Relationship between serum zinc levels, thyroid hormones and thyroid volume following successful iodine supplementation

OBJECTIVE: Zinc is essential for many biochemical processes and also for cell proliferation. Thyroid hormones influence zinc metabolism by affecting zinc absorption and excretion. Additionally, zinc deficiency affects thyroid function. The aim of the present study was to evaluate a possible association of zinc levels with thyroid volume, thyroid hormones and thyroid autoantibody levels in healthy subjects, patients with autoimmune thyroid disease (AITD) and patients with nodular goitre following successful iodine supplementation. This is a cross-sectional study in which 201 subjects who were not under medical treatment and did not have previous thyroid surgery or radio-iodine treatment were evaluated. Seventy patients had nodular goitre, 67 AITD and 64 had normal thyroid. Thyroid volume was calculated by ultrasonographic measurements. Serum free T4, T3, TSH, anti-thyroglobulin and anti-thyroid peroxidase levels were determined by appropriate methodology. RESULTS: In patients with normal thyroid, zinc levels were significantly positively correlated with free T3 levels (p<0.001). In the nodular goitre group, thyroid volume was negatively correlated with TSH and circulating zinc levels (p=0.014 and p=0.045, respectively). In the AITD group, thyroid autoantibodies and zinc were significantly positively correlated. Multiple regression analysis revealed a significant relationship between thyroid volume and zinc only in the patients with nodular goitre (p=0.043). CONCLUSION: There was significant correlation of serum zinc levels with thyroid volume in nodular goitre patients, with thyroid autoantibodies in AITD and with free T3 in patients with normal thyroid.