Deficiency Causes diets low in tryptophan or niacin corn staple diets Hartnup disease ↓ tryptophan absorption in kidneys and small intestine malignant carcinoid syndrome ↑ tryptophan metabolism in production of serotonin INH therapy ↓ vitamin B6 leading to ↓ niacin synthesis Presentation glossitis severe deficiency leads to pellagra (3 D's) diarrhea, dermatitis, dementia Excess Causes nicotinic acid given at high doses as hyperlipidemic treatment Presentation facial flushing due to prostaglandins, treated with aspirin intrahepatic cholestasis