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

Summary 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.