Which vitamin is primarily synthesized in the skin?

Vitamin D is primarily synthesized in the skin through a process that begins when the skin is exposed to ultraviolet B (UVB) radiation from sunlight. When UVB rays strike the skin, they convert a cholesterol derivative (7-dehydrocholesterol) present in the skin into previtamin D3. This previtamin is then thermally converted into vitamin D3 (cholecalciferol) in the skin.

Once synthesized, vitamin D3 is transported to the liver and kidneys, where it is further converted into its active form, calcitriol. Vitamin D plays a crucial role in calcium absorption, bone health, and various other physiological processes. This ability to produce vitamin D in the skin highlights the crucial relationship between sunlight exposure and our skin, showcasing the integumentary system's role in synthesizing essential nutrients for our body.

In contrast, vitamins A, B12, and C do not undergo synthesis in the skin and must be obtained from dietary sources or supplements.