Vitamin C is an essential micronutrient with multifaceted roles in the immune system. It acts as a potent antioxidant, supports epithelial barrier function, and enhances the activity of phagocytic cells such as neutrophils. Vitamin C is crucial for the differentiation and proliferation of B- and T-cells, and it plays a key role in wound healing and tissue repair. Deficiency in vitamin C can lead to impaired immunity and increased susceptibility to infections, while infections can significantly impact vitamin C levels due to enhanced inflammation and metabolic demands. Supplementation with vitamin C can both prevent and treat respiratory and systemic infections, with prophylactic doses ranging from 100 to 200 mg/day and therapeutic doses in grams. The review highlights the importance of maintaining adequate vitamin C status to support immune function and resistance to infections, especially in vulnerable populations such as the elderly and those exposed to risk factors for vitamin C insufficiency.Vitamin C is an essential micronutrient with multifaceted roles in the immune system. It acts as a potent antioxidant, supports epithelial barrier function, and enhances the activity of phagocytic cells such as neutrophils. Vitamin C is crucial for the differentiation and proliferation of B- and T-cells, and it plays a key role in wound healing and tissue repair. Deficiency in vitamin C can lead to impaired immunity and increased susceptibility to infections, while infections can significantly impact vitamin C levels due to enhanced inflammation and metabolic demands. Supplementation with vitamin C can both prevent and treat respiratory and systemic infections, with prophylactic doses ranging from 100 to 200 mg/day and therapeutic doses in grams. The review highlights the importance of maintaining adequate vitamin C status to support immune function and resistance to infections, especially in vulnerable populations such as the elderly and those exposed to risk factors for vitamin C insufficiency.