Deficiencies that most commonly impair immune response include vitamin A, vitamin D, vitamin C, zinc, iron, and selenium, each supported by clinical and mechanistic research linking nutrient status to infection risk, inflammation, and vaccine responsiveness. These nutrients act at different immune checkpoints: barrier integrity, innate cell function, adaptive responses, and redox balance.
Evidence and key researchers
Vitamin D influences innate antimicrobial peptides and adaptive immunity; a major meta-analysis led by Adrian Martineau, Queen Mary University of London, found supplementation reduced risk of acute respiratory infections in certain groups. Zinc is essential for T-cell development and antiviral defenses; pioneering work by Ananda S. Prasad, Wayne State University, documents how zinc deficiency impairs cellular immunity and increases morbidity. Vitamin A is crucial for mucosal integrity and antibody responses; Keith P. West Jr., Johns Hopkins Bloomberg School of Public Health, has published on vitamin A deficiency as a contributor to infection-related child mortality. Vitamin C supports neutrophil function and antioxidant defenses; Anitra C. Carr, University of Otago, has summarized vitamin C’s role in immune cell function and recovery from infections. Selenium affects viral mutation and immune regulation; Margaret P. Rayman, University of Surrey, has reviewed how low selenium status is associated with poorer outcomes in viral illnesses. Iron deficiency, often discussed in WHO-led nutrition policy by Francesco Branca, World Health Organization, reduces proliferation of immune cells and can blunt vaccine responses while also complicating infection risk due to anemia.Causes, relevance, and consequences
Deficiencies arise from inadequate dietary intake, poor absorption, inflammation-driven sequestration, restrictive diets, poverty, aging, and limited sunlight for vitamin D. Soil composition and geography affect selenium levels in local food systems, creating territorial patterns of deficiency, while cultural diets and food systems mediate vitamin A and iron availability. Consequences include increased susceptibility to respiratory and enteric infections, prolonged illness, higher complication rates, and reduced efficacy of vaccinations. In clinical practice, correcting deficiencies can reduce infection burden, though the benefit depends on baseline status, dose, and timing.Public health measures—fortification, targeted supplementation, improved diet diversity, and addressing underlying poverty and sanitation—are evidence-based strategies used globally to mitigate these deficiencies. Clinical assessment and laboratory testing guided by clinicians and nutrition experts remain essential, especially for vulnerable populations such as children, pregnant people, older adults, and those with chronic disease.