الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Vitamin A is a fat- soluble vitamin that essential for life of all vertebrate. It is very important as it has many functions including; vision, regulation of immune function , intercellular communication, growth, development, reproduction and regulation of nuclear transcription via nuclear receptor coupling related to cellular growth and differentiation (Mody, 2017). The major forms of vitamin A are: The preformed vitamin (retinoid) and provitamin A (carotene), Figure 1. Retinoids are retinol, retinal and retinoic acid, where retinoic acid is the active metabolite of vitamin A (Rhee & Plutzky, 2012). Retinoids typically have four isoprenoid units joined head to tail, and contain five conjugated carbon- carbon double bonds. Vitamin A can be obtained from foods of animal origin, such as organ meats, fish oil, dairy products, in the preformed vitamin (retinoid) form, and from plant -origin foods, such as orange, yellow, and green vegetables and fruits, as provitamin A (carotene). The metabolic process that transform carotene into retinol different from one to another so the bio-aviability of carotene in food is different (Tang et al., 2005; Solomons, 2012).