Vitamins were discovered when it was observed that diets adequate in calories, protein and essential amino acids, fats and minerals failed to maintain health. The term vitamin has now come to refer to any organic dietary constituent necessary for life, health and growth, which does not function by supplying energy.
Early studies of the vitamins emphasized the more obvious pathological changes which occurred when animals were maintained on vitamin-deficient diets. Increased knowledge of the physiologic role of vitamin has enabled attention to be concentrated on the metabolic defects which occur when these substances are lacking, and we may therefore refer to the biochemical changes as well as the anatomic lesions which are characteristic of the various vitamin deficiency states.
Before the chemical structures of the vitamins were known it was customary to identify these substances by letters of the alphabet. This system gradually being replaced by a nomenclature based on the chemical nature of the compound or a description of its source or function.
The vitamins are generally divided into 2 major groups fat-soluble and water-soluble. The fat-soluble vitamins, which are usually found associated with the lipids of natural foods, include vitamins A, D, E, and K. The vitamins of the B complex and vitamin C comprise the water-soluble group.
THE LIST OF FAT-SOLUBLE VITAMINS by function, effects of deficiency, effects of excess, requirements and sources or nutrients as follows:
1. VITAMIN A [RETINOL].
Function: The maintenance of the integrity of epithelial tissues or membranes of respiratory, alimentary, genito-urinary tracts, and in the cornea and conjunctiva are an important function of vitamin A. The specific role of vitamin A in the physiologic normal mechanism of vision. Healthy skin, strong teeth and bones in children, maintaining resistance to infection. It was the identification of vitamins A, C, and E as antioxidants that revolutionized the field and led to the realization of the importance of antioxidants in biochemistry of living organisms.
Effects of deficiency: Xerosis of conjunctiva: Thickening with loss of transparency, infrequently associated with small foam-like plaques called Bitot’s spots. Papular eruptions of pilo-sebaceous follicles: A grater-like feel, which in early stages resembles gooseflesh but, when more fully developed, presents the picture of keratosis pilaris. Xerosis of the skin: Dryness, scale-like and crinkling, In extreme cases resembling alligator skin. Follicular conjunctivitis: Hypertrophy of the follicles, particularly of the lower eyelids. Night blindness. Keratomalacia: Thickening with subsequent ulceration and necrosis of cornea, present only in most severe and advanced of deficiency. Since the lack of vitamin A interferes with the process of ovulation, an adequate dietary supply of vitamin A is necessary for normal process of ovulation and fertility. Treatment: Give vitamin A, 20 000 units twice daily.
Effects of excess: Hypervitaminosis A, this disorder is rare in adults. The minimal toxic adult dose is about 75 000 units daily for 6 months. Clinical findings: Anorexia, loss of weight, hair loss, hyperostosis and periostal elevation of bone, hepato-megaly [enlarged of liver], spleno-megaly [enlarged of spleen], anemia and skin rash. Treatment: Withdraw the medicinal source.
Requirements: The recommended daily allowances [RDA] for adults are 5000 I.U. [or U.S.P. units], during pregnancy and lactation, 6000-8000 I.U.
Sources: It is present in leafy green and yellow fruits and vegetables, whole milk, butter, eggs, fish, or liver oil.
VITAMIN D [CALCIFEROL].
Functions: The vitamins D are sterols formed in the skin by ultraviolet irradiation of plant sterol precursors. Aids in bone and tooth formation. Strong bones; regulation of the absorption of calcium and phosphorus from the digestive tract.
Effects of deficiency: Avitaminosis D is usually due to inadequate dietary intake, lack of sunlight, or absorption defect. Clinical findings: Lack of vitamin D leads to osteomalacia in children [rickets]. In adults: osteomalacia due to calcium loss from bones. Treatment of rickets in children is 3500 units daily are adequate. Adult osteomalacia treatment usual doses is 50 000-100 000 units daily, large doses are necessary to compensate renal loses of phosphate.
Effects of excess: This hypervitaminosis D is usually caused by prolonged ingestion of more than 100 000 units daily. Clinical findings: The manifestations of hyper-calcemia are present and may progress to renal damaged and metastatic calcification. Treatment: Withdraw the medicinal source. Complete recovery will occur if over-treatment is discontinued in time.
Requirements: For children and for women during pregnancy and lactation, 400 units are recommended. The daily allowances for adults are not known.
Sources: Cod liver oil, sardines, herring, salmon, tuna, milk and milk products, liver and eggs. The action of sunlight on the skin allows our body to manufacture vitamin D.
VITAMIN E [TOCOPHEROL]
Function: The most striking characteristic of the vitamin E is their antioxidant property. Polyunsaturated fatty acids are easily attacked by molecular oxygen, resulting in formation of peroxides, the tocopherols prevent this. Normal brain function, formation of red blood cells, maintaining some enzyme, normal cellular structure, protection against pollutants.
Effects of deficiency: Weak muscles and infertility. Heart muscle is affected like skeletal muscle by vitamin E deficiency. In male shows testicular atrophy and may failure of spermatogenesis. In female, ovarian function is normal, but there is partial failure of implantation, and the fertilized ova successfully implanted grow and develop only to a certain stage, at which time the fetuses show generalized hemorrhage, die, and are aborted or resolved. Administration of vitamin E during the first half of gestation permits normal fetal development and parturition. The normal resistance of red blood cells to rupture is reduced in vitamin E deficiency. The dietary liver necrosis is the result of simultaneous lack of selenium and of vitamin E. A lack of one or the other alone produces relatively mild chronic diseases. Treatment: Give vitamin E 100 mg twice daily.
Effects of excess: There is a slight risk of overdose, because vitamin E is fat soluble, and usually limited intake of fat.
Requirements: RDA 10 mg daily.
Sources: Eggs, vegetable oils, nuts, soy-beans, broccoli, sprouts, spinach, whole-wheat products.
VITAMIN K [PHYLLOQUINONE]
Function: The vitamins K are chemical compounds which are necessary for prothrombin synthesis by the liver and so are important in the blood coagulation mechanism.
Effects of deficiency: Avitaminosis K results from liver disease which interferes with synthesis of prothrombin, inadequate bile supply with poor absorption, or ingestion of drugs which depress prothrombin synthesis such as coumarins, salicylates. Bleeding disorders in new born infants and those on blood-thinning medication, Treatment: Give 2-5 mg daily is capable of correcting most deficiency.
Effects of excess: Hypervitaminosis K : Large doses of vitamin K to infants, particularly premature infants, may cause hemolytic anemia, hyper-bilirubinemia, hepatomegaly, and even death. Treatment: Withdraw the medication source.
Requirements: 1-2 mg daily.
Sources: Cabbage, cauliflower, spinach, soybeans, green leafy vegetables, dairy products.