Malnutrition and Immune Function

Malnutrition and immune function describes how deficits in energy, protein, and specific micronutrients impair the body's defences against infection. Protein-energy malnutrition and several micronutrient deficiencies compromise barrier integrity, innate immunity, and adaptive (notably cell-mediated) immunity, producing a state sometimes called nutritionally acquired immunodeficiency. Because impaired immunity in turn raises the burden of infection, malnutrition sits at the heart of the nutrition-infection synergism.

Definition

Malnutrition and immune function refers to the impairment of innate and adaptive immune defences that results from protein-energy malnutrition and micronutrient deficiency, increasing host susceptibility to and severity of infection.

Scope

The topic covers the principal ways in which undernutrition weakens host defence: effects on physical and mucosal barriers, on innate immune cells, and on the adaptive immune system, together with the roles of key micronutrients. It situates these mechanisms within the broader nutrition-infection cycle and its population consequences. The treatment is mechanistic and reference-oriented, not a clinical protocol.

Key concepts

• Protein-energy malnutrition
• Nutritionally acquired immunodeficiency
• Cell-mediated immunity impairment
• Mucosal and barrier defence
• Micronutrients (e.g. vitamin A, zinc, iron) and immunity
• Thymic and lymphoid atrophy
• Nutrition-infection synergism

Mechanisms

Undernutrition impairs immunity at several levels. Protein-energy malnutrition is associated with atrophy of the thymus and other lymphoid tissue and with marked depression of cell-mediated immunity, while also weakening epithelial and mucosal barriers that normally exclude pathogens. Specific micronutrients modulate immune function: deficiencies of nutrients such as vitamin A, zinc, and iron, among others, alter the number and activity of immune cells and the integrity of host defences. Cunningham-Rundles and colleagues review the cellular and molecular pathways through which nutrients modulate immune responses, and Scrimshaw and colleagues frame the net effect as a synergism in which weakened immunity and infection reinforce one another.

Clinical relevance

Recognising that malnutrition compromises immune defence helps explain why undernourished populations experience more frequent and more severe infection. The content describes mechanisms and population patterns and is reference-educational; it does not provide diagnostic thresholds, supplementation regimens, or individualised treatment advice.

Epidemiology

Because impaired immunity translates into excess infection, undernutrition is a leading underlying contributor to infectious-disease morbidity and mortality, especially among young children in low- and middle-income settings. The Lancet undernutrition series estimated that a substantial fraction of child deaths are attributable to the underlying effect of undernutrition, much of it mediated through increased vulnerability to infection.

History

The link between malnutrition and weakened defence against infection was formalised in mid-twentieth-century work, with Scrimshaw and colleagues integrating clinical and field evidence into the concept of a nutrition-infection-immunity synergism. Later research refined the picture by characterising the immunological roles of individual micronutrients and the cellular mechanisms of nutrient modulation, while global epidemiological syntheses quantified the resulting disease burden.

Key figures

• Nevin Scrimshaw
• Susanna Cunningham-Rundles
• Peter Katona
• Robert E. Black

Seminal works

• scrimshaw-1997
• cunningham-rundles-2005
• katona-2008

Frequently asked questions

Why does malnutrition increase the risk of infection?

Deficits in energy, protein, and key micronutrients weaken physical and mucosal barriers and depress innate and cell-mediated immunity, so undernourished hosts are less able to resist pathogens and tend to experience more frequent and more severe infections.

Which part of the immune system is most affected by undernutrition?

Cell-mediated immunity is classically the most affected, with protein-energy malnutrition associated with lymphoid atrophy and reduced T-cell function, although barrier defences and several micronutrient-dependent pathways are also impaired.