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

The vitamin that is primarily produced in the skin when exposed to sunlight is Vitamin D. When the skin is exposed to ultraviolet (UV) rays from the sun, a chemical reaction occurs that leads to the conversion of 7-dehydrocholesterol, a compound found in the skin, into previtamin D3. This then undergoes a thermal isomerization to become vitamin D3, which is later converted by the liver and kidneys into the active form of vitamin D, known as calcitriol.

Vitamin D plays a crucial role in calcium absorption and bone health, as well as having important functions in the immune system. The body relies on UV exposure as a significant source of this essential nutrient, making it unique among the vitamins listed, which do not have a similar production mechanism in the skin.