l-Thyroxine prevents the bone-conserving effect of HRT in postmenopausal women with subclinical hypothyroidism

• Published in: Gynecological endocrinology 1999, Vol.13 (3), p.196-201
• Main Authors: Pines, A., Dotan, I., Tabori, U., Villa, Y., Mijatovic, V., Levo, Y., Ayalon, D.
• Format: Article
• Language: English
• Subjects: Adult; Bone Density - drug effects; Bone Mineral Density; Female; Hormone Replacement Therapy; HRT; Humans; Hypothyroidism - drug therapy; L-Thyroxine; Medical Records; Middle Aged; Postmenopause; Retrospective Studies; Subclinical Hypothyroidism; Thyroxine - pharmacology; Thyroxine - therapeutic use
• ISSN: 0951-3590; 1473-0766
• DOI: 10.3109/09513599909167555

Hypothyroidism, which is a common disorder among postmenopausal women, may be associated with higher than average bone mineral content. Contrarily, treatment with L-thyroxine may cause a significant bone loss. The aim of our study was to evaluate the effects of hormone-replacement therapy (HRT) on bone density in women with subclinical hypothyroidism treated with L-thyroxine. A total of 73 postmenopausal women with thyroid-stimulating hormone (TSH) levels > 5 mU/l and normal free thyroxine values, who never used HRT or L-thyroxine, were divided into three groups according to the treatment given during a 3-year follow-up period: 34 women received only HRT; 20 women received HRT and L-thyroxine, and the remaining 19 women received neither medications. A euthyroid control group included 41 postmenopausal women with TSH levels between 0.5 and 1.5 mU/l, who were using HRT since the initial visit. Lumbar spine bone density measurements were performed at baseline and study termination. Taken as a whole, the hypothyroid women had a non-significant higher baseline bone mineral density (BMD) as compared to the euthyroid controls (1.068 0.19 g/cm2 vs. 1.024 0.15). After 3 years, both the euthyroid and hypothyroid women on HRT only had an increase in BMD (0.032 0.04 g/cm2 and 0.028 0.05 g/cm2, respectively; p < 0.001 for both, compared to baseline). Hypothyroid women using no medication had a decrease of 0.034 0.07 g/cm2 in BMD, and those receiving both HRT and L-thyroxine lost the most: 0.04 0.08 g/cm2 (p < 0.05 for both, compared to baseline). The addition of L-thyroxine thus prevented the beneficial effect of HRT on BMD. Thyroid hormone replacement is recommended only when overt symptoms of hormone deficiency occur. In such cases, a single bone-conserving treatment with HRT may not suffice.