Which of the following vitamins can be produced by intestinal bacteria in the human gut?

• A. Vitamin A (retinol)
• B. Vitamin D (cholecalciferol)
• C. Vitamin K (menaquinones)
• D. Vitamin C (ascorbic acid)

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the role of intestinal bacteria in vitamin synthesis. Certain gut bacteria have the ability to synthesize vitamins that the human body cannot produce on its own.
2. Step 2: Review the list of vitamins provided and identify which are typically synthesized by gut microbiota. Vitamins such as Vitamin A, D, and C are generally obtained from diet or sunlight (in the case of Vitamin D).
3. Step 3: Recognize that Vitamin K, specifically menaquinones, is known to be produced by intestinal bacteria in the human gut. This vitamin plays a crucial role in blood clotting and bone metabolism.
4. Step 4: Recall that Vitamin A (retinol) is primarily obtained from dietary sources like liver and carrots, Vitamin D (cholecalciferol) is synthesized in the skin upon sunlight exposure, and Vitamin C (ascorbic acid) must be consumed through diet as humans cannot synthesize it.
5. Step 5: Conclude that among the options, Vitamin K (menaquinones) is the vitamin produced by intestinal bacteria in the human gut.