Essential vitamins for maintaining a healthy immune system include Vitamin C, Vitamin D, Vitamin A, and the B vitamins. Vitamin C is crucial for the growth and repair of tissues and helps produce antibodies, while Vitamin D plays a role in the activation of immune cells. Vitamin A supports immune function and helps maintain the health of mucosal barriers. The B vitamins are important for energy production and overall metabolic function. Including a variety of fruits, vegetables, and whole grains supports adequate intake of these vitamins and promotes a robust immune response.