Which vitamin is synthesized by the body when exposed to sunlight?

The body synthesizes vitamin D when the skin is exposed to ultraviolet (UV) rays from sunlight. This process begins when UV radiation converts a cholesterol derivative in the skin into vitamin D3 (cholecalciferol). Once formed, vitamin D3 is then converted in the liver and kidneys into its active form, calcitriol, which is crucial for maintaining calcium homeostasis and promoting bone health.

Vitamin D is unique among vitamins because it can be produced by the body in sufficient amounts given adequate sunlight exposure, making it not just a dietary vitamin but one that can also be synthesized. This characteristic highlights the importance of sunlight in vitamin D metabolism and its role in overall health.