Effects of Levothyroxine on Bone Mineral Density, Muscle Force, and Bone Turnover Markers: A Cohort Study

Abstract

Previous studies of the effects of levothyroxine (LT(4)) therapy on bone and bone metabolism have provided conflicting results. This study evaluated the potential effects and dose-response relationship of LT(4) therapy on bone mineral density (BMD) as well as bone and muscle strength. We conducted a prospective, nonrandomized, controlled cohort study with 1.1 ± 0.2-yr follow-up at an academic outpatient clinic in Germany. Ninety-seven men and premenopausal women were enrolled in the study after thyroidectomy and radioiodine remnant ablation for well-differentiated thyroid carcinoma (DTC) or strumectomy for nontoxic goiter. Patients were matched with 89 healthy controls. Twenty-eight men and 46 women on TSH-suppressive doses of LT(4) had DTC, and 23 women were on LT(4) replacement therapy for nontoxic goiter. This study assessed total and trabecular volumetric BMD (vBMD) as well as bone strength at the ultradistal radius, areal BMD at the lumbar spine and both hips, and the grip strength of the nondominant forearm. The dependent variables were annualized rates of change. LT(4) therapy did not impair the areal BMD, bone strength, or grip strength of patients compared with controls. Women with DTC showed a significant loss of total vBMD, whereas men with DTC developed marginally less bone strength than women. Carboxy-terminal telopeptide indicated greater bone resorption in DTC patients compared with controls. There was little evidence of adverse LT(4) effects on bone; however, premenopausal women with DTC might be at risk for reduced vBMD in their ultradistal radii.