Which vitamin is primarily produced when skin is exposed to sunlight?

When skin is exposed to sunlight, specifically to ultraviolet B (UVB) rays, it triggers the production of vitamin D. This process begins when the skin absorbs UVB radiation, which converts a cholesterol derivative in the skin (7-dehydrocholesterol) into pre-vitamin D3, which then further transforms into active vitamin D3 (calcitriol) through heat and other processes in the body.

Vitamin D is essential for various bodily functions, including the regulation of calcium and phosphorus, which are vital for maintaining healthy bones and teeth. It also plays a crucial role in immune system function.

The other vitamins listed do not have the same mechanism of production through sun exposure. Vitamin A is primarily obtained through dietary sources as retinol or beta-carotene; vitamin B12 is also obtained through animal-derived foods and is not synthesized by the body through sunlight, and vitamin C, while important for collagen production and immune function, is obtained mainly from fruits and vegetables, independent of sunlight exposure.