TG and hyperthyroidism: However, in this study, we found a significantly high prevalence of zinc deficiency in the cases (and especially among those with hypothyroidism or hyperthyroidism compared to those who were euthyroid), contrasting with previously published studies reporting that low zinc diets (or low circulating levels) can cause certain changes in the structure of the thyroid gland and/or in the metabolism of thyroid hormones [7,8,9,22].