Which vitamins are synthesized by gut microbiota in the large intestine?

• A. Vitamin C
• B. Vitamin K and some B vitamins
• C. Vitamins A and D
• D. Vitamin E

Answer: (B)

The key idea is that the colon’s resident microbes can manufacture vitamins that the host can use. In the large intestine, gut bacteria produce vitamin K in the form of menaquinones and also generate several B vitamins, such as biotin (B7) and folate (B9). These microbial vitamins can supplement the body's needs for these nutrients. By contrast, vitamins like C, A, D, and E are not produced in meaningful amounts by gut microbiota and are instead obtained mainly from diet or other tissues. So the vitamins synthesized by gut microbiota in the large intestine are vitamin K and some B vitamins.