Background Dietary intake of omega-3 fatty acids (FA) may play a role in etiology of RA [1] and has also been shown to be anti-inflammatory in RA [2]. Increased intake of omega-6 FA as well as omega-6:3 FA ratio are associated with inflammation in RA [3]. However, little is known about how omega-3 FA may affect pain in RA.

Objectives To study the association between omega-3, omega-6, omega-6:3 FA ratio and pain, despite inflammatory control, after three months of MTX treatment in early RA patients.

Methods We included newly diagnosed RA patients with MTX monotherapy from Epidemiological Investigation of Rheumatoid Arthritis (EIRA) study linked to clinical data from Swedish Rheumatology Quality register (SRQ). Data on omega-3, omega-6, and omega-6:3 FA ratio (dietary questionnaires) were linked with data on self-assessed pain after three months of MTX treatment. Pain despite inflammatory control (Remaining Pain) was defined based on the Patient Acceptance Symptom Scale (PASS)[4] together with low systemic inflammation (VAS pain >40mm and CRP<10mg/L). Statistical analysis: logistic regression adjusted for age, sex, smoking, education, BMI, energy intake and omega-3 FA supplementation.

Results We included 591 patients (median age: 55 years; females: 70.6%; ACPA+: 67.9%). Mean values for clinical measures at baseline were: DAS28 5.2±1.3, VAS pain 53.9±24.7 and HAQ 1.1±0.6. Mean BMI was 25.8±4.7 kg/m². Omega-3 FA supplements were used by 19.5% of the patients. After three months, 92 patients (15.6%) had Remaining Pain. These patients had lower intake of omega-3 FA compared to those without Remaining Pain (0.6±0.4 vs. 0.7±0.3 g/day, p=0.004). Omega-3 FA intake was inversely associated with Remaining Pain (OR=0.5 [95% CI 0.3–0.9]), after adjustment. Omega-6:3 FA ratio but not omega-6 FA alone was directly associated with remaining pain (OR=2.3 [95% CI 1.3–4.2]). Similar ORs were found after adjustment for ACPA and physical activity. Omega-3 FA was not associated with CRP or EULAR response at the follow-up.

Conclusions Omega-3 FA was inversely associated with Remaining Pain and omega-6:3 FA ratio was directly associated with Remaining Pain. These associations were independent of inflammation. Our data suggest that dietary omega-3 FA may dampen the development of chronic pain in early RA.

1. Di Giuseppe, D., et al., Long-term intake of dietary long-chain n-3 polyunsaturated fatty acids and risk of rheumatoid arthritis: a prospective cohort study of women. Ann Rheum Dis, 2014. 73(11): p. 1949–53.

2. Ariza-Ariza, R., M. Mestanza-Peralta, and M.H. Cardiel, Omega-3 fatty acids in rheumatoid arthritis: an overview. Semin Arthritis Rheum, 1998. 27(6): p. 366–70.

3. Sundrarjun, T., et al., Effects of n-3 fatty acids on serum interleukin-6, tumour necrosis factor-alpha and soluble tumour necrosis factor receptor p55 in active rheumatoid arthritis. Journal of International Medical Research, 2004. 32(5): p. 443–454.

4. Pham, T. and F. Tubach, Patient acceptable symptomatic state (PASS). Joint Bone Spine, 2009. 76(4): p. 321–3.

Disclosure of Interest None declared