The micronutrient crucial for maintaining a healthy immune system is vitamin C. It plays an important role in supporting various cellular functions of both the innate and adaptive immune system. Vitamin C is a potent antioxidant that helps protect against cellular damage and is involved in the production of white blood cells, which are essential for fighting infections. Fruits and vegetables, particularly citrus fruits, strawberries, bell peppers, and broccoli, are rich in vitamin C.