Immune Function and Micronutrient Requirements Change over the Life Course

Abstract

As humans age, the risk and severity of infections vary in line with immune competence according to how the immune system develops, matures, and declines. Several factors influence the immune system and its competence, including nutrition. A bidirectional relationship among nutrition, infection and immunity exists: changes in one component affect the others. For example, distinct immune features present during each life stage may affect the type, prevalence, and severity of infections, while poor nutrition can compromise immune function and increase infection risk. Various micronutrients are essential for immunocompetence, particularly vitamins A, C, D, E, B2, B6, and B12, folic acid, iron, selenium, and zinc. Micronutrient deficiencies are a recognized global public health issue, and poor nutritional status predisposes to certain infections. Immune function may be improved by restoring deficient micronutrients to recommended levels, thereby increasing resistance to infection and supporting faster recovery when infected. Diet alone may be insufficient and tailored micronutrient supplementation based on specific age-related needs necessary. This review looks at immune considerations specific to each life stage, the consequent risk of infection, micronutrient requirements and deficiencies exhibited over the life course, and the available evidence regarding the effects of micronutrient supplementation on immune function and infection.

Keywords: adults; age-related immunity; deficiency; elderly; immunosenescence; infants; infection; micronutrients; older people.

Figure 1

Simple overview of the immune system. The three layers of the immune system (physical and biochemical barriers; cells such as monocytes, granulocytes, lymphocytes, and B and T cells; and antibodies or immunoglobulins) work together to protect the body against pathogens, utilizing the innate and adaptive defense mechanisms. All three layers are involved in the innate and immune systems. * The innate immune system comprises anatomical and biochemical barriers and an unspecific cellular response mediated mainly by monocytes, neutrophils, natural killer cells and dendritic cells; these work together to fight off pathogens before they can start an active infection. ** The adaptive immune system involves an antigen-specific response mediated by T and B lymphocytes that is activated by exposure to pathogens; this works with the innate immune system to reduce the severity of infection. ^a The complement system can work with both the innate and adaptive immune systems; ^b i.e., immunity from serum antibodies produced by plasma cells; ^c i.e., an immune response that does not involve antibodies, but responds to any cells that display aberrant major histocompatibility complex (MHC) markers, such as cells invaded by pathogens.

Figure 2

Life-style factors affecting immune function during adulthood. The risk of infection is also influenced by gender, early programming, vaccination history, pathogen exposure, specific health conditions, and diseases.

Figure 3

Differences in immunity and nutrition over a lifetime. Ca, calcium; Cu, copper; Fe, iron; I, iodine; Ig, immunoglobulin; Mg, magnesium; NK, natural killer; RTI, respiratory tract infections; Se, selenium; Th, T helper cell; Zn, zinc.