Effects of levothyroxine suppressive therapy on bone mineral density in premenopausal women

Background: Levothyroxine (L-T4) is widely prescribed for treating thyroid disorders, but its effect on bone mineral density (BMD), is being debated. Objectives: We studied the effect of supraphysiologic doses of L-T4 on BMD in a group of premenopausal women. Patients and methods: We included 50 women (mean age = 36.8 ± 7.6 years) receiving L-T4 for at least 1 year for treating their benign cold thyroid nodules. Serum T3, T4, thyroid-stimulating hormone (TSH), parathyroid hormone (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 dual energy X-ray absorptiometry (DXA). Results: No significant decrease was detected in the bone density of the subjects treated with L-T4 compared with the control group. Conclusion: L-T4 treatment for 1 year is not associated with increased risk of osteoporosis in premenopausal women but other potential adverse effects still need to be monitored in women receiving L-T4 especially long-term.