Micronutrients: Immunological and Infection Effects on Nutritional Status and Impact on Health in Developing Countries

Abstract

• Deficiencies of micronutrients (vitamins, minerals and trace elements) are common—up to a third of people in low-income countries are affected. • Women and children, especially those living in poverty, are those most at risk because of increased metabolic demands of growth, pregnancy and lactation and repeated infections. • A vicious cycle of undernutrition leads to reduced immunity that increases disease risk and then the disease itself causes further undernutrition and so on. • Immune systems are impacted by micronutrient deficiencies: – vitaminAdeficiency impairs innate, cell-mediated and humoral antibody responses but probably not viral infec- tion – zinc deficiency affects both innate and cell-mediated immunity but effects of supplementation on antibody production in humans are less clear than in animals – iron deficiency and overload impair both innate and cell-mediated immunity,with no effect on humoral antibody production – vitamin C deficiency in humans impairs leukocyte functions and decreases overall NK cell activity and lym- phocyte proliferation – vitamins B6, B12, folate and E deficiencies impair Th1 cytokine-mediated immune response through insuffi- cient production of pro-inflammatory cytokines, shifting to an anti-inflammatory Th2 cell-mediated immune response, thus increasing the risk of extracellular infections – supplementation with micronutrients generally reverses these impaired immune responses • Micronutrient deficiencies can also be addressed by dietary improvement (if available and accessible), and by forti- fication. It is important to also address other interventions such as immunization, water and sanitation, breastfeeding and the reduction of social inequities.