Toxicity , 24-6 xerophthalmia

Avitaminosis A results in the loss of night vision nyctalopia). Furthermore, the removal of vitamin A from the diet causes the cornea of the eye to dry out xerophthalmia). However, excessive intake of vitamin A can result in severe and even fatal toxicity. 

Impotence Night blindness Retardation of growth Xerophthalmia Increased visuel threshold Dryness of cornea Yes FAT-SOLUBLE p-Carotene not acutely toxic, but supplementation is hot recommended Excess vitamin A can increase incidence of fractures... 

Vitamin A (retinol, retinal, retinoic acid—the three active forms of vitamin A, and p-carotene) function in the maintenance of reproduction, vision, promotion of growth, differen tiation and maintenance of epithelial tissues, and gene expression. A deficiency of vitamin A results in impotence, night blindness, retardation of growth, and xerophthalmia. Large amounts of vitamin A are toxic and can result in an increased incidence of frac tures. 

A Dermatitis, night blindness, keratomalacia, xerophthalmia Serum vitamin A Teratogenic effects, liver toxicity with excessive intake alcohol intake, liver disease, hyperlipidemia, and severe protein malnutrition increase susceptibility to adverse effects of high intake , 6-carotene supplements recommended only for those at risk of deficiency (fat malabsorption)... 

Health is unquestionably compromised by abnormal vitamin A nutriture at the extremes of too little (xerophthalmia/keratomalacia/irreversible blindness) or too much (toxicity). However, the health and social consequences of subclinical or marginal nutritional states are yet to be fully delineated. This section considers the criteria used to define a public health problem, the geographic distribution of hypovitaminosis A at varied levels of severity, and programs initiated for its control. Consideration is then given to hypervitaminosis A. 

Vitamin A is transported from the gut to the liver in chylomicrons, and from the Hver to the tissues bound to a specific retinal-binding protein or pre-albumin. Deficiency of vitamin A is usually associated with poor protein diets. It is not necessarily reversible by administration of vitamin A alone since the synthesis of retinolbinding protein is affected by the deficiency and therefore so is vitamin A absorption. Deficiency may cause night blindness, xerophthalmia and keratomalacia. Vitamin A toxicity is unUkely with a normal diet but can cause dermatitis, hair loss, and hepatic dysfunction. In pregnancy it can cause teratogenicity if taken in... 

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