T4 rather than TSH correlates with BMD among euthyroid adults

Area of Science:

• Endocrinology
• Bone Metabolism
• Gerontology

Background:

• Thyroid hormones play a crucial role in regulating metabolism, including bone turnover.
• Understanding the relationship between thyroid hormone levels and bone mineral density (BMD) is essential for assessing fracture risk, particularly in euthyroid individuals.
• Existing research has yielded conflicting results regarding the association between thyroid hormones and bone health.

Purpose of the Study:

• To investigate the association between thyroid hormone profiles and bone mineral density (BMD) in a cohort of euthyroid adults.
• To explore both linear and nonlinear relationships between thyroid hormones and BMD.
• To determine the association of thyroid-stimulating hormone (TSH) and thyroxine (T4) with previous fractures.

Main Methods:

• Cross-sectional analysis of 3,759 euthyroid participants from the National Health and Nutrition Examination Survey (2007-2010).
• Multivariate linear regression models were employed to assess linear associations between thyroid hormones and BMD.
• Generalized additive models and logistic regression were used to characterize nonlinear relationships and assess fracture risk.

Main Results:

• Free thyroxine (FT4), T4, free triiodothyronine (FT3), and total triiodothyronine (T3) showed a negative association with total femur and total spine BMD.
• Subgroup analyses confirmed a consistent negative association between T4 and BMD across different age and gender groups, including those with osteopenia/osteoporosis.
• Nonlinear analyses revealed various curve shapes (U-shaped, inverted U-shaped, L-shaped) between thyroid hormones and BMD, and high-normal T4 levels were linked to increased prevalence of previous fractures.

Conclusions:

• Thyroxine (T4) demonstrates a negative correlation with BMD in euthyroid adults, irrespective of age, gender, or baseline BMD.
• Elevated T4 levels within the normal range are associated with a higher incidence of prior fractures.
• Thyroid-stimulating hormone (TSH) was found to have no significant association with BMD variations or fracture risk in this population.