[Osteopenia and treatment with L-thyroxine]

Thyroid hormones exert potent effects in bone as evidenced by bone loss which accompany untreated thyrotoxicosis. Conventional thyroxine replacement therapy may be associated with some degree of biochemical or tissue hyperthyroidism, increasing the risk for late onset osteoporosis. This has led to recommendations for reductions in L-T4 dosages. More recently, however, other reports have indicated that L-T4 therapy does not have adverse effects on bone mass. The overall analysis of both past and recent published reports has indicated that the evidence that conventional thyroxine therapy has adverse effects on bone mass is hard to ignore, although the magnitude of these effects is likely to be relatively small and closely related to estrogen deficiency.