Which micronutrient is crucial for immune function?

All of the mentioned vitamins—A, D, and C—play vital roles in supporting immune function, making "All of the above" the correct answer.

Vitamin A is essential for maintaining the structural and functional integrity of mucosal cells, which serve as a barrier to pathogens. It is also involved in the development and differentiation of immune cells, particularly lymphocytes.

Vitamin D is important for immune regulation. It enhances the pathogen-fighting effects of monocytes and macrophages—white blood cells that are crucial for the immune response. Adequate levels of Vitamin D can help lower the risk of infections.

Vitamin C is a powerful antioxidant that contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune system. It has been shown to encourage the production of white blood cells, which protect the body against infection.

Each of these vitamins plays a unique and complementary role in enhancing and regulating immune responses, thus underscoring the importance of a balanced intake of all three for optimal immune health.