Bone mineral density in premenopausal women receiving levothyroxine suppressive therapy

Osteoporosis is a well-known complication of thyrotoxicosis. Prolonged subc linical hyperthyroidism due to L-thyroxine treatment has been associated wi th reduced bone mass and thus with the potential risk of premature developm ent of osteoporosis. The aim of this study was to assess the effect of a chronic L-thyroxine sup pressive treatment on bane mineral density (BMD) in a group of premenopausa l women. Forty consecutive patients (mean age +/- SE = 40.95 +/- 1.56 years ) affected by non-toxic goiter underwent bone mineral densitometry (dual en ergy X-ray absorptiometry; DEXA) of the lumbar spine (L1-L4) and right femo ral neck. At the time of the study the patients had been under thyroid stim ulating hormone (TSH) suppressive therapy for 74.95 +/- 10.34 months (range 17-168 months). Baseline levels of free thyroxine (fT4), free triiodothyro nine (fT3), TSH, calcium and phosphorus were measured and correlated with B MD. The age of starting, duration of treatment, main daily dose, cumulative dose of treatment and body mass index (BMI) were also correlated with BMD. Statistical analysis was performed by multiple linear regression. BMD amon g female patients war not significantly different from chat of the general population matched for age and sex. With the use of the regression model, n o significant correlation was found between BMD and the variables considere d. In conclusion, our data suggest that L-thyroxine suppressive therapy, if ca refully carried out and monitored, has no significant effect on bone mass.