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The effect of small increases in dietary iodine on thyroid function in euthyroid subjects
T Paul1, B Meyers, R J Witorsch
1Department of Medicine, University of Massachusetts Medical School, Worcester 01605.
Metabolism: Clinical and Experimental
|February 1, 1988
Summary
High iodine intake in the US may subtly affect thyroid function. Even small supplemental iodine increases can alter thyroid hormone levels and TSH response in healthy individuals.
Area of Science:
- Endocrinology
- Nutritional Science
- Thyroid Research
Background:
- Dietary iodine intake in the United States often exceeds requirements for normal thyroid function.
- Pharmacologic iodine doses (10-1,000 mg/day) in euthyroid individuals cause minor reductions in serum thyroxine (T4) and triiodothyronine (T3) with a compensatory rise in thyroid-stimulating hormone (TSH).
Purpose of the Study:
- To investigate the effects of smaller, more physiologically relevant increases in iodine intake on pituitary-thyroid function.
- To determine the threshold of supplemental iodine that impacts thyroid hormone regulation.
Main Methods:
- Normal volunteers were administered 1,500, 500, or 250 micrograms (mcg) of supplemental iodine daily for 14 days.
- Serum concentrations of T4, T3, and TSH were measured, along with the TSH response to thyrotropin-releasing hormone (TRH).
Main Results:
- A daily intake of 1,500 mcg iodine led to small but significant decreases in serum T4 and T3 levels.
- The 1,500 mcg/day group also exhibited a slight increase in basal TSH and an augmented TSH response to TRH.
- No significant changes in pituitary-thyroid function were observed with 500 mcg or 250 mcg daily iodine supplementation.
Conclusions:
- Even modest increases in dietary iodine, such as 1,500 mcg/day, can induce subtle alterations in thyroid function, likely by inhibiting thyroid hormone release.
- Lower supplemental iodine doses (500 mcg and 250 mcg daily), achievable under normal dietary conditions, did not demonstrably affect pituitary-thyroid function in euthyroid subjects.