Bidirectional association between GERD and rheumatoid arthritis: two longitudinal follow-up studies using a national sample cohort

Several previous studies have suggested a relationship between GERD and RA. However, no study has investigated the bidirectional relationship between GERD and RA. This study aimed to evaluate the causal relationships between rheumatoid arthritis (RA) and gastroesophageal reflux disease (GERD). Participants aged ≥ 20 years old in the Korean Health Insurance Review and Assessment Service-National Sample Cohort from 2002 to 2013 were enrolled. In study I, 132,140 GERD participants were 1:2 matched with 264,280 control I participants. In study II, 6615 RA participants were 1:4 matched with 26,460 control II participants. Both control I and control II groups were matched with their study groups for age, sex, income, and region of residence. The occurrence of RA (study I) and GERD (study II) were followed up in both the study and control groups. The hazard ratios (HRs) of GERD for RA (study I) and of RA for GERD (study II) were analysed using stratified Cox-proportional hazards models. In study I, 0.8% (1,034/132,140) of the GERD group and 0.5% (1,290/264,280) of the control I group had RA (P < 0.001). The GERD group demonstrated a 1.49-fold higher adjusted HR than did the control I group (95% confidence interval (95% CI) = 1.37-1.62, P < 0.001). In study II, 22.5% (1,490/6,615) of the RA group and 15.2% (4,034/26,460) of the control II group had GERD (P < 0.001). The RA group showed a 1.46-fold higher adjusted HR than did the control II group (95% CI = 1.38–1.55, P < 0.001). GERD and RA have bidirectional associations in Korean adult population.