Vitamin A deficiency cause

Vitamin A deficiency is a major problem of children under five in developing countries, being the single most common preventable cause of blindness. Table 2.1 shows the prevalence of vitamin A deficiency in different regions of the world. The increased susceptibility to infection and impairment of immune responses in vitamin A deficiency causes significant childhood mortality. A number of trials of vitamin A supplementation in areas of endemic deficiency show a 20% to 35% reduction in child mortality. 

As has been indicated, Flaning s original interest was in lysozymes, as was Horey s. These turned out to be enzymes present in mucus that act against bacteria, as in the mucus secreted in the nose from the mucous membranes. A parallel discovery was that a vitamin A deficiency caused mucous secretions to cease in the intestine, which was then followed by an invasion of virulent bacteria into intestinal tissues (Macfarlane, 1985, p. 161). An item of peripheral interest is that curare, a poisonous mixture of alkaloids derived from plants of the South American genus Strychnos, acts against tetanus (Macfarlane, 1985, p. 163). 

Nutritional vitamin A deficiency causes xerophthalmia, a progressive disease characterized by night blindness, xerosis (dryness), and keratomalacia (comeal thinning), which may lead to perforation xerophthalmia may be reversed with vitamin A therapy. However, rapid, irreversible blindness ensues once the cornea perforates. Vitamin A also is involved in epithelial differentiation and may have some role in corneal epithelial wound healing. There is no evidence to support using topical vitamin A for keratoconjunctivitis sicca in the absence of a nutritional deficiency. 

Deficiencies of protein, vitamins and minerais affect reproduction indirectiy, through their effects on the generai heaith of animais, but a few have more specific effects on reproduction. Thus, zinc deficiency in maies reduces the production of spermatozoa, and vitamin A deficiency causes congenitai abnormaiities in foetuses. 

The conjugated Tt system fits precisely into an internal cavity of opsin and absorbs light over a broad region of the visible spectrum (400—600 nm). Sources of 11-CM-retinal include vitamin A and (3-carotene. A vitamin A deficiency causes night bUndness, while a diet rich in 3-carotene can improve vision. 

Early workers have Shown that vitamin A deficiency causes a considerable interference in reproduction. Many of their findings, however, are subject to the criticism (see Mason, ) that the diet was not adequately controlled. 

On a vitamin A-deficient diet, mucus-secreting tissues become keratinized. This condition tends to occur in the trachea, the skin, the saUvary glands, the cornea, and the testes. When this occurs in the cornea, it can be followed by blindness. Vitamin A deficiency is the principal cause of blindness in the very young. This problem is particularly acute in the third world (8). 

A deficiency of this vitamin caused by a low dietary intake of vitamin B12 is rare because the vitamin is found in meats, milk, eggs, and cheese. The body is also able to store this vitamin a deficiency, for any reason, will not occur for 5 to 6 years. 

Iron-deficiency anaemia results from a discrepancy between iron availability and the amount required for production of red blood cells. The causes of acquired iron deficiency in so-called underdeveloped and developed countries must be differentiated. In underdeveloped countries, the main causes of iron deficiency are (a) the poor availability of iron in the diet due to low haem and high fibre and phytate content (D Souza et ah, 1987), and (b) chronic blood loss due to hookworm, schistosomiasis and malaria (Stoltzfus et ah, 1997 Olsen et ah, 1998 Dreyfuss et ah, 2000). Inflammation and vitamin A deficiency often interfere with the above causes of iron deficiency, causing a mixed type of anaemia. In underdeveloped countries diet improvement, iron fortification of natural foods and eradication of parasites will have a much higher impact than will refinement of diagnostic procedures and therapy of iron-deficiency anaemia. 

On the basis of a few reports, it is assumed that a "local vitamin A deficiency exists in meta- and dysplastic areas. Measurements of vitamin A concentrations in metaplastic areas of the respiratory epithelium and the cervix epithelium actually proved that vitamin A in comparison to the surrounding tissues was not found (Biesalski, 1996). Clearly one cannot say what is cause and effect. Studies carried out by Edes et al. (1991) confirm an induction of a vitamin A deficit. These studies showed that a depletion of vitamin A ester stores is caused by toxins, present in cigarette smoke (predominantly polyhalogenated compounds), in different tissues. 

Such changes (decrease of ciliated cells with simultaneous increase of the secretion) are noted for smokers (Gouveia et al., 1982 Mathe et al., 1983) and cause a reduction of the mucociliary clearance. This reduction of the mucociliary clearance, associated with an increased adsorption of the respiratory syncytial virus (RSV) (Donelly, 1996), could also explain the extraordinarily high morbidity and mortality for respiratory infections of children with vitamin A deficiency in developing coimtries (Sommer, 1993). 

Vitamin A deficiency is worldwide one of the most prevalent nutrition-dependent deficiency diseases. It leads to changes of the respiratory epithelium, which result in repeated infections of the respiratory tract, the main cause of death in vitamin A-deficient children. The difficulty in supplying the respiratory epithelium with vitamin A is that the affected children frequently suffer as well from infections of the gastrointestinal tract with subsequent reduction of the absorption of fat-soluble vitamins. Nutritargeting can in these cases avoid the problems of malabsorption and ensure the micronutrient supply. 

Oxidation of fatty acids with an odd number of carbons proceeds two carbons at a time (pro ducing acetyl CoA) until the last three carbons (propionyl CoA). This compound is con verted to methylmalonyl CoA (a reaction requiring biotin), which is then converted to succinyl CoA by methylmalonyl CoA mutase (requiring vitamin B )- A genetic error in the mutase or vitamin B12 deficiency causes methylmalonic acidemia and aciduria. 

In large areas of the world, the soils contain very little selenium in forms that can be taken up by plants. Crops produced in these areas are, therefore, very low in selenium. A selenium (deficiency in livestock is a serious problem. A deficiency causes a form of muscular dystrophy in younger animals and poor reproductive qualities in the adult animals. For prevention, sodium selenate or sodium selenite, sometimes augmented with vitamin E. is added in proper proportions to feedstuffs Some areas, including the Plains and Rocky Mountain states in the United States have soils that are rich in available selenium. Tn regions like these, selenium toxicity is a problem. The situation is particularly senous in Arizona, California, Montana, Nevada, New Mexico, and South Dakota. 

Wang, Z. et al., Ultraviolet irradiation of human skin causes functional vitamin A deficiency, preventable by all-trans retinoic acid pre-treatment, Nature Med., 5, 418, 1999. 

Vitamin A absorbs UV light between 300 and 350 nm. After acute exposure to UVA or UVB a dose-dependent decrease of vitamin A was shown in mouse59 and humans.84 UV irradiation markedly reduced mRNA and protein of the nuclear retinoid receptors RARy and RXRa in humans and led to a near loss of retinoic acid induction of the RAR/RXR target genes and the cellular retinoic acid binding protein II thus effectively causing additionally a functional vitamin A deficiency.85... 

How does a vitamin B12 deficiency cause a decrease in the hematocrit and hemoglobin concentration ... 

Cystic fibrosis patients are usually advised to take more than the recommended daily amounts of these vitamins in order to prevent deficiency. A common problem associated with poor absorption of fat-soluble vitamins is deficiency of vitamin K. Vitamin K is required by the liver to produce many blood coagulation factors. Part of the problem for cystic fibrosis patients is their chronic antibiotic therapy, which decreases the bacterial population of the colon colonic bacteria synthesize vitamin K. Vitamin K deficiency leads to prolonged blood-clotting time. Vitamin D deficiency could cause rickets in a child or osteomalacia in adults. Vitamin A deficiency leads to night blindness, skin and other ocular defects. 

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