Which one of the following vitamins is synthesized in our own skin?

Vitamin D is uniquely known as the "sunshine vitamin" because it is synthesized in the human skin upon exposure to ultraviolet B (UVB) radiation [1]. The process begins in the epidermal layer of the skin, where a cholesterol derivative called 7-dehydrocholesterol absorbs UVB rays and is converted into previtamin D3 [2]. This precursor then undergoes thermal isomerization to form vitamin D3 (cholecalciferol) [4]. Once synthesized, it enters the bloodstream and is sequentially metabolized in the liver and kidneys to its biologically active form, calcitriol, which is essential for calcium and phosphate absorption [1]. In contrast, most other vitamins, such as Vitamin B12, cannot be produced by the human body and must be obtained through dietary sources [1]. While the skin is a target for other vitamins like A and C, they are not synthesized there.

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC3897598/
2. [2] https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/previtamin-d3
3. [4] https://www.ncbi.nlm.nih.gov/books/NBK278935/