Glucose tolerance and lipid profile in longterm exogenous subclinical hyperthyroidism and the effects of restoration of euthyroidism, a randomised controlled trial.

OBJECTIVE The impact of prolonged subclinical hyperthyroidism on glucose and lipid metabolism is unclear. Therefore, we evaluated glucose and lipid metabolism in patients with differentiated thyroid carcinoma (DTC) on TSH suppressive thyroxine therapy as a model for subclinical hyperthyroidism and investigated whether restoration to euthyroidism affects metabolism. DESIGN We performed a prospective, single-blinded, placebo-controlled, randomised trial of 6 months duration with 2 parallel groups. PATIENTS Twenty-five subjects with a history of differentiated thyroid carcinoma with > 10 years TSH-suppressive therapy with l-thyroxine completed the study. l-thyroxine dose was replaced by study medication containing l-thyroxine or l-thyroxine plus placebo. Medication was titrated to establish continuation of TSH suppression (low-TSH group, 13 patients) and euthyroidism (euthyroidism group, 12 patients). MEASUREMENTS We evaluated glucose metabolism by glucose tolerance test and HOMA (IR) and lipid metabolism by lipid profile. In addition, we measured plasma concentrations of glucoregulatory hormones. RESULTS At baseline, glucose tolerance, HOMA (IR), lipid profile and plasma concentrations of glucoregulatory hormones were within the normal range. No significant differences between the low TSH and euthyroidism group were observed. After 6 months, neither glucose nor lipid metabolism in the low TSH group were different from baseline values. CONCLUSION In summary, glucose and lipid metabolism in patients with DTC and long-term subclinical hyperthyroidism in general are not affected. Restoration of euthyroidism in general does not affect glucose and lipid metabolism.