Longitudinal patterns of obesity index changes and risk of incident rheumatoid arthritis: evidence from a...

Obesity has been linked to increased rheumatoid arthritis (RA) risk, but the impact of longitudinal changes in obesity indices remains unclear. A clearer understanding of these dynamic patterns could enhance early identification and prevention strategies. This study aimed to examine the associations between longitudinal changes in body mass index (BMI), waist-to-hip ratio (WHR), and body roundness index (BRI) and the incidence of RA.

We analyzed data from 68,061 UK Biobank participants (aged 40-73 years) with at least two obesity index measurements. Obesity change patterns were categorized as stable or transitional, and the annual average rate of change (AARC) was calculated. Cox regression and restricted cubic spline (RCS) models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

Over a median follow-up of 4.06 years, 354 participants developed RA. Stable overweight (HR: 1.45; 95% CI: 1.12, 1.88), abdominal obesity (HR: 1.48; 95% CI: 1.12, 1.96) and high BRI (HR: 1.46; 95% CI: 1.12, 1.89) were related to an increased risk of RA. Additionally, the transition from non-abdominal obesity to abdominal obesity was connected to a 39% increase in RA risk (HR: 1.39; 95% CI: 1.00, 1.91). The RCS model showed a non-linear association between AARC in BMI and RA risk, with RA risk increasing when AARC exceeded 1.106 (P for non-linearity = 0.019).

The findings suggest that specific dynamic changes in obesity indices are associated with an increased risk of RA, and that maintaining a normal body composition may contribute to risk reduction.