A 55-year-old male patient with carcinoid syndrome undergoes workup. Carcinoid tumors divert tryptophan toward serotonin synthesis, leaving little tryptophan for niacin synthesis. The patient develops a dermatitis that worsens on sun-exposed areas, diarrhea, and dementia. Which vitamin's deficiency is classically described by the mnemonic '4 Ds'?

• A Vitamin B6 (pyridoxine)
• B Vitamin B2 (riboflavin)
• C Vitamin B1 (thiamine)
• D Vitamin B3 (niacin) ✓

Explanation

Pellagra results from niacin (vitamin B3) or tryptophan deficiency and is classically remembered by the '4 Ds': Dermatitis (photosensitive, Casal's necklace on the neck), Diarrhea, Dementia (later Delirium), and Death if untreated. Niacin is synthesized from tryptophan (60 mg tryptophan → 1 mg niacin); carcinoid tumors consume tryptophan for serotonin, precipitating pellagra. NAD+ and NADP+ are derived from niacin; their deficiency impairs hundreds of redox reactions.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.