The lack of an essential nutrient in the diet produces a state of malnutrition, and chronic malnutrition leads to a characteristic deficiency disease (see Table 50.2). We discussed kwashiorkor (protein deficiency) and scurvy (vitamin C deficiency). Another deficiency disease, beriberi, was directly involved in the discovery of vitamins.

Beriberi, which means “extreme weakness,” became prevalent in Asia in the nineteenth century when it became standard practice to mill rice to a white polish and discard the hulls present in brown rice. A critical observation was that chickens and pigeons developed beriberi-like symptoms when they were fed only polished rice. In 1912 Casimir Funk, a Polish scientist working in England, cured pigeons of beriberi by feeding them discarded rice hulls.

At the time of Funk’s discovery, all diseases were thought either to be caused by microorganisms or to be inherited. Funk suggested that beriberi and some other diseases are dietary in origin and result from deficiencies in specific substances. Funk coined the term “vitamines” from “vital amines” because he mistakenly thought that all these substances vital for life were compounds with amine groups. In 1926 thiamin (vitamin B₁)—the substance lost in the rice milling process—was the first vitamin to be isolated in pure form.

Deficiency diseases can also result from an inability to absorb or process an essential nutrient even if it is present in the diet. Vitamin B₁₂ (cobalamin), for example, is present in all foods of animal origin. Since plants neither use nor produce vitamin B₁₂, a strictly vegetarian diet (not supplemented with dairy products or vitamin pills) can lead to a B₁₂ deficiency disease called pernicious anemia, characterized by a failure of red blood cells to mature. The most common cause of pernicious anemia, however, is not a lack of vitamin B₁₂ in the diet but an inability to absorb it. Normally cells in the stomach lining secrete a peptide called intrinsic factor that binds to vitamin B₁₂ and makes it absorbable by the small intestine. Conditions that damage the stomach lining, such as alcoholism or gastritis, can thus lead to pernicious anemia.

Inadequate mineral nutrition can also lead to deficiency diseases. Examples are hypothyroidism and goiter resulting from iodine deficiency (see Key Concept 40.4), and anemia resulting from iron deficiency. Iodine deficiency is almost unheard of in the developed world because we add iodide to salt. However, it is still a major health problem in large segments of the human population.