Background~Thyroid hormone is a key regulatory hormone for other physiological systems, including the skeleton. Previous studies have suggested that SCTD may be associated with deleterious skeletal effects. However, controversy persists on the clinical relevance of SCTD as well as on optimal thresholds for treatment. Available data have substantial limitations: 1) limited prospective data are available to assess the associations between SCTD and non-cardiovascular outcomes, such as fractures 2) lack of data from large RCTs to investigate the pathophysiological mechanisms of associations.~Objective~To examine, within a large RCT of elderly participants with subclinical hypothyroidism (the TRUST trial), the impact of thyroxine therapy on the association between SCTD and skeletal fragility, bone mineral density (BMD), bone loss and metabolism, and the risk of fractures.~Methods~The existing trial infrastructure (TRUST thyroid trial-Euresearch FP7,clinicaltrials.gov ID: NCT01660126) will be utilized to collect biospecimens from the 145 Swiss participants with persistent subclinical hypothyroidism randomized to either thyroxine or placebo in Bern and in Lausanne. The assessment is performed by means of dual energy X ray absorptiometry (DXA) and peripheral quantitative computed tomography (pqCT) as a novel bone imaging technique at baseline, and at 1 year of follow-up. In parallel, bone turnover markers in the blood plasma will be measured at baseline and at 1 year of follow-up.
Thyroid hormone is a key regulatory hormone for a range of physiological systems, including the skeleton. Previous studies have suggested that subclinical thyroid dysfunction (SCTD) may be associated with deleterious skeletal effects. However, controversy persists on the clinical relevance of SCTD as well as on optimal thresholds for treatment. Available data have substantial limitations: 1) limited prospective data are available to assess the associations between SCTD and non-cardiovascular outcomes, such as fractures 2) lack of data from large RCTs to investigate the pathophysiological mechanisms of associations between thyroid hormone and bone loss. The aim of the study is to examine the relationship between subclinical hypothyroidism and thyroid hormone replacement in regard to skeletal fragility, bone mineral density (BMD), bone loss and metabolism, and the risk of fractures in elderly participants. The listed parameters will be assessed by dual energy X ray absorptiometry (DXA) and novel bone imaging techniques at baseline, at 1 year of follow-up. The study will be nested in the TRUST trial (clinicaltrials.gov ID: NCT01660126), and will make use of its study infrastructure to determine bone biomarkers from biospecimens at baseline, and at 1 year of follow-up from 145 Swiss participants with persistent subclinical hypothyroidism randomized to either thyroxine or placebo in Bern and Lausanne.