Nutrition and deficiency diseases: A lack of niacin (vitamin B3) most classically causes which condition characterized by dermatitis, diarrhea, and dementia?

Introduction / Context:
Niacin (vitamin B3) is a precursor for NAD+ and NADP+, essential cofactors in redox metabolism. Deficiency leads to a characteristic clinical triad and historical public health relevance.

Given Data / Assumptions:

• Niacin deficiency arises from poor diet, alcoholism, malabsorption, or Hartnup disease.
• Classical triad: dermatitis, diarrhea, dementia; severe cases may be fatal.
• Contrast with other vitamin deficiencies to avoid confusion.

Concept / Approach:
NAD+/NADP+ participate in glycolysis, TCA cycle, fatty acid metabolism, and biosynthesis. Inadequate niacin disrupts cellular energy and repair, especially in high-turnover tissues (skin, gut, brain), explaining the pellagra triad.

Step-by-Step Solution:
Identify the deficiency: niacin (B3) or tryptophan (a precursor).Relate systemic manifestations to impaired NAD(H)/NADP(H)-dependent reactions.Match with condition: pellagra is the hallmark disease of niacin deficiency.

Verification / Alternative check:
Supplementation with niacin or tryptophan improves symptoms; historical elimination of pellagra followed dietary fortification.

Why Other Options Are Wrong:

• Scurvy: vitamin C deficiency.
• Cataract: multifactorial; not a specific vitamin B3 deficiency label.
• Anemia: may occur in other deficiencies (e.g., folate, B12, iron).

Common Pitfalls:
Confusing pellagra (B3) with beriberi (B1) or pellagra-like photosensitive rash in other metabolic disorders; always check the triad.

Final Answer:
pellagra