SUPPRESSIVE DOSES OF THYROXINE DO NOT ACCELERATE AGE-RELATED BONE LOSS IN LATE POSTMENOPAUSAL WOMEN

To examine whether suppressive doses of thyroxine have any adverse eff ects on bone, we evaluated various bone metabolic markers (lectin-prec ipitated alkaline phosphatase, osteocalcin, carboxyl-terminal region o f type I Collagen propeptide, tartrate-resistant alkaline phosphatase, and urinary excretion of hydroxyproline and pyridinium crosslinks), i ncidence of vertebral deformity, total body and regional (lumbar spine and radius) bone mineral densities (BMDs), and rates of bone loss in 24 late postmenopausal (more than 5 years after menopause) women who w ere treated with levothyroxine (L-T-4) after total thyroidectomy for d ifferentiated carcinoma, Depending on the clinical records, including serum TSH levels measured by immunoradiometric assay, these patients w ere divided into two groups, One group of patients was given suppressi ve doses of L-T-4 (TSH < 0.1 mU/L, n = 12) and the other group was giv en nonsuppressive doses of L-T-4 (TSH > 0.1 mU/L, n = 12), There was n o difference in bone metabolic markers and incidence of vertebral defo rmity between the groups, In patients with TSH suppression, Z-scores o f BMDs calculated from age-matched healthy women (n = 179, aged 55 to 80) were nearly in the zero range of values (0.077 at total body, 0.22 8 at lumbar spine, and -0.117 at trabecular region of lumbar spine), T he rate of bone loss in TSH-suppressed patients (-0.849 +/- 0.605%/yea r) was not significantly different from that of nonsuppressed patients (-0.669 +/- 0.659), These prospective and cross-sectional data sugges t that long-term levothyroxine therapy using suppressive doses has no significant adverse effects on bone.