The vitamin produced in the skin that is important for calcium absorption is which?

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

Answer: (D)

Vitamin D is produced in the skin when it’s exposed to ultraviolet B sunlight, and it’s essential for absorbing calcium from the gut. The active form of vitamin D signals the intestines to take up calcium (and phosphate), which is necessary for strong bones and proper mineralization. Without enough vitamin D, calcium absorption drops, leading to weaker bones over time. The other vitamins don’t play this sunlight-activated role in calcium uptake: vitamin C supports collagen and healing, vitamin A is important for vision and cell growth, and vitamin K is involved in blood clotting and some bone processes but isn’t produced in the skin to promote calcium absorption.