Severe niacin (vitamin B3) deficiency causes pellagra — historically known as the disease of the 'four Ds': dermatitis, diarrhea, dementia, and (if untreated) death. Pellagra is now extremely rare in the US thanks to grain fortification, but mild inadequacy persists in some populations, and pellagra still appears in alcoholics, people with malabsorption, and certain medical settings.
Memory loss, confusion, or dementia (in severe cases)
Depression, anxiety, irritability
Loss of appetite
At-risk groups
People with alcohol use disorder (most common cause of pellagra in developed countries)
People in resource-limited settings with corn/maize-dominant diets
People with anorexia or severely restricted diets
People with carcinoid syndrome (tryptophan diverted to serotonin synthesis)
People taking isoniazid for tuberculosis (interferes with niacin synthesis)
People with Hartnup disease (rare hereditary tryptophan absorption disorder)
People with malabsorption conditions (Crohn's, celiac, post-bariatric surgery)
Long-term users of certain medications (5-fluorouracil, pyrazinamide)
When to see a doctorA symmetric rash on sun-exposed skin combined with diarrhea and cognitive changes (the classic 'three Ds') in any at-risk person warrants urgent medical evaluation. Pellagra is rapidly reversible with treatment but fatal if ignored.