The Role of Diet and Physical Exercise in Immunity Boosting: Health and Wellbeing across the Lifespan

Malnutrition, particularly diet-related deficiencies, remains the most prevalent cause of immunodeficiency worldwide and plays a pivotal role in shaping immune responses. Protein–energy malnutrition has been strongly associated with impaired cell-mediated immunity, reduced phagocytic activity, altered complement function, decreased concentrations of secretory immunoglobulins and antibodies, and diminished cytokine production. Even mild deficiencies of single nutrients can disrupt immune competence. Among micronutrients, zinc, selenium, iron, copper, and vitamins A, C, E, B6, along with folic acid, exert essential regulatory effects on immune mechanisms. Conversely, overnutrition and obesity are also linked to immune suppression and increased susceptibility to infections. Low-birth-weight infants often experience prolonged deficits in cell-mediated immunity, which may be partially corrected by supplementation with zinc. The COVID-19 pandemic has highlighted the critical link between immune status and viral susceptibility, as weakened immunity is a well-established risk factor for influenza-like illnesses and coronavirus infections. In this context, functional foods and nutraceuticals have gained attention for their ability to modulate immune responses and provide antiviral protection. Compounds such as polyphenols, terpenes, flavonoids, sterols, unsaturated fatty acids, and essential vitamins and amino acids contribute antioxidant and immunomodulatory benefits. Functional diets enriched with fruits, vegetables, fermented foods, probiotics, olive oil, fish, nuts, seeds, herbs, roots, mushrooms, and bioactive peptides are considered potent antiviral resources. In parallel, physical exercise plays a complementary role in enhancing immunity. Acute, short-term, and long-term adaptations to moderate exercise strengthen both innate and adaptive immune systems in a dose-dependent manner. Regular moderate physical activity, combined with balanced nutritional practices, not only reduces vulnerability to viral infections, including COVID-19, but also improves overall wellbeing and sleep quality, particularly during periods of confinement. Integrating functional nutrition with lifestyle interventions provides a promising public health approach for boosting immunity and reducing the burden of both communicable and non-communicable diseases.