Vitamin A also supports adaptive immunity. Indeed, retinoids represents physiological modulators of normal B cell growth and differentiation, thus vitamin A deficiency negatively affects B cell function [18]. Furthermore, animal studies have shown impairment in the antibody response due to vitamin A deficiency [19]. The production of antibodies may be enhanced by the influence of vitamin A on T helper 2 cells development [22] and antigen-presenting cells [15,23]. In addition, retinoids induce the differentiation of Tregs and maintain both the stability of Tregs and their immunoregulatory function [24]. Indeed, retinoids play fundamental roles in cell-mediated immunity, representing an important cofactor in T cell activation [25] and influencing the expression of membrane receptors that mediate T-cell signalling [17]. Vitamin A supplementation trials conducted in paediatric populations have shown the potential effect to increase T-cell, particularly of the CD4 subpopulation [15,26].