Background The dietary inflammatory index (DII®), a quantitative measure of the inflammatory potential of daily food and nutrient intake, and associations between a variety of health outcomes have been reported. However, to the best of our knowledge, there is no report which investigated the association between rheumatoid arthritis (RA) and DII. Therefore, we investigate the association between the DII and disease activity in patients with RA.
Methods We performed a cross-sectional and longitudinal analysis using 6 years of data (from 2011 to 2017) in TOMORROW, a 10-year prospective cohort study consisting of 208 RA patients and 205 gender- and age-matched non-RA controls recruited in 2010. Disease activity of RA patients was assessed annually using DAS28-ESR (disease activity score 28 joints and the erythrocyte sedimentation rate) as a composite measure based on arthritic symptoms in 28 joints plus global health assessment and ESR. Dietary data were collected in 2011 and 2017 using the brief-type self-administered diet history questionnaire (BDHQ). Energy-adjusted DII (E-DIITM) score was calculated using 26 nutrients derived from the BDHQ. Data were analyzed with two-group comparisons, correlation analysis, and multivariable logistic regression analysis.
Results RA patients had significantly higher E-DII (pro-inflammatory) score compared to controls both in 2011 and 2017 (p < 0.05). E-DII score showed statistically significant negative correlation with age in RA patients, both in 2011 (r = -0.20) and 2017 (r = -0.23). Controls also showed a similar trend. In RA patients, E-DII score was not a factor associated with disease activity in a cross-sectional analysis. However, decline in E-DII (anti-inflammatory change) score was a factor that increased the odds of maintaining low disease activity (DAS28-ESR ≤ 3.2) or less for 6 years (OR: 4.33, 95%CI: 1.66-11.29, p = 0.003).
Conclusions E-DII score was high in RA patients and lowering E-DII score over time may be beneficial in controlling disease activity in patients with RA.
Trial registration UMIN Clinical Trials Registry, http://www.umin.ac.jp/ctr/, UMIN000003876. Registered 7 Aug 2010 - Retrospectively registered.