Lower TSH, higher FT4 up risk of hip fracture in euthyroid adults
Lower thyroid-stimulation hormone (TSH) and higher free thyroxine (FT4) may increase the risk of hip fracture in euthyroid individuals, suggests a recent study.
Researchers conducted an individual participant data analysis on 13 prospective cohort studies with baseline examinations between 1981 and 2002 to assess the association of TSH and FT4 with incident fractures in euthyroid individuals. The participants were adults with baseline TSH of 0.45 to 4.49 mIU/L.
Hip fracture was the primary outcome, and secondary outcomes were any, nonvertebral and vertebral fractures. For clinical relevance, researchers analysed TSH according to five categories: 0.45 to 0.99 mIU/L; 1.00 to 1.49 mIU/L; 1.50 to 2.49 mIU/L; 2.50 to 3.49 mIU/L; and 3.50 to 4.49 mIU/L (reference). FT4 was assessed as study-specific standard deviation increase, because assays varied between cohorts.
Overall, 2,565 (4.5 percent) out of 56,835 participants had hip fracture (12 studies with data on hip fracture) during 659,059 person-years. For hip fracture, the pooled adjusted hazard ratio (HR) was 1.25 (95 percent CI, 1.05 to 1.49) for TSH 0.45 to 0.99 mIU/L, 1.19 (1.01 to 1.41) for TSH 1.00 to 1.49 mIU/L, 1.09 (0.93 to 1.28) for TSH 1.50 to 2.49 mIU/L and 1.12 (0.94 to 1.33) for TSH 2.50 to 3.49 mIU/L (p=0.004 for trend).
In addition, hip fracture correlated with FT4 (HR, 1.22; 1.11 to 1.35 per one standard deviation increase in FT4). Only FT4 was associated with any and nonvertebral fractures. In sensitivity analyses, the findings remained similar.
These results may help improve the definition of optimal ranges of thyroid function tests, according to researchers.