Study of the Impact of Thyroxine Therapy on Bone Turnover Markers in Primary Hypothyroidism: A Cross-Sectional Comparative Study

Introduction Hypothyroidism affects skeletal metabolism. Thyroid hormones regulate bone remodeling, and their deficiency may alter bone turnover markers (BTMs), increasing the risk of osteoporosis. Levothyroxine therapy restores euthyroid status, but its impact on bone metabolism requires further evaluation. Aim This study aims to evaluate the effect of levothyroxine therapy in hypothyroidism on thyroid function and bone turnover markers (C-terminal telopeptide of type I collagen (CTX) and procollagen type I N-terminal propeptide (P1NP)). Methods This cross‑sectional comparative study included 150 participants who were further categorized into three groups: Group I (treated hypothyroidism, n=50), Group II (newly diagnosed untreated hypothyroidism, n=50), and Group III (healthy controls, n=50). Baseline clinical data, thyroid function tests (thyroid-stimulating hormone (TSH), total thyroxine (T4), and total triiodothyronine (T3)), and bone turnover markers (serum CTX and P1NP) were measured. For statistical evaluation, chi‑square and one‑way analysis of variance (ANOVA) tests were used, with p<0.05 considered significant. Results Group II showed significantly elevated TSH (12.8±4.6 mIU/mL) with reduced T4 and T3 compared to Groups I and III (p<0.001). Serum CTX was highest in Group II (0.48±0.12 ng/mL) versus Group I (0.32±0.08 ng/mL) and Group III (0.28±0.07 ng/mL) (p<0.01). Similarly, P1NP was elevated in Group II (62±15 ng/mL) compared to Group I (45±12 ng/mL) and Group III (40±10 ng/mL) (p<0.01). Conclusion Untreated hypothyroidism is found to be linked to more bone resorption and compensatory bone formation, while long‑term levothyroxine therapy normalizes thyroid function and stabilizes bone turnover markers. Early treatment and monitoring of BTMs may help prevent skeletal complications in hypothyroid patients.