Does serum TSH level have thyroid hormone independent effects on bone turnover?

Abstract

Hyperthyroidism-associated bone loss has been attributed to excess of thyroid hormones. Animal studies, however, suggest that TSH deficiency might affect bone turnover independently of thyroid hormones. Here, I discuss the study by Heemstra and colleagues, who assessed the relationship between serum TSH level and markers of bone turnover in patients with thyroid cancer receiving supraphysiological doses of levothyroxine. The effect of thyroid hormones could not be distinguished from that of TSH as the intact hypothalamic–pituitary–thyroid axis maintained the typical inverse relationship between thyroid hormones and TSH. The study included 27 men and 76 premenopausal women, although previous data indicate that suppressive doses of levothyroxine have no effect on BMD in such patients. Accordingly, Heemstra et al. did not identify a relationship between TSH level and BMD. Although mechanisms of thyrotoxicosis-related bone loss remain controversial, postmenopausal women with thyroid cancer who require long-term TSH suppression should be monitored carefully for osteoporosis.