The Relationship of Pellagra to Corn and the Low Availability of Niacin in Cereals

Summary

The poorest inhabitants of an area generally eat the narrowest range of foods, and one staple (which serves as a cheap source of calories) dominates. In turn, the specific type of malnutrition seen in that area depends upon that predominant staple and how it is processed before consumption.

Corn, used here in the sense of “Indian corn” or maize, was brought to Europe from America, and over the period 1750–1850 became the typical peasant’s staple in many of the areas bordering the Mediterranean. By the end of that period, it had also come to be recognized that pellagra had become a serious, chronic disease in these same countries, flaring up each spring amongst the poorest people living on diets containing much corn and very little animal food (i.e., meat, eggs or dairy products) or wine and being generally in a state of wretchedness. Nothing of the sort was seen in areas where wheat and rice were the staple foods, even when they were highly milled.

Most scientists agreed on this association with corn, though not on what was the true cause-and-effect relationship. Research in the present century has shown that pellagra is primarily due to a dietary deficiency of niacin. However, the niacin content of different foods did not tie in well with their pellagra-preventive value. But then it was discovered that a second nutrient, tryptophan, could act as precursor of the vitamin with approximately one sixtieth of the activity of the actual vitamin. The “niacin equivalent” values of foods (calculated from their content of both nutrients) show a much better correlation with their pellagra-preventive value. Thus, mature corn is lower in niacin content than are wheat and rice; also the mixed proteins of corn are lower in their tryptophan content.

What is not explained by the calculation of “niacin equivalent” is the general freedom from pellagra of the peasants in Mexico and Central America, where corn has been the staple for millenia and where poverty, the consequent lack of animal foods in the diet, and general misery, have been fully equal to the conditions in Europe.

It has been known for 40 years that analytical values for the niacin content of foods depended greatly on the method of extraction used, with the highest values being obtained after treatment with alkali. We have confirmed with rat growth assays that the niacin in corn, wheat and rice is only about one-third available to this species, even after ordinary cooking at neutral pH. Cooking corn to make the traditional “tortillas” with calcium hydroxide resulted in all the niacin becoming available. Though some was leached out at the soaking stage, the net niacin value of the corn was still significantly improved.

A concentrate of “bound niacin” prepared from wheat bran, using a procedure developed by Kodicek and Mason at Cambridge, was estimated to be about 25% available to humans. The assay was based on the level of extra urinary metabolites, N¹-methyl-nicotinamide and N¹-methyl-2-pyridone-5-carboxamide after test doses of the preparation. The same preparation treated with calcium hydroxide before dosing was apparently about 70% available as compared with a standard of nicotinic acid.

We are planning more human studies with corn products cooked in different ways. It appears that the traditional processing may have been a crucial factor in making corn a safe staple, while its significance went unrecognized by Europeans.

[The references marked “*” have been reproduced whole or in part, and in English translation where necessary, in Carpenter (1981b)]