Subclinical hyperthyroidism is associated with increased risk of vertebral fractures in older men

Summary: In elderly men included in MrOS-Sweden, subclinical hyperthyroidism (SHyper) was markedly associated with increased risk of vertebral fractures. Introduction: Overt hyperthyroidism is associated with increased risk of fractures. However, only a few studies have investigated whether SHyper is associated with fracture risk in elderly men. We therefore investigated if SHyper was a risk factor for fractures in Swedish men. Methods: We followed (median 9.8 years) elderly men (n = 1856; mean age 75, range 69–81 years) participating in the Gothenburg and Malmö subcohorts of the prospective, population-based MrOS-Sweden study. The statistical analyses included Cox proportional hazards regression. SHyper was defined as serum thyroid-stimulating hormone (TSH) < 0.45 mIU/L (n = 38). Results: SHyper was associated with increased risk of all fractures [n = 456; hazard ratio (HR) adjusted for age, study center, and levothyroxine treatment = 1.99, 95% confidence interval (CI): 1.20–3.32], major osteoporotic fractures (MOF, n = 338; HR 2.44, 95% CI: 1.42–4.21), and vertebral fractures (n = 176; HR 3.79, 95% CI: 2.02–7.11). These associations remained after full adjustment for covariates including total hip bone mineral density and in subanalyses including only men with serum free thyroxine ≤ the upper normal limit. However, after exclusion of men receiving levothyroxine treatment, the associations with all fractures and MOF lost significance. Conclusions: In elderly Swedish men, there was a strong association between SHyper and increased risk of vertebral fractures, whereas the associations with all incident fractures and MOF need to be confirmed in further studies.