Influence of clinical characteristics and parameters associated with thyroid hormone therapy on the bone mineral density of women treated with thyroid hormone.

Reports of reduced bone mineral density (BMD) in patients receiving long-term replacement and suppression therapy with L-thyroxine have generated considerable interest and controversy. A substantial literature has evolved, with interpretation of conflicting results obscured by a variety of confounding factors. We examined the BMD measurements of 202 white women who were taking thyroid hormone to determine the contribution to BMD of a number of clinical characteristics and parameters associated with thyroid hormone therapy. Measurements of BMD (N = 335 over 2.6 +/- 1.6 years) of the spine (L2-L4) were performed in 195 subjects. The BMD of three sites of the hip was measured (N = 247 over 1.8 +/- 1.1 years) in 157 subjects. The BMD of the proximal radius was also measured (N = 172 over 1.8 +/- 1.2 years) in 124 subjects. Increasing age and a history of previous thyrotoxicosis had a deleterious effect on spine BMD. Body mass index (BMI) was positively correlated with spine BMD. Dose of thyroid hormone, duration of therapy, type of underlying thyroid disease, history of thyroidectomy, or serum-free thyroxine index did not influence either the initial BMD or the change in spine BMD over time. In the hip, age correlated with a decrease, and BMI with an increase in BMD. A history of previous thyrotoxicosis was associated with a decrease in hip BMD at all three sites (0.05 < p < 0.10). No other clinical parameters significantly influenced either the initial BMD or the change in hip BMD over time. Increasing age and dose of thyroid hormone, and a prior history of thyrotoxicosis had a deleterious effect on the BMD at the proximal radius. In summary, thyroid hormone therapy was not associated with a significant effect on BMD of the spine or hip, but a decreased BMD of the proximal radius was related to both previous thyrotoxicosis and to dose of thyroid hormone.