Pellagra (niacin deficiency)
A disease caused by severe lack of vitamin B3 (niacin), remembered by the 'three D's': dermatitis, diarrhoea and dementia. Once common where maize-based diets predominated, it is now seen mainly with alcohol dependence, malabsorption or severe malnutrition, and it responds quickly to niacin.
What it is
Pellagra develops when the body lacks enough niacin (vitamin B3) — and the tryptophan the body can convert into it — to make the coenzymes NAD and NADP, which are essential for energy metabolism and countless cellular reactions. Historically it was a widespread disease of populations reliant on maize, because the niacin in maize is bound and poorly absorbed unless the grain is treated with lime (as in traditional tortilla preparation). Today, in well-fed countries it is uncommon and tends to arise from alcohol dependence (the leading cause), malabsorption (such as bowel disease or after gut surgery), severe restrictive diets or eating disorders, certain medicines, and rare inherited disorders that impair tryptophan handling (Hartnup disease) or divert it (carcinoid syndrome). The classic picture is the 'three D's': dermatitis — a symmetrical, reddened, later thickened and pigmented rash on sun-exposed skin (hands, forearms, neck, face); diarrhoea and other gut symptoms; and dementia — confusion, memory loss, apathy and mood change. Left untreated it can progress to a fourth 'D', death. Pellagra is confirmed largely on the clinical picture and dietary history, supported by response to treatment, and it improves dramatically with niacin replacement, usually alongside correcting other nutritional deficiencies.
Key lab markers
- Niacin (vitamin B3) — low; though the diagnosis is largely clinical and niacin is rarely measured directly.
- Urinary niacin metabolites — can support the diagnosis where available.
- Other B vitamins (B2, B6, folate) — often low too, as deficiencies cluster.
- Albumin and general nutrition markers — reflect the underlying malnutrition.
- Response to niacin replacement — rapid improvement supports the diagnosis.
Symptoms
- A symmetrical, sun-exposed rash (hands, forearms, neck 'Casal's necklace', face) that reddens then thickens and darkens
- Diarrhoea and other digestive upset
- A sore, red tongue and mouth
- Confusion, memory problems, apathy, irritability or depression
- Tiredness and weakness
- Poor appetite and weight loss
Related symptoms
When to discuss with a doctor
Pellagra needs prompt medical attention because it responds quickly and completely to treatment, but can progress to serious neurological decline and even death if ignored. Suspect it when a symmetrical, sun-exposed rash appears together with digestive upset and changes in memory, mood or thinking — especially in someone with alcohol dependence, a bowel condition affecting absorption, or a very restricted diet. It is treated with niacin replacement, usually with other B vitamins and attention to the underlying cause and overall nutrition. Mediora.AI can surface a low niacin and the clustering of other low B vitamins that point toward this pattern, but confirming pellagra and starting treatment belongs with your doctor — and neurological symptoms or a rapidly worsening rash should be assessed without delay.