Background/Purpose: Omega-3 fatty acids downregulate pro-inflammatory cytokines, thus have been of interest as adjunctive rheumatoid arthritis (RA) therapy for decades. We previously reported an inverse association between disease activity measured by DAS28-CRP and frequency of fish consumption in an RA cohort.¹ The present study tested whether individual components of DAS28-CRP or other inflammatory cytokines were related to frequency of fish intake.

Methods:  We conducted a cross-sectional analysis using baseline data from participants in a prospective cohort study of cardiovascular disease in RA. Frequency of fish consumption was assessed by a baseline food frequency questionnaire assessing usual diet in the past year. DAS28-CRP was calculated using tender joint count (TJC), swollen joint count (SJC), and C-reactive protein (CRP) measured at baseline. Multivariable, total energy-adjusted linear regression models provided effect estimates and 95% confidence intervals (CI) for frequency of non-fried fish consumption (never to <1/month, 1/month to <1/week, 1/week, and ≥2/week) on baseline TJC, SJC, and natural log (ln)-transformed cytokine levels. We also estimated the difference in each outcome associated with increasing fish consumption by one serving per week. A sensitivity analysis additionally adjusted for pack-years.

Results:  Among 176 participants, 60% were female and median age was 59 years (interquartile range [IQR] 53-65). Seventy-nine percent were seropositive (RF or anti-CCP), median disease duration was 9 years (IQR 5-17), and median DAS28-CRP was 3.5 (IQR 2.9-4.3). Current medications taken as mono- or combination therapy included non-biologic disease modifying anti-rheumatic drugs (DMARDs) in 87%, biologic DMARDs in 46%, glucocorticoids in 39%, and fish oil supplements in 9%. Twenty percent ate fish never to <1/month and 18% ate fish ≥2 times/week. In adjusted linear regression models, subjects consuming fish ≥2 times/week had a significantly lower SJC compared with subjects who ate fish never to <1/month (difference -3.51 [95% CI -5.87, -1.16]) (Table). For each additional serving of fish per week, SJC was significantly reduced by 1.18 (95% CI -2.03, -0.33). We did not observe differences in TJC or ln-transformed cytokine levels based on frequency of fish consumption. Further adjustment for smoking produced similar results.

Conclusion: Differences in SJC according to frequency of fish consumption may explain our previous observation that higher intake of fish was associated with lower disease activity as measured by DAS28-CRP in RA patients.

1. Tedeschi SK, Bathon JM, Giles JT, Lin T-C, Yoshida K, Solomon DH. The relationship between fish consumption and disease activity in rheumatoid arthritis. Arthritis Care Res. 2017 [in press]