Pellagra is caused by –
**Core Concept**
Pellagra is a disease characterized by dermatitis, diarrhea, dementia, and potentially death, caused by a deficiency of niacin (Vitamin B3) or tryptophan in the diet.
**Why the Correct Answer is Right**
The correct answer is **Nicotinic acid deficiency**, which is caused by a lack of tryptophan in the diet. Tryptophan is an essential amino acid that the body can convert into niacin. A deficiency in tryptophan leads to a decrease in niacin production, resulting in pellagra. This is because tryptophan is a precursor to niacin, and niacin is crucial for the production of NAD and NADP, which are essential for energy metabolism.
**Why Each Wrong Option is Incorrect**
**Option A:** A deficiency in vitamin C (scurvy) is a different condition altogether, characterized by collagen synthesis defects and bleeding gums.
**Option B:** A deficiency in vitamin B12 (pernicious anemia) leads to megaloblastic anemia, neurological symptoms, and a risk of dementia, but it does not cause pellagra.
**Option C:** A deficiency in vitamin D (rickets or osteomalacia) affects bone mineralization and calcium homeostasis, but it is not related to pellagra.
**Clinical Pearl / High-Yield Fact**
Pellagra can be prevented by consuming a diet rich in tryptophan, niacin, or a combination of both, as seen in corn-based diets supplemented with niacin.
**Correct Answer:** D.