Which skin function helps synthesize vitamin D from sunlight?

• A. The skin converts retinol to retinal to form active vitamin D.
• B. The skin converts 7-dehydrocholesterol to vitamin D3 (cholecalciferol) when exposed to UVB light.
• C. The skin secretes intrinsic factor to enable vitamin D absorption in the small intestine.
• D. The skin produces bile acids that emulsify dietary fat to absorb vitamin D.

Answer: (B)

Verified step by step guidance

1. Understand that vitamin D synthesis in the body primarily occurs in the skin through a photochemical reaction triggered by sunlight, specifically UVB radiation.
2. Identify the precursor molecule in the skin involved in this process, which is 7-dehydrocholesterol, a cholesterol derivative present in the skin layers.
3. Recognize that when the skin is exposed to UVB light, 7-dehydrocholesterol undergoes a chemical transformation to form previtamin D3, which then spontaneously isomerizes to vitamin D3 (cholecalciferol).
4. Note that this vitamin D3 then enters the bloodstream and undergoes further activation steps in the liver and kidneys to become the biologically active form of vitamin D.
5. Distinguish this process from other skin functions mentioned, such as retinol conversion, intrinsic factor secretion, or bile acid production, which are not involved in vitamin D synthesis.