[The risk factors and bone mineral density in women on long-term levothyroxine treatment]

It is controversial if the long-term treatment with thyroid hormone given at substitutive or suppressive doses has a negative effect on bone metabolism. In previous reports the lack of ultrasensitive TSH assays and densitometers with adequate precision, and the heterogeneity of the patients analyzed could explain these discordant results.

We have assessed bone mineral density (BMD) in 43 premenopausal and 53 postmenopausal women, who underwent near total thyroidectomy and I-131 ablation due to differentiated thyroid cancer, that have been followed up (mean duration, 75.5 [43] months) with suppressive thyroid hormone treatment (mean dose, 170 [42] micrograms) in our hospital. Patients with history of hyperthyroidism were excluded. Lumbar BMD (L2-L4) and BMD in three different sites of hip were measured (dual X-ray densitometry) to determine the contribution of several clinical and risk factors associated with thyroid hormone therapy given to BMD.

We have not found significant decrease in BMD at spine or hip when patients were compared with healthy, age and sex matched. Age (inverse correlation) and weight (direct correlation) were the variables mostly influencing BMD). Histologic type of thyroid neoplasia, doses of thyroid hormones, thyroid hormone levels and duration of follow-up, were not associated with changes in BMD. A decrease in calcium intake in postmenopausal and less physical activity in premenopausal women were related with a decreased lumbar BMD.

During long-term treatment of female patients with thyroid hormones, other risk factors should be studied in order to prevent possible loss of bone mass.