American Journal of Clinical Nutrition, Vol 3, 215-224, Copyright © 1955 by The American Society for Clinical Nutrition, Inc.

The Human Requirement for Iodine

¹ From the New York University College of Medicine, New York, N. Y.

The literature relating to the iodine requirements of humans has been reviewed. It has been found that the analytical methods used were poor, that little care, if any, had been taken to insure quantitative correction of the excreta, and that the hourly excretion of iodine in the urine during the night had, without justification, been taken as the same as during the day. However, taking the data for what they may be worth, the variation in the urinary iodine in both goitrous and nongoitrous regions was tremendous, with so much overlapping that it is impossible to conclude that there is any consistent and regular difference between the two.

Apparently, equilibrium has been obtained quite frequently, with an intake no greater than from 50 to 75 µg of iodine per day. This amount has been exceeded frequently by the intake, or excretion, in goitrous regions, even with total exclusion of all seafood.

Experiments with diets of purified constituents showed that rats and mice could grow and have small thyroids with intakes of less than 15 µg of iodine per 3000 calories. This value (15 µg) is of the order of the excretion by fasting men.

The decreases in the incidence of goiter that have followed the introduction of iodized salt have been paralleled or exceeded many times and in many places without any known change in the intake of iodine or any reason to believe that there had been any.

Even if it be conceded that the use of iodized salt has been responsible for a reduction in the incidence of goiter, one may not regard the amount of iodine so furnished as the requirement. To do this would resemble the setting of the requirement for iron as the amount required to cure hypochromic anemia or as the amount required to prevent anemia in severe infestation with hookworm. It is worse, for the excess of iron is probably harmless and the excess of iodine frequently is not.

It would seem, therefore, that in spite of a large number of clinical and animal investigations, the human requirement for iodine has not been finally established.

However, it appears to be small, less than 100 µg per day, and there is no satisfactory evidence that the customary diet, anywhere in the world, does not furnish an adequate amount.