EFFECTS OF SUPPRESSIVE DOSES OF LEVOTHYROXINE TREATMENT ON SEX-HORMONE-BINDING GLOBULIN AND BONE METABOLISM

The adverse effects of suppressive thyroxine treatment have previously been investigated and conflicting results have been published, This s tudy aimed at evaluating the effects of subclinical hyperthyroidism on the liver and bones, We investigated the action of thyroxine on the l iver by measuring sex-hormone-binding globulin (SHBG) levels and on bo ne turnover by evaluating osteocalcin (BGP) in both pre- and postmenop ausal women, We compared the levels of both proteins to those of untre ated subjects matched for age, menopausal status, and weight, Bone min eral density (BMD) was evaluated by biphotonic absorptiometry only in postmenopausal women with estrogen replacement therapy (ERT) and compa red to two postmenopausal estrogen-treated controls, Forty-five women with multinodular goiter (38) or postsurgical thyroid carcinoma (7) we re studied, They had received LT(4) for 3 to 5 years (150 +/- 34 mu g/ day for nontoxic multinodular goiter, 184 +/- 46 mu g/day for thyroid carcinoma), All patients had normal free T-3 concentrations, No signif icant difference was found in SKBG values between patients and control s whatever the menopausal status and the BMI; a significant increase i n BGP was noted in premenopausal women (9.6 +/- 2.2 vs 6.7 +/- 2.3 ng/ ml; p < 0.0006), No significant BGP and BMD variations were observed i n treated postmenopausal women, In summary, the study of carefully mat ched patients and controls revealed that thyroxine treatment has no ef fect on SHBG levels, The increase in BGP observed in premenopausal wom en might suggest a high turnover bone loss. A deleterious effect on sp ine BMD was not observed in this small group of postmenopausal women, but ERT might be a confounding factor and could also explain the absen ce of variation of BGP in postmenopausal women, However, the long-term impact of this treatment upon bone density has to be thoroughly evalu ated.