The Impact of Micronutrient Deficiencies on Immune Function

Micronutrients are required in small quantities, but their effects on immunity are large because immune defense depends on cell division, epithelial integrity, redox control, cytokine signaling, antibody formation, and tissue repair. This paper critically examines how deficiencies of key vitamins and minerals impair immune function and increase vulnerability to infection, delayed recovery, inflammation, and poor vaccine response. The review focuses on vitamins A, C, D, E, B6, B12, and folate, and the minerals iron, zinc, selenium, iodine, and copper. It explains the immune system as a layered defense consisting of physical barriers, innate immune responses, adaptive lymphocyte responses, and immunological memory. Deficiencies affect each layer differently: vitamin A compromises mucosal integrity, vitamin D regulates antimicrobial peptides and inflammatory balance, vitamin C supports epithelial and phagocyte function, zinc affects thymic activity and lymphocyte development, iron has a dual role in host immunity and pathogen growth, and selenium protects against oxidative damage. The paper also discusses the double risk of deficiency and excess, emphasizing that supplementation should correct inadequacy rather than promote indiscriminate high-dose use. Global evidence indicates that inadequate micronutrient intakes remain widespread, with serious implications for children, adolescents, women, older adults, displaced populations, and people with chronic disease. Interventions include dietary diversification, fortification, targeted supplementation, infection control, and monitoring of vulnerable groups. The paper concludes that micronutrient adequacy is a foundational condition for immune competence, but it works best as part of an integrated public-health approach that includes food security, vaccination, sanitation, clinical care, and equity-oriented nutrition policy.