Vitamin A is fat-soluble compounds of retinoid derivate, consisting of retinol, retinal, and retinyl esters. Vitamin A also affects cell growth and differentiation, playing a critical role in the normal formation and function of the heart, lungs, kidneys, and other organs. According to the role of vitamin A in enhancing immune function, it is known as an anti-inflammatory agent. Also, vitamin A supplementation by reducing morbidity and mortality in different infectious diseases, such as measles, diarrheal disease, measles-related pneumonia, human immunodeficiency virus infection, and malaria considered as a crucial factor against infection. So vitamin A deficiency can be life-threatening, because of impairing the response to infection and significant risk of development of severe respiratory infections in infants and young children. In this paper, we have discussed the effects of vitamin A in modulating immune responses in viral infections and the direct effects of this vitamin on viral replication by comparing its role during different types of viral infections.
