Suppression of 125I-uptake in mouse thyroid by seaweed feeding: possible preventative effect of dietary seaweed on internal radiation injury of the thyroid by radioactive iodine.

We conducted an animal experiment to determine how dietary seaweeds rich in iodine and dietary fibers suppress radioactive iodine uptake by the thyroid, using mice and four kinds of experimental diets, three with 1% or 2% powdered fronds of the kelp Laminaria religiosa and 2% powdered laver Porphyra yezoensis, and one with cellulose. Iodine content of a hot-water extract of the kelp was 0.530 +/- 0.001%, and its dietary fiber (DF) values were 52.8 +/- 1.2%. Iodine in an extract of the laver was 0.008 +/- 0.001%, and its DF values were 41.4% +/- 0.7%. A statistically significant reduction of 125I uptake by the thyroid, 3 hours after intragastric administration of the radionuclide at a dosage of 18.5 kBq or 185 kBq in 0.3 ml aqueous solution per mouse, was observed in mice previously fed the experimental diets containing 1% and 2% kelp during periods varying from 24 hours to 7 days. The degree of the suppression was observed to depend on the amount of iodine in the diet or in the injected sample, no matter whether organic or inorganic, judging from the results of an additional experiment. Thus, we conclude that previously fed iodine-rich material, especially dietary seaweeds rich in iodine and other minerals, vitamins, and beta-carotene, such as kelps or laver supplemented with inorganic iodine, may be effective in prevention of internal radiation injury of the thyroid.