Iron and immunity

Review of animal and human studies concerning the impact of iron deficiency on immune function in vivo indicates that in many instances there is no firm consensus of opinion as to the relationship between iron status and immunity. One major problem with almost all human studies is that other micro- and macronutrient deficiencies are inadequately controlled for and thus it is often unclear as to whether reported abnormalities of immune function can be attributed specifically to iron deficiency. Even when abnormalities of immune function have been detected it is often uncertain as to the biological and clinical relevance that these may have for the host. Within these restraints the available studies suggest that iron deficiency may at least contribute to impaired T lymphocyte function as judged by DTH responses in skin and impaired mitogen-induced proliferation. As in protein energy malnutrition, humoral immunity is largely spared in humans, the balance of evidence suggesting that immunoglobulin production and function is normal, as are serum concentrations of complement. The only other abnormality of non-specific immunity which has been reported consistently to be abnormal is that of reduced bactericidal activity of polymorphonuclear leucocytes. The clinical relevance of these abnormalities remains to be established. There is, however, no evidence to suggest that individuals with iron deficiency suffer the devastating infective complications of the well defined immunodeficiency syndromes either congenital or acquired. It seems likely therefore that despite the fundamental importance of iron in maintaining the integrity of immune function, humans can tolerate the extremes of deficiency and excess and survive in a relatively healthy state.