There is growing evidence that thyroid function affects bone metabolism and even fractures risk. However, little is known about the relationship between thyroid sensitivity and osteoporosis and fractures. Therefore, we explored the relationship between thyroid sensitivity-related indices and bone mineral density (BMD) and fractures in euthyroid US adults.In this cross-sectional study, 20,686 subjects from National Health and Nutrition Examination Survey (NHANES) data were extracted and analyzed during 2007 to 2010. A total of 3403 men and postmenopausal women aged 50 years or older with available data on diagnosis of osteoporosis and/or fragility fractures, bone mineral density (BMD) and thyroid function, were eligible. TSH index (TSHI), thyrotrophin T4/T3 resistance index (TT4RI/TT3RI), Thyroid feedback quantile-based index (TFQI), Parametric TFQI (PTFQI), free triiodothyronine to free thyroxine ratio (FT3/FT4), the secretory capacity of the thyroid gland (SPINA-GT) and the sum activity of peripheral deiodinases (SPINA-GD) were calculated.FT3/FT4, SPINA-GD, FT4, TSHI, TT4RI, TFQI and PTFQIFT4 were significantly correlated with BMD (P < 0.001). Multiple linear regression analysis showed that FT3/FT4 and SPINA-GD was significantly positively associated with BMD, while FT4, TSHI, TT4RI, TFQI and PTFQIFT4 were negatively associated with BMD (P < 0.05 or P < 0.001). In logistic regression analysis, the odds ratio (OR) for osteoporosis of TSHI, TFQI and PTFQIFT4 were 1.314(1.076, 1.605), 1.743(1.327, 2.288) and 1.827(1.359, 2.455) respectively, and were 0.746(0.620, 0.898) for FT3/FT4 (P < 0.05).In elderly euthyroid individuals, impaired sensitivity to thyroid hormones correlates to osteoporosis and fractures, independent of other conventional risk factors.© 2023. The Author(s), under exclusive licence to Italian Society of Endocrinology (SIE).