Serum triiodothyronine,bone turnover,and bone mass changes in euthyroid pre- and postmenopausal women

Summary Hyperthyroidism and thyroid hormone substitutive therapy with serum iT₃ in the normal range of values are known to lead to increased bone remodeling and loss of bone mass. We looked for a relationship between serum iT₃ and bone metabolic or bone mass parameters in 402 euthyroid women aged 44–60. In a group of 93 premenopausal women, a group of 309 postmenopausal women, and a group of 118 untreated postmenopausal women, serum iT₃ was higher in the women classified as having “high” bone turnover according to both alkaline phosphatases and hydroxyprolinuria values. In postmenopausal women, serum iT₃ corrected for thyroid binding globulin (TBG) (T_3c) was higher in those receiving no estrogen replacement therapy. In a longitudinal study (n=131), the rate of changes in lumbar bone mineral content was associated with changes in T_3c. A less favorable bone mass evolution was associated with an increase in serum T_3c, and inversely. Data suggest that the relationship of iT₃/bone metabolism is direct and not merely the consequence of estrogen induced changes in both iT₃ and bone metabolism. iT₃ should be explored at the bone cellular level as a possible mediator in bone metabolic changes occurring in menopause and many other clinical situations.