Effects of levothyroxine suppressive therapy on bone mineral density in pre-menopausal women

BACKGROUND: Levothyroxine (L-T4) is widely prescribed to treat thyroid disorders, its effect on bone mineral density (BMD), however, has remained under debate. Objectives: We studied the effect of supraphysiologic doses of L-T4 on BMD in a group of pre-menopausal women. PATIENTS AND METHODS: We included a number of 50 women (Mean age=36.8±7.6 years) receiving L-T4 for at least one year for their benign cold thyroid nodules. Serum T3, T4, TSH, PTH, Calcium, and Phosphate and urine calcium and sodium levels of all patients were measured. Bone density at femoral neck and lumbar (L1-L4) regions was measured, using DXA (dual energy X-ray absorptiometry). RESULTS: No significant decrease was detected in the bone density values of the subjects in comparison with the control group. CONCLUSION: It can be concluded that L-T4 suppression for one year is not associated with increased risk of osteoporosis in pre-menopausal women. However, it seems necessary to observe other risk factors in women receiving L-T4 especially during a long-term treatment.