Pellagra is caused by deficiency of which vitamin?

**Core Concept**
Pellagra is a disease characterized by the triad of diarrhea, dermatitis, and dementia. It is caused by a deficiency of a specific vitamin that plays a crucial role in the metabolism of amino acids.

**Why the Correct Answer is Right**
The correct answer is **Niacin** (Vitamin B3), which is essential for the synthesis of NAD and NADP from nicotinic acid adenine dinucleotide and nicotinamide adenine dinucleotide phosphate. Niacin deficiency impairs the metabolism of tryptophan, an essential amino acid, leading to the accumulation of toxic compounds that cause the characteristic symptoms of pellagra. The metabolic pathway involves the enzyme kynureninase, which catalyzes the conversion of kynurenine to anthranilic acid.

**Why Each Wrong Option is Incorrect**
**Option A:** Vitamin B1 (Thiamine) is essential for carbohydrate metabolism and the synthesis of coenzyme I, but it is not related to pellagra.
**Option B:** Vitamin B6 (Pyridoxine) is involved in amino acid metabolism, but its deficiency leads to a different set of symptoms, including neurological problems and dermatitis.
**Option C:** Folate is crucial for DNA synthesis and repair, but its deficiency causes megaloblastic anemia, not pellagra.

**Clinical Pearl / High-Yield Fact**
Pellagra is often referred to as the "three Ds" disease, highlighting its classic symptoms of diarrhea, dermatitis, and dementia. This mnemonic can help students remember the characteristic features of the disease.

**Correct Answer: C. Niacin (Vitamin B3)**