Association between thyroid function and osteoarthritis: A population-based cohort study.

Objectives: Previous genetic and animal studies indicated a causal role of thyroid hormones in osteoarthritis (OA), which has not been observed in the general population. We aimed to investigate whether thyroid-stimulating hormone (TSH) and free thyroxine (FT4) were associated with hand, hip, or knee OA.

Methods: Participants from the Rotterdam Study with baseline TSH, FT4, and joint radiographs were included. We used multivariable regression models to investigate the association of thyroid function with the prevalence, severity, incidence, and progression of OA. We conducted stratified analyses by sex, age, body mass index (BMI) and weight-bearing physical activity.

Results: Among 9054 participants included (mean age 65 years, 56.3% women), higher FT4 concentrations were associated with an increased risk of prevalent knee OA (odd ratio [OR] 1.04 per pmol/L, 95% CI 1.01-1.06, corresponding to an OR of 1.62 across the reference range [i.e., 14pmol/L changes] of FT4) and more severe knee OA. There was a positive association between FT4 and overall progression of knee OA (OR 1.03 per pmol/L, 1.00-1.07). No association of TSH with hand, hip, or knee OA was identified. Stratified analysis revealed an association between FT4 and prevalent knee OA among individuals with BMI ≥30 kg/m² (OR 1.05 per pmol/L, 1.01-1.08) and those with high levels of weight-bearing physical activity (OR 1.05 per pmol/L, 1.01-1.10).

Conclusions: Our study indicated that higher FT4 concentrations may increase the risk of knee OA. This association might be greater in individuals with extra joint loading, such as those with obesity.