) Carotene Beta-carotene	Essential for maintaining the integrity of epithelial membranes Helps maintain resistance to infections Necessary for the formation of rhodopsin and prevention of night blindness Necessary for proper bone growth Facilitates RNA formation from DNA Thought to be cancer preventive because of antioxidant properties associated with control of free radical damage to DNA and cell membranes	*Mild:* Retarded growth Increased susceptibility to infection Abnormal function of gastrointestinal, genitourinary, and respiratory tracts due to altered epithelial membranes Skin dries, shrivels, thickens; sometimes pustule formation Night blindness *Severe:* Xerophthalmia, a characteristic eye disease, and other local infections	Fat soluble^* Not destroyed by ordinary cooking temperatures is destroyed by high temperatures when oxygen is present Marked capacity for storage in the liver NOTE: Excessive intake of carotene, from which vitamin A is formed, may produce yellow discoloration of the skin ( carotenemia ); excessive vitamin A intake causes symptoms similar to those of deficiency conditions	Liver Animal fats: Butter Cheese Cream Egg yolk Whole milk Fish liver oil Liver Vegetables: Green leafy, especially escarole, kale, parsley Yellow, especially carrots Artificial: Concentrates in several forms Irradiated fish oils
Vitamin B₆
Pyridoxine Pyridoxal Pyridoxamine	Used in hemoglobin synthesis Essential for metabolism of tryptophan to niacin Needed for utilization of certain other amino acids	Anemias Depressed immunity Dermatitis around eyes and mouth Neuritis Anorexia, nausea, and vomiting	Soluble in water and alcohol Rapidly inactivated in presence of heat, sunlight, or air	Meats Cereal grains Some fruits Nuts
Vitamin B₁₂
Cyanocobalamin Hydroxycobalamin	Necessary for myelin synthesis Essential for normal development of red blood cells Associated with folate metabolism	Pernicious anemia Neurological disorders	Soluble in water or alcohol Unstable in hot alkaline or acid solutions	Found only in animal products (e.g., meats, eggs, dairy products) Most of vitamin B₁₂ required by humans is synthesized by intestinal bacteria; can also be recycled
Vitamin C
Ascorbic acid	Essential to formation of intracellular cement substances in a variety of tissues, including skin, dentin, cartilage, and bone matrix Important in healing of wounds and bone fractures Prevents scurvy Facilitates absorption of iron Protects folate Antioxidant Promotes capillary permeability	*Mild:* Lowered resistance to infections Joint tenderness Susceptibility to dental caries, pyorrhea, and bleeding gums Delayed wound healing Bruising *Severe:* Hemorrhage Anemia Scurvy NOTE: Many drugs affect availability	Soluble in water Easily destroyed by oxidation; heat hastens the process Lost in cooking, particularly if water in which food was cooked is discarded; loss is greater if cooked in iron or copper utensils Quick-frozen foods lose little of their vitamin C Stored in the body to a limited extent	Abundant in most fresh fruits and vegetables, especially citrus fruit and juices, tomato and orange Artificial: Ascorbic acid Cevitamic acid
Vitamin D
Calciferol Ergocalciferol Cholecalciferol Calcitriol Antirachitic factor	Hormone-like regulation of calcium and phosphorus metabolism by promotion of: Gastrointestinal absorption Bone and tooth mineralization Renal reabsorption Skeletal reserves Antirachitic	*Mild:* Interferes with utilization of calcium and phosphorus in bone and tooth formation Irritability Weakness *Severe:* Rickets in young children Osteomalacia in adults	Soluble in fats and organic solvents^* Relatively stable under refrigeration Stored in liver Often associated with vitamin A	Formed in the skin by exposure to sunlight Fortified milk and dairy products Egg yolk Fish liver oils Fish having fat distributed through the flesh, salmon, tuna, herring sardines Liver Oysters Artifically prepared forms
Vitamin E
Alpha-tocopherol Beta-tocopherol Gamma-tocopherol	Important antioxidant that: Prevents red blood cell hemolysis Protects vitamin A and unsaturated fatty acids from oxidation Promotes cell membrane integrity Improves immune response May protect against cancer	Red blood cell resistance to rupture is decreased, but deficiency seldom occurs except in premature infants and people with chronic fat malabsorption	Soluble in fat^* Stable to heat in absence of oxygen and ultraviolet light Unstable under freezing and processing	Vegetable oils Margarine Whole-grain or fortified cereals Wheat germ Green leafy vegetables
Folate
Folacin Folic acid	Essential for normal functioning of hematopoietic system Important coenzyme for RNA and DNA synthesis Important in fetal development Functions interrelated with those of vitamin B₁₂	Anemia NOTE: Neural tube defects (e.g., spina bifida ) are associated with maternal deficiency; alcohol and contraceptives interfere with absorption	Slightly soluble in water Easily destroyed by heat in presence of acid Decreases when food is stored at room temperature NOTE: A large dose may prevent appearance of anemia in a case of pernicious anemia but still permit neurological symptoms to develop	Liver Eggs Fish Green leafy vegetables Asparagus Peas, beans, legumes Nuts, seeds, wheat germ Avocado Some fruits
Vitamin K
Menadione Phylloquinone Menaquinone	Promotes synthesis of clotting factors	Prolonged clotting time, resulting in bleeding NOTE: Seldom occurs in the absence of anticoagulant drugs; in addition to food sources, intestinal bacteria manufacture approximately half the body’s requirement Fat malabsorption can cause deficiency Synthetic form (menadione) does not depend on fat absorption	Soluble in fat^* Stable to heat	Green leafy vegetables Meats Dairy products Intestinal bacteria
Niacin
Nicotinic acid Nicotinamide Antipellagra vitamin	As the component of two important enzymes, it is important in glycolysis, tissue respiration, fat synthesis, and cellular energy production Nicotinic acid, but not nicotinamide, causes vasodilation and flushing Prevents pellagra	Pellagra Gastrointestinal disturbances Mental disturbances NOTE: Associated with alcoholism	Soluble in hot water and alcohol Not destroyed by heat, light, air, or alkali Not destroyed in ordinary cooking	Milk Eggs Meats Legumes Enriched foods Whole-grain cereals Nuts NOTE: Also formed in the body from dietary tryptophan (amino acid)
Riboflavin
Vitamin B₂	Important as coenzyme in cellular oxidation Essential to normal growth Participates in light adaptation Vital to protein metabolism Associated with niacin and vitamin B₆ functions	Impaired growth Lassitude and weakness Cheilosis Glossitis Dermatitis Anemia Photophobia Cataracts	Water soluble Alcohol soluble Not destroyed by heat in cooking unless with alkali Unstable in light, especially in presence of alkali	Milk and milk products Enriched foods Whole-grain breads and cereals Liver Meats Eggs
Thiamine
Vitamin B₁	Important role in carbohydrate metabolism Essential for maintenance of normal appetite Essential for normal functioning of nervous tissue Coenzyme for cellular energy production	*Mild:* Loss of appetite Impaired metabolism of starches and sugars Emaciation Irritability *Severe:* Various nervous disorders Loss of coordinating power of muscles Beriberi Paralysis in humans	Soluble in water Not readily destroyed by ordinary cooking temperatures Destroyed by exposure to heat, alkali, or sulfites Not stored in body NOTE: Deficiency is often associated with alcoholism	Widely distributed in plant and animal tissues but seldom occurs in high concentration, except in brewer’s yeast Enriched or whole-grain cereals Pork Peas, beans Nuts Artificial: Concentrates from yeast Rice polishings Wheat germ

^* Vitamins A, D, E, and K are available in water-soluble forms and are used in children with cystic fibrosis and celiac disease.

Adapted from Venes, D (ed): Taber’s Cyclopedic Medical Dictionary, ed 20. FA Davis, Philadelphia, 2005.

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Table 9-5