Thyroid hormones are essential regulators of skeletal remodeling. They affect bone metabolism directly through triiodothyronine (T3) and thyroxine (T4) actions on osteoblasts and osteoclasts, and indirectly via thyroid-stimulating hormone (TSH). Overt hyperthyroidism accelerates bone turnover, causing reduced bone mineral density (BMD) and increased fracture risk. Conversely, hypothyroidism induces a low-turnover state that may preserve or slightly increase BMD but impair bone quality. The effects of subclinical thyroid dysfunction remain controversial and depend on age, sex, vitamin D status, and duration of disease. This study aimed to assess the association between thyroid hormone imbalance and bone metabolism markers in patients with hypo- and hyperthyroidism.

The study was conducted at the Republican Specialized Scientific and Practical Medical Center of Endocrinology named after Academician Y.H. Turakulov (Tashkent, Uzbekistan). Fifty patients were enrolled and divided into two groups: hypothyroidism (autoimmune thyroiditis or nodular goiter, n = 28) and hyperthyroidism (Graves’ disease or toxic adenoma, n = 22). Mean age was 32.9 ± 4.07 years, with female predominance (78.6% and 72.7%). Laboratory tests included serum calcium, 25-hydroxyvitamin D [25(OH)D], and thyroid function parameters (TSH, free T4, free T3, anti-TPO, anti-TSHR). BMD at the lumbar spine (L1–L4) and total hip was measured by dual-energy X-ray absorptiometry (DXA). Statistical analysis was performed using SPSS 25.0 (IBM Corp., Armonk, NY, USA); p < 0.05 was considered significant.

Hyperthyroid patients demonstrated significantly lower BMD than hypothyroid ones: spine 0.85 ± 0.08 g/cm² (T-score −1.8) vs. 0.98 ± 0.06 (−0.4); hip 0.78 ± 0.07 (−1.6) vs. 0.92 ± 0.05 (−0.2). Serum 25(OH)D and calcium were 18.0 ± 6.0 ng/mL and 2.60 ± 0.08 mmol/L in hyperthyroidism vs. 22.5 ± 7.5 ng/mL and 2.25 ± 0.06 mmol/L in hypothyroidism. Differences in BMD were statistically significant (p < 0.05), confirming enhanced bone resorption in hyperthyroidism.

Thyroid hormone dysregulation significantly alters skeletal metabolism. Hyperthyroidism is associated with accelerated bone turnover, reduced BMD, and a greater risk of osteopenia and osteoporosis. In contrast, hypothyroidism is linked to low-turnover bone metabolism, often with preserved or mildly increased BMD but compromised bone microarchitecture and quality. These findings emphasize the need for early evaluation of BMD and vitamin D status in patients with thyroid disorders to prevent long-term skeletal complications.