Dietary fiber intake and rheumatoid arthritis among U.S. adults: Evidence from a cross-sectional analysis of NHANES with inflammatory markers as mediators.

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory disease in which diet may play a role. Dietary fiber has been suggested to reduce systemic inflammation, yet evidence on its relationship with RA remains limited. We examined whether dietary fiber intake is associated with RA prevalence and whether this association is mediated by inflammatory markers.

METHODS

We conducted a cross-sectional analysis of 15,114 U.S. adults aged ≥20 years from the National Health and Nutrition Examination Survey (NHANES, 2010-2020). Dietary fiber intake was assessed using two 24-h dietary recalls. RA status was based on self-reported physician diagnosis. Inflammatory status was evaluated using high-sensitivity C-reactive protein (Hs-CRP), the Dietary Inflammatory Index (DII), and the Systemic Immune-Inflammation Index (SII). Multivariable logistic regression models were used to estimate associations, with stratified analyses performed by sex. The models were comprehensively adjusted for covariates including demographics (age, race/ethnicity), socioeconomic status (education level, income), lifestyle factors (BMI, smoking, alcohol use), and comorbidities. Both parallel and serial mediation analyses were also applied to assess the role of inflammation.

RESULTS

The prevalence of RA in the study population was 6.97 %. Mean daily fiber intake was 16.9 g. Higher fiber intake was associated with a lower prevalence of RA (per 5 g/day increment: OR = 0.89, 95 % CI: 0.86-0.98). Fiber intake was inversely associated with Hs-CRP, DII, and SII, all of which were positively associated with RA. Mediation analyses indicated that inflammation explained part of the fiber-RA association, with proportions ranging from 10.65 % to 36.12 %; serial pathways through DII-Hs-CRP and DII-SII accounted for 7.45 % and 5.36 %, respectively.

CONCLUSIONS

In this nationally representative U.S. sample, higher dietary fiber intake was associated with lower RA prevalence, and this association was partially mediated by inflammatory indicators. These findings highlight the potential importance of dietary fiber in modulating inflammation and RA risk.