Objective:

To investigate the associations between thyroid hormones, their sensitivity indices, volumetric BMD, and vertebral fracture risk among primary osteoporotic individuals aged over 50 years in northern China, highlighting the significance of these associations in the context of existing literature.

Key Findings:

• The vertebral fracture group had significantly higher TT3 levels and lower TT4 levels compared to the non-fracture group, indicating a potential biomarker for fracture risk.
• Elevated TT3 was independently associated with increased lumbar fracture risk, suggesting a need for monitoring in clinical settings.
• TSH showed a significant positive association with lumbar QCT-BMD, indicating its potential protective role.
• FT4/FT3 and FT3 were positively associated with lumbar QCT-BMD but exhibited a nonlinear negative association in RCS analysis, warranting further investigation.
• Significant interaction effects between FT4/FT3 and lumbar QCT-BMD were observed in gender-specific and age-specific analyses, highlighting the complexity of these relationships.

Interpretation:

Thyroid hormones, particularly FT3, TT3, TSH, and the sensitivity index FT4/FT3, are associated with vertebral fracture risk and bone mineral density, with stronger associations observed in volumetric BMD measured by QCT, emphasizing their potential role in clinical assessments.

Limitations:

• The study is limited to a specific population in northern China, which may affect generalizability; further studies in diverse populations are needed.
• The cross-sectional design limits causal inferences, suggesting the need for longitudinal studies to establish causality.

Conclusion:

The findings suggest that thyroid hormones and their sensitivity indices may serve as indicators of bone mass and fracture risk in the studied population, highlighting the importance of these markers in future research and clinical practice.