Corn protein, or zein, lacks the active form of niacin and the essential amino acid tryptophan, which the body can convert to niacin. During the early part of the 20th century, malnutrition in the United States was common, especially in the southern United States, where diets of sharecroppers, tenant farmers, and their families consisted of mainly corn. Pellagra, characterized by dermatitis, diarrhea, and dementia owing to niacin deficiency, affected at least 3 million Americans, and thousands died from this nutritional disease.