Which vitamin can be synthesized by the body with adequate sunlight exposure?

Vitamin D is unique among vitamins because it can be synthesized by the body when the skin is exposed to adequate sunlight, specifically ultraviolet B (UVB) radiation. The process begins when UVB rays convert a cholesterol derivative in the skin into previtamin D3, which is then converted to active vitamin D (calcitriol) through further processes in the liver and kidneys.

This synthesis is significant because vitamin D plays a crucial role in calcium absorption, bone health, immune function, and overall metabolic processes. Inadequate sun exposure can lead to deficiencies, highlighting the importance of sunlight for maintaining sufficient levels of this vitamin in the body.

The other options do not follow this pathway: Vitamin C, B12, and A must be obtained through diet rather than being synthesized from sunlight, which distinguishes vitamin D's unique status as a vitamin that the body can produce given proper environmental conditions.