ABSTRACT
Vitamin A is essential for regulating a number of key biological processes in the body and contributes to the normal functioning of the visual system, growth and development, maintenance of epithelial cellular integrity, immune function, and reproduction [1]. Vitamin A is known to be involved in maintaining immuno-competence by helping to maintain the lymphocyte pool and playing a role in T-cell-mediated responses [2, 3]. Neither humans nor animals can synthesize or survive without vitamin A. It is therefore vital that the micronutrient vitamin A is provided in the diet in sufficient amounts to meet all the physiological needs. Key functions of vitamin A are summarized in Table 16.1.
