Which vitamin deficiency is characterized by the clinical triad of dermatitis, diarrhea, and dementia, collectively known as the '4 Ds'?

Explanation

## Niacin Deficiency: Pellagra **Key Point:** Niacin (vitamin B3) deficiency causes pellagra, a disease characterized by the classic '4 Ds': dermatitis, diarrhea, dementia, and death (if untreated). ### Clinical Features | Feature | Details | |---------|----------| | **Dermatitis** | Symmetric, photosensitive rash on sun-exposed areas (face, neck, hands, feet); often described as "glove and stocking" distribution | | **Diarrhea** | Mucosal inflammation of GI tract; may be severe | | **Dementia** | Neuropsychiatric manifestations: confusion, memory loss, personality changes, psychosis | | **Death** | Occurs if deficiency is prolonged and untreated | ### Biochemical Basis **High-Yield:** Niacin is a precursor for NAD^+^ and NADP^+^, essential cofactors in oxidative metabolism. Without adequate niacin, cellular energy production is severely impaired, affecting high-metabolic tissues (skin, GI mucosa, nervous system) first. ### Epidemiology in India Pellagra is rare in India today due to fortification of staple grains, but historically occurred in populations dependent on unfortified maize as a primary carbohydrate source. Risk factors include: - Chronic alcoholism (impaired absorption and metabolism) - Malabsorption syndromes - Carcinoid syndrome (tryptophan diverted to serotonin, reducing niacin synthesis) **Mnemonic:** **PELLAGRA** = **P**hotosensitive dermatitis, **E**nteric diarrhea, **L**oss of memory (dementia), **L**ethal if untreated, **A**lcoholism (common cause), **G**I symptoms, **R**ash on exposed skin, **A**vitaminosis B3. ### Treatment Niacin supplementation (50–500 mg daily depending on severity) rapidly reverses symptoms if caught before irreversible neuronal damage occurs. [cite:Park 26e Ch 8]