Pellagra, a disease caused by insufficient intake of niacin, is usually the result of a diet based on cornmeal.
Early signs of deficiency include indigestion, muscular weakness and changes in the texture of the skin.
Full-blown pellagra is characterised by dermatitis (an inflammatory condition of the skin), diarrhoea and changes in the texture and colour of the tongue (known as "beefy tongue"). Confusion and disorientation is usually also experienced by the sick person.
Dermatitis due to niacin deficiency is characterised by cracked, pigmented skin.
People suffering from pellagra usually are severely malnourished in general.