[Transient thyrotoxicosis induced by Japanese kombu]

Iodine-induced thyrotoxicosis (ITT) has not been reported in Japan. We found that excessive intake of Japanese kombu could elicit ITT. Two Japanese women, 42 and 59 years old, developed thyrotoxicosis one month and one year, respectively, after having eaten foods containing 28-140 mg/day of iodine, calculated from their daily diet. Both patients had high concentrations of serum T3, low ratios of serum T3/T4 or T4/r-T3 compared with untreated Graves' disease, and high concentrations of serum inorganic iodine compared with the mean (M +/- SD: 2.05 +/- 0.99 micrograms/dl) plus 2SD in people eating common foods. Their thyrotoxic signs and symptoms disappeared, and their serum T4, T3, r-T3 and T4/r-T3 normalized one month after the prohibition of kombu intake. To clarify the source of iodine, the iodine content of the kombu and the iodine concentration in water in which the kombu was immersed were measured. Ninety-nine % of the iodine was found in water after 15 min boiling. These findings suggest that a daily intake of more than 28 mg/day of iodine in a diet containing kombu might induce ITT.