ABSTRACT
Vitamin A, an essential lipid-soluble nutrient, was first discovered in eggs, milk, butter, and fish liver oils. Plants contain vitamin A in the form of its provitamin, β-carotene. In recent years the term "retinoids" has been designated as a general term that includes both natural forms of vitamin A and its synthetic analogs. Vitamin A is necessary for the support of growth, health, and life of all vertebrates and for the prevention of night blindness. Vitamin A is necessary for the maintenance of differentiated epithelia, for reproduction, and for glycoprotein production. The trans-vitamin A alcohol or trans-retinol is the parent substance and its naturally occurring oxidation products are trans-retinal (vitamin A aldehyde) and trans-retinoic acid (vitamin A acid). The retinoid molecule can be chemically modified in many ways into unlimited numbers of compounds. The nutritional role of vitamin A has been extensively reviewed.
