A slightly suppressive dose of L-thyroxine does not affect bone turnover and bone mineral density in pre- and postmenopausal women with nontoxic goitre.

There are controversial reports on the potential role of L-thyroxine administration as a risk factor for osteoporosis. We studied bone mass and metabolism in a homogeneous series of 50 Caucasian women, 25 premenopausal and 25 postmenopausal, having nontoxic goitre treated with slightly suppressive L-thyroxine doses (50-200 micrograms/day) with subnormal serum TSH and normal thyroid hormone levels. These patients were matched with 50 controls for age, sex, body mass index, menopausal and thyroid disease. Patients and controls were also investigated for minor determinants of bone loss, such as hereditary and life-style factors. Patients and controls filled in a questionnaire and underwent physical examination, routine laboratory tests and calciotropic and thyroid hormone assay. Bone mineral turnover was evaluated by determining serum osteocalcin, alkaline phosphatase, tartrate-resistant acid phosphatase, calcium, phosphate, urine hydroxyproline/creatinine and calcium/ creatinine ratio. Bone mineral density was measured by dual-energy X-ray absorptiometry at the lumbar spine, femoral neck, trochanter and Ward's triangle. No difference in bone mineral density or biochemical markers was found between patients and controls; bone density and turnover were significantly affected by menopausal status. No relationship between bone density or turnover values and L-thyroxine administration was found. A significant positive correlation was found between osteocalcin and the hydroxyproline/creatinine ratio in premenopausal and postmenopausal patients, but not in controls. Our study suggests that slightly suppressive L-thyroxine administration in nontoxic goitre can activate bone turnover but constitutes neither an actual risk factor for bone loss nor, consequently, for osteoporotic fractures.