Which vitamin deficiency is associated with carcinoid syndrome?

• A. Vitamin A
• B. Vitamin D
• C. Niacin (B3)
• D. Vitamin C

Answer: (C)

Carcinoid syndrome is associated with a deficiency in niacin (Vitamin B3) primarily because of the altered metabolism that occurs in patients with carcinoid tumors. These tumors often secrete high levels of serotonin, which can be derived from tryptophan. As the body utilizes tryptophan to produce serotonin, there is reduced availability of tryptophan for the synthesis of niacin.

Niacin is synthesized from tryptophan in the body, but when tryptophan is diverted for serotonin production, the levels of niacin can drop significantly, leading to a deficiency. This is clinically significant, as niacin deficiency can result in symptoms consistent with pellagra, including dermatitis, diarrhea, and dementia.

While other vitamin deficiencies may have clinical implications, they do not have the same direct relationship with the altered tryptophan metabolism seen in carcinoid syndrome. Thus, the understanding of this biochemical pathway is key to recognizing why niacin deficiency is particularly relevant to carcinoid syndrome.