Which vitamin is synthesized by the skin upon exposure to sunlight?

• A. Vitamin C
• B. Vitamin B12
• C. Vitamin K
• D. Vitamin D

Answer: (D)

Verified step by step guidance

1. Understand the role of sunlight in vitamin synthesis: Sunlight, specifically ultraviolet B (UVB) radiation, plays a critical role in the synthesis of certain vitamins in the human body.
2. Identify the vitamin synthesized by the skin: The skin synthesizes Vitamin D when exposed to UVB radiation from sunlight. This process begins with the conversion of 7-dehydrocholesterol, a compound in the skin, into pre-vitamin D3.
3. Clarify why other options are incorrect: Vitamin C is obtained from dietary sources like fruits and vegetables, Vitamin B12 is primarily found in animal products and requires intrinsic factor for absorption, and Vitamin K is synthesized by gut bacteria or obtained from leafy greens.
4. Explain the importance of Vitamin D: Vitamin D is essential for calcium absorption and bone health. It also plays a role in immune function and other physiological processes.
5. Summarize the process: Exposure to sunlight triggers the skin to produce Vitamin D, which is then converted into its active form in the liver and kidneys to perform its biological functions.