Vitamin A in Health and Disease

Vitamin A refers to a group of related compounds with all-trans retinol biological activity and includes retinol, retinal, retinoic acid as well as the retinyl esters. Dietary source of vitamin A ranges from animal-based or plant-based foods, fortified food products and supplements. The vital biological roles of vitamin A compounds include normal cell growth, cell differentiation, vision and immunology. Vitamin A status is monitored to prevent occurrence of both subclinical deficiency and toxicity. Vitamin deficiency or excess is determined through the measure of vitamin A status. Prolonged vitamin A intake at high doses is shown to be toxic, which leads to various health symptoms. Xerophthalmia, a dry eye condition is the most severe clinical effects known to be caused by vitamin A deficiency. The resulting deleterious effects on human health led to efforts of supplementation, food fortification and dietary diversification in combating vitamin A deficiency. In brief, this chapter covers on vitamin A, with focus on its general information, dietary recommendations, biological roles, vitamin A status assessment, deficiency or excess effects to human health as well as the prevention measures.