The immune system as a guardian of health: micronutrient support and lifelong protection.

The immune system constitutes a physiological network that preserves organismal stability through continuous interactions with tissues and regulatory systems. Immune activity is an integral component of normal tissue physiology, contributing to host defense, structural integrity, metabolic balance, and functional homeostasis. The immune system integrates molecular recognition, effector mechanisms, and inflammation resolution to control infections, limit tissue damage, and reduce the progression of chronic and degenerative diseases. These combined defensive and physiological functions underpin the concept of the immune system as a "guardian of health." Immune competence varies across the life course, following a dynamic trajectory shaped by development, maturation, stabilization, and age-related decline (immunosenescence). Early life, adolescence, pregnancy, menopause, and aging are characterized by increased immune plasticity and shifting functional demands. In later life, immunosenescence and chronic low-grade inflammation (inflammaging) increase immune vulnerability, to the extent that immune resilience determines interindividual variability with aging and subsequent health outcomes. Micronutrients are central determinants of immune resilience, as they support immune cell proliferation and function, redox balance, epithelial barrier integrity, and inflammation control. Vitamins A, C, D, E, and the B-group, together with trace elements such as zinc, selenium, iron, and copper, act within interconnected metabolic and signaling networks that sustain innate and adaptive immune responses. Despite their essential role, subclinical micronutrient insufficiencies remain common, including in high-income countries, and are associated with reduced immunocompetence and increased susceptibility to infection and inflammation. Overall, this evidence highlights that life-course-based immunonutrition could be a strong strategy to preserve health-span and promote long-term physiological resilience.