ABSTRACT
Epidemiological studies have indicated that even relatively mild vitamin A deficiency may be associated with increased infections and morbidity, particularly in infants and children, and that vitamin A deficiency is associated with a decreased immune response. In vitro studies allow rapid delineation of the direct effects of micronutrients on macrophages or lymphocytes. However, high intakes of vitamin A and their effects should receive more attention and study. Vitamin A in high concentration may directly affect lymphocyte growth or maturation. The exact mechanism responsible for increased liver toxicity of certain xenobiotics in the presence of excess vitamin A is unknown. Conceivably, it may involve both potentiation of the primary effect of the toxin on liver parenchymal cells as well as some consequence of stimulation of liver macrophages acting either independently or in concert with a more generalized effect of vitamin A on the immune system.
