In the case of human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS), studies have shown that the action of micronutrients can be targeted at at least four different levels of nutrient-host interactions, which include: (i) suppression of virus replication or activation in infected cells; (ii) modulation or enhancement of immune cell production or function to fight opportunistic infection; (iii) reduction in rate of disease progression; and (iv) lowering of AIDS-defining or associated physical symptoms. In the case of tuberculosis (TB), micronutrients have been found to be capable of reducing pathological symptoms and controlling the tubercle bacillus. With viral influenza, though evidence points to a role for micronutrients in improving immunity, blocking viral infectivity/multiplication and suppressing the secretion of cellular proteases required for virus spread. Here, we review the salient features of the scientific evidence for micronutrients and their specific combinations in modulating immunodeficiency and infectious diseases.