Vitamin deficiency diseases, such as pellagra, rickets, beriberi, night blindness, and scurvy, used to account for an enormous burden of suffering worldwide. One by one, the underlying dietary deficiencies were defined, and, in the early part of the 20th century, the chemical structures of the missing nutrients were identified. While vitamin deficiency diseases remain endemic in some parts of the world, in most regions they have been eliminated by public health programs and improvements in living conditions. These diseases are rarely seen in most countries, except in individuals at increased risk because of unbalanced diets, malabsorption, abnormal losses (eg, hemodialysis), or uncommon genetic defects.