Deficiency diseases such as pellagra and beriberi were diagnosed. Carcinoid syndrome thus may produce niacin deficiency and clinical manifestations of pellagra. A deficiency of niacin leads to a disease called pellagra. Niacin deficiency, also known as pellagra, is associated with dermatitis, dementia, and diarrhea. Vitamin B3 deficiency (pellagra) can cause glossitis. Nicotinamide is the preferred treatment for pellagra, caused by niacin deficiency. Some conditions can prevent the absorption of dietary niacin or tryptophan and lead to pellagra. Nixtamalization makes the niacin nutritionally available and prevents pellagra. Hartnup disease is a deficiency of the tryptophan amino acid transporter, which results in pellagra. The excessive loss of tryptophan from malabsorption was the cause of the pellagra like symptoms. As a supplement, it is used by mouth to prevent and treat pellagra (niacin deficiency). Hartnup disease is a genetic disorder that reduces tryptophan absorption, leading to pellagra. Acanthosis nigricans should be distinguished from the casal collar appearing in pellagra. The pellagra epidemic lasted for nearly four decades beginning in 1906. In the 1920s, vitamin B was thought to be the factor necessary for preventing pellagra.