High sodium intake is associated with self-reported rheumatoid arthritis: a cross sectional and case control analysis within the SUN cohort

Sodium intake is a potential environmental factor for immune-mediated inflammatory diseases. The aim of this study is to investigate the association of sodium intake with rheumatoid arthritis. We performed a cross-sectional study nested in a highly educated cohort investigating dietary habits as determinants of disease. Daily sodium intake in grams per day was estimated from a validated food frequency questionnaire. We identified prevalent self-reported cases of rheumatoid arthritis. Logistic regressionmodelswere used to estimate the odds ratio for rheumatoid arthritis by sodium intake adjusting for confounders. Linear trend tests and interactions between variables were explored. Sensitivity analyses included age- and sex-matched case–control study, logistic multivariate model adjusted by residuals, and analysis excluding individuals with prevalent diabetes or cardiovascular disease. The effective sample size was 18,555 individuals (mean age 38-years old, 60% women) including 392 self-reported rheumatoid arthritis. Median daily sodium intake (estimated from foods plus added salt) was 3.47 (P25–75: 2.63–4.55) grams. Total sodium intake in the fourth quartile showed a significant association with rheumatoid arthritis (fully adjusted odds ratio 1.5; 95% CI 1.1–2.1, P for trend¼0.02). Never smokers with high sodium intake had higher association than ever smokers with high sodium intake (P for interaction¼0.007). Dosedependent association was replicated in the case–control study. High sodiumintakemay be associated with a diagnosis of rheumatoid arthritis. This confirms previous clinical and experimental research