Thyroid supplements: effect on bone mass.

Thyrotoxicosis and thyroid replacement therapy can cause osteopenia. The relative effects of such therapy and of aging, body size, menopausal status and smoking on bone mass were compared by measuring the combined cortical thickness (CCT) of the second metacarpal bone in 151 women taking thyroid hormone. Age was the single factor strongly related to CCT, with the mean CCT decreasing by 0.045 mm per year. Women who had taken estrogen replacement medications had a higher CCT measurement, while those who used thyroid hormone in a dose of at least 3 grains a day had a lower CCT. The rate of loss was reduced in those women using estrogen replacement therapy and increased in those women taking 3 grains or more of thyroid hormone. Women taking 3 grains or more of thyroid hormone should be advised that they are at higher risk for osteopenia.