The vitamin primarily associated with boosting the immune system is vitamin C. This powerful antioxidant plays a role in supporting various cellular functions of both the innate and adaptive immune systems. It helps stimulate the production of white blood cells, which are crucial for fighting infections. Rich sources of vitamin C include citrus fruits, berries, peppers, and broccoli. Regular consumption of these vitamin C-rich foods can enhance immune response and may reduce the duration and severity of illnesses.