Assessment of the Musculoskeletal Axis and Body Composition Parameters in Women with Controlled Thyroid Dysfunction: A Cross-Sectional Study

Background: The stability of the musculoskeletal axis is crucial for maintaining mobility in women, yet the impact of controlled thyroid dysfunction on this system remains ambiguous. Objectives: The aim of this cross-sectional study was to compare the body composition and functional performance of women with Hashimoto’s thyroiditis, women with hypothyroidism, and healthy controls in the context of the role of parathyroid hormone (PTH) as a potential comorbid factor. Methods: The study included 70 women divided into three groups: Hashimoto’s thyroiditis (n = 27), hypothyroidism (n = 15), and control (n = 28). Anthropometric parameters, including limb muscle mass (ALM) and bone mineral density (BMD), were assessed using X-ray absorptiometry (DXA). Physical performance was assessed using handgrip strength (HGP) and Timed Up and Go (TUG) tests, supplemented by ELISAs for metabolic and neurotrophic biomarkers (BDNF, irisin, GDF-15, P3NP). Results: The results showed no statistically significant differences between groups in muscle mass (ALM: p = 0.13; ALMI: p = 0.27) or bone density (BMD: p = 0.82). Functional performance outcomes were also comparable between groups (HGP: p = 0.71; TUG: p = 0.143). The levels of the analyzed biomarkers did not differ significantly by thyroid status (BDNF: p = 0.91; irisin: p = 0.85; GDF-15: p = 0.96). Furthermore, correlation analysis revealed that PTH showed a moderate, negative correlation with P3NP in the total population (r = −0.44, p = 0.003). In contrast, its association with muscle mass index (ALM) was attenuated after FDR correction. Conclusions: These preliminary results indicate no detectable deterioration in musculoskeletal and functional parameters in women with managed thyroid dysfunction. However, due to the small sample size of the hypothyroidism subgroup and low statistical power, these findings cannot establish physiological equivalence and must be interpreted with caution, as they do not confirm a direct protective effect of levothyroxine therapy against muscle mass decline.