Background: Subclinical hyperthyroidism is associated with low bone mineral density (BMD) and increased fracture risk. In healthy postmenopausal women, results regarding an association between thyroid-stimulating hormone (TSH) in the normal range and BMD are contradictory. Trabecular Bone Score (TBS), an index of bone micro- architecture, is often decreased in secondary osteoporosis (OP). The aim was to determine the association between thyroid hormones (TSH, fT4) and BMD, TBS, and the incident 5-year OP fractures, in euthyroid post- menopausal women.
Design and methods: We assessed 1475 women of the CoLaus/OsteoLaus cohort. We evaluated BMD at lumbar spine, femoral neck and total hip, lumbar spine TBS, and vertebral fracture with DXA. Incident major OP fractures were evaluated 5-year later by questionnaire and DXA. Women with anti-osteoporotic, antidiabetic, thyroid-modifying, hormone replacement or systemic corticoid treatment were excluded. Results: 533 women (age 68.4±7.3 years, BMI 25.9±4.6 kg/m2, TSH 2.03±0.87 mU/l, fT4 15.51±1.85 pmol/l) met the inclusion criteria. There was no significant association between TSH or fT4 and BMD measures at any site. A positive association was found between TSH and TBS (β=0.138, p<0.01), even after adjusting for age, BMI and duration of menopause (β=0.086, p<0.05). TBS was positively associated with fT4 on bivariate analysis only. After a 5-year follow-up, women with incident major OP fractures had lower TSH levels (1.77±0.13 vs. 2.05±0.04 mU/l, p<0.05) than women without fractures, while no difference was found for fT4.
Conclusion: In euthyroid postmenopausal women, TSH levels were positively associated with TBS and negatively with incident fractures, without affecting BMD. Further studies are needed to evaluate the influence of thyroid hormones on TBS.