ZINC SUPPLEMENTATION ALTERS THYROID-HORMONE METABOLISM IN DISABLED PATIENTS WITH ZINC-DEFICIENCY

Objective: We examined zinc (Zn) status in relation to thyroid functio n in disabled persons, because the association between Zn deficiency a nd thyroid function remains controversial. Methods: After measuring se rum free 3,5,3'-triiodothyronine (T-3) and free thyroxine (Ts) in 134 persons, TSH-releasing hormone (TRH) injection test and estimation of Zn status were conducted in persons with low free T-3. Results: Thirte en had low levels of serum free Ta and normal T-4. Patients with eleva ted levels of serum 3,3',5'-triiodothyronine (rT(3)) showed an enhance d reaction of serum thyrotropin (TSH) after TRH injection. Nine of 13 patients had mild to moderate Zn deficiency evaluated by body Zn clear ance and increased urinary Zn excretion. After oral supplementation of Zn sulphate (4-10 mg/kg body weight) for 12 months, levels of serum f ree T-3 and T-3 normalized, serum rT(3) decreased, and the TRHinduced TSH reaction normalized. Serum selenium concentration (Type 1 T-4 deio nidase contains selenium in the rat) was unchanged by Zn supplementati on. Conclusion: Zn may play a role in thyroid hormone metabolism in lo w T-3 patients and may in part contribute to conversion of T-4 to T-3 in humans.