EFFECT OF SMALL IODINE SUPPLEMENTS ON THYROID FUNCTION IN NORMAL INDIVIDUALS.

Supplements of potassium iodide of 100, 200 and 800 μg daily were administered to normal persons over a 12-week period. The plasma inorganic iodine (PII) rose and the thyroid clearance fell. The fall in the thyroid clearance, even at the end of the 12-week period, was not sufficient to compensate for the rise in PII, and so the net result was a small increase in the absolute iodine uptake. It has been calculated that this would result in an average extra 7 mg of iodide taken up over the 12-week period. There was no evidence of an increase in the amount of thyroid hormone secreted, and it is concluded that, as the plasma inorganic iodine level rises, iodide utilization by the thyroid becomes less complete.