Effects of levothyroxine therapy on bone mineral density and bone turnover markers in premenopausal women with thyroid cancer after thyroidectomy

Introduction: We investigated the impact of long-term levothyroxine (LT4) treatment on bone mineral density (BMD) and bone turnover markers (BTMs) in premenopausal women with differentiated thyroid cancer (DTC) after thyroidectomy. Material and methods: Sixty-five premenopausal women who received LT4 therapy at least one year (range, 1.5–9.0 years) after thyroidectomy for DTC and 50 premenopausal women without thyroid diseases were enrolled in this study. We measured the Z-scores of lumbar and hip BMD, serum free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), intact parathyroid hormone (iPTH), N-terminal propeptide of type 1 N procollagen (P1NP), C terminal telopeptide of type 1 collagen (CTX-1), calcium (Ca), phosphorus (P), vitamin D3, and alkaline phosphatase (ALP) in all participants. Results: In DTC subjects, serum TSH levels were lower, and serum FT4, P1NP, CTX-1, and ALP levels were higher compared with controls. The prevalence of low BMD was higher in DTC subjects than in controls. Multivariate logistic regression analysis showed that serum TSH levels were negatively associated with CTX-1 and ALP. Conclusions: We found a high prevalence of low BMD among premenopausal women who received long-term LT4 therapy for DTC after thyroidectomy. Long-term TSH suppression therapy was a significant risk factor for decreased bone strength, mainly by increasing bone turnover.