—We thank Dr Krakauer for his comments. Dr Krakauer suggests that suppression of PTH may be the mechanism of action for the skeletal effects of excess thyroid hormone. Unfortunately, we were unable to obtain PTH levels and are unable to test this interesting hypothesis. The exact pathophysiology of bone loss with excess thyroid hormone remains to be elucidated.Although the exact mechanism of bone loss in menopause is also in dispute, ovarian failure impairs calcium balance and triggers changes in the bone remodeling cycle in favor of bone resorption. With increased bone resorption, PTH levels may be decreased causing decreased 1,25-dihydroxyvitamin D3 and decreased intestinal absorption of calcium.1 Since lower PTH levels may be associated with estrogen deficiency alone, parathyroid function is probably not the entire explanation for control of bone remodeling.
Thyroid Hormone Use and Bone Mineral Density-Reply. JAMA. 1994;272(23):1822. doi:10.1001/jama.1994.03520230032030