NIACIN DEFICIENCY (PELLAGRA)

NIACIN DEFICIENCY (PELLAGRA). Deficiency of the vitamin niacin can result in the disease pellagra. This illness is characterized by the appearance of severe dermatitis on the parts of the skin that have been exposed to the sun, with deep cracking and flaking. Sufferers also have diarrhea and, in many cases, some kind of dementia. The condition typically flares up during spring, as sunshine becomes stronger. In practice, patients were often found to be deficient in the vitamin riboflavin in addition to niacin. Both in the Old and New Worlds, the condition has almost always been confined to people consuming corn (that is, maize) as their staple grain. The explanation is complex. We can synthesize niacin for ourselves to some extent if our diet contains a good supply of the amino acid tryptophan because we have enzymes that can, in a series of steps, turn a portion of any excess tryptophan molecules into niacin. The problem with corn is that the proteins that it contains have an unusually low proportion of tryptophan, and this is insufficient to provide a second source of the vitamin. Mature corn, like the mature grains of other cereals, does contain niacin, but it is mostly present in linkage with other compounds that make it essentially indigestible, because the digestive enzymes in the gut cannot break these linkages. In Central America and Mexico, where corn has been the staple grain for millennia, the populations have learned to soften the grains by soaking them with lime (calcium hydroxide) before grinding them to a paste. It is now realized that, in addition to its softening action, the alkaline lime liberates the niacin from its linkages, so that it is now nutritionally available. This is, at least, a partial explanation for the freedom of these peoples from pellagra. In addition, if a diet rich in maize is supplemented with a diet that also uses beans as a stable, as is the case among the traditional natives of Mexico, then the low level of tryptophan in maize is compensated by the higher tryptophan level in beans. Many types of long-established diets have this type of essential amino acid complementarity among the foods consumed.

However, when corn was brought back to the Old World, and gradually came to be adopted as a staple food in Southern Europe, but without the use of lime in its preparation, pellagra became a serious problem. In the nineteenth century it was suspected that corn developed toxic molds during storage. In France its use as a food crop was made illegal, and in Italy a special class of "pellagra hospitals" was established. In the southern regions of the United States, pellagra became a serious problem from about 1910 onward. There had been no obvious change in dietary habits to explain this, but it is now realized that corn processors had introduced a new method of milling corn that separated the germ. This was advantageous in reducing the oil content of the cornmeal and increasing its storage life, but it further halved the tryptophan content of the meal. The average consumer in the South was using approximately equal parts of cornmeal and of white wheaten flour that was somewhat richer in tryptophan. It appears that the change in milling was just enough to tip the balance toward the appearance of pellagra in those with only low intakes of good supplementary foods such as meat and milk. Niacin is now one of the synthetic vitamins included in the supplements routinely used to enrich flours in many Western countries.

See also Assessment of Nutritional Status; Dietary Assessment; Dietary Guidelines; Food, Composition of; Maize; Malnutrition; Mexico; Nutrients; Nutrition; United States: The South; Vitamins: Overview.

BIBLIOGRAPHY

Carpenter, Kenneth J., ed. Pellagra. Stroudsburg, Pa.: Hutchinson Ross, 1981.

McDowell, L. R. Vitamins in Human and Animal Nutrition. Ames: Iowa State University Press, 2000.

Kenneth John Carpenter