THE EFFECTS OF PROLONGED INCREASED IODINE FEEDING1

The effects of adding supplemental iodine to the diet of man and of animals has long been a matter of controversy. As a result its advisability has been questioned. Consequently we welcomed a recent opportunity to investigate this problem.2 A valuable herd of high milk-producing Brown Swiss dairy cows in New York State had been fed a relatively high iodine supplement for a period of approximately three years. Extra iodine had been given as potassium iodide, in fish meal and in kelp, and as forage crops grown on soil fertilized by iodine-containing substances. Since in the past a number of studies on the effects of iodine feeding have been conducted upon an empirical basis, it seemed of importance to us actually to determine the amount of iodine consumed daily, also the daily excretion of iodine in the urine, feces and milk. In addition the blood iodine was determined