Bread iodine content and thyroid radioiodine uptake: a tale of two cities.

The iodine content of bread consumed in the Bronx, New York, was found to be significantly lower than that of bread consumed in Columbia, Missouri. This difference in dietary intake of iodine could account for the lowered range of normal values for 24-hour (131)I uptake tests in Columbia, and the persistence of the same normal range for this test over the past 28 years in the Bronx. A population with high iodine intake requires higher doses of radioactive iodine in the diagnosis and treatment of thyroid disease. Questions are raised regarding the relationship of high iodine intake to the risk of developing thyrotoxicosis.