Evaluation of the normal range of values for uptake of radioactive iodine by the thyroid gland.

Uptake of radioactive iodine by the thyroid gland after oral administration of 75 muCi was determined in 1971-72 in 60 euthyroid female volunteers from the North Shore of Vancouver. Values were as low as 3% at 4 hours and 7% at 24 hours in subjects otherwise proven to be euthyroid. The highest values found were 13 and 26% at 4 and 24 hours. The effective thyroxine ratios were all within the accepted normal range. However, more than half of the volunteers showed some enlargement of the thyroid gland. These results suggest an increased iodine pool in the subjects, the likley source being iodine in mild, dairy products and erythrosine, a colouring agent in foods and pharmaceutical products. Potassium iodate, used sometimes in bread baking, contributed little to this pool in our sample. Subjects were, on the average, 9 to 25% heavier than their peers 20 years ago.