A 10-month-old infant reared on a soybean product (Mull-Soy®) from birth developed a goiter and hypothyroidism, which was cured by the administration of 4 drops of Lugol's solution and the replacement of the soybean product by whole cow's milk.

After this soybean product was withdrawn but while the patient was still hypothyroid, the thyroid had a high uptake of I131 with rapid discharge into the blood as PBI131. Reinstitution of this soybean product suppressed the thyroidal uptake of I131 and completely inhibited the appearance of PBI131 in the plasma.

Studies in normal adult subjects revealed that this soybean product did not interfere with the absorption of iodine, iodine uptake by the thyroid, oxidation of iodide to iodine or the release of PBI131 in most subjects. Two subjects, however, who had a high plasma level of PBI131 while receiving whole cow's milk had a significant suppression in the PBI131 while receiving this soybean product. This was not associated with a concomitant reduction in the plasma PBI127 thereby indicating that excessive loss of hormonal iodine bad not taken place.

These studies suggested that a goitrogenic agent was present in this particular soybean product, which interfered with thyroid hormone synthesis in susceptible individuals, and which raised the daily requirement for iodine.

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