Nutritional regulation of immunity and risk of illness.

Nutrition is a critical determinant of immunocompetence and risk of illness. Young children with protein-energy malnutrition exhibit increased mortality and morbidity, largely due to infectious disease. Recent work has demonstrated that, undernourished individuals have impaired immune responses. The most consistent abnormalities are seen in cell-mediated immunity, complement system, phagocytes, mucosal secretory antibody response, and antibody affinity. These changes, together with other handicapping factors observed in underprivileged societies, lead to more infections, which in turn produce physiological changes that worsen nutritional status. It is now established that deficiencies of single nutrients also impair immune responses. The best studied are zinc, iron vitamin B6, vitamin A, copper and selenium. If malnutrition occurs during fetal life, as epitomized by small-for-gestational age infants, the effects on cell-mediated immunity are very significant and long lasting. These interactions on nutrition and immunity have several practical applications.