Endocrine Abstracts

OPUS is a population-based prospective cohort study of post-menopausal women from five European cities. We investigated whether TSH, fT4 and fT3 are associated with fracture risk, bone mineral density (BMD) at hip and spine, bone formation (osteocalcin, procollagen type 1 N-terminal propeptide), bone resorption (N- and C-telopeptides of type 1 collagen, NTX, CTX), pulse rate, grip strength and balance. Vertebral fractures were determined at baseline and 6 years follow-up. Using strict exclusion criteria we defined a normal reference range for thyroid function tests (TFTs).

Results: In the whole population adjusted for age and body mass index (n=2374), higher fT4 levels were associated with higher levels of NTX (r=0.069, P<0.05) and CTX (r=0.066, P<0.05), and with lower BMD at hip (r=−0.089, P<0.05) and spine (r=−0.061, P<0.05). The associations with NTX (r=0.049, P<0.05) and spine BMD (r=−0.049, P<0.05) persisted after overt thyroid disease, sick euthyroid syndrome and medications affecting TFTs were excluded i.e. fT4 within the reference range (n=1754). Hierarchical multiple regression revealed fT4 was associated with spine BMD (β=−0.067, P=0.011). Higher TSH was inversely associated with NTX (r=−0.155, P<0.05) and CTX (r=−0.066, P<0.05) but TSH was not associated with BMD or incident fracture. Within the reference range, higher fT3 was associated with higher pulse rate (r=0.065, P<0.05; fT3 highest versus lowest quintile ANOVA F=4.438, P=0.025), better balance (r=0.099, P<0.005; F=4.262, P=0.03) and increased grip strength (r=0.195, P<0.005; F=11.572, P<0.0005). TSH was inversely associated with balance (r=−0.102, P<0.05) and grip strength (r=−0.080, P<0.05).

Conclusions: In post-menopausal women, the relationship between thyroid function and fracture risk is complex. Higher fT4 levels within the normal range are associated with reduced BMD. In contrast, low fT3 levels are associated with poorer balance and reduced muscle strength, both of which are potential risk factors for falls and fractures.