Mendelian randomization study on the causal effects of omega-3 fatty acids on rheumatoid arthritis.

Objectives: To resolve the ongoing debate on the role of plasma omega-3 fatty acids in rheumatoid arthritis (RA), we attempted to identify the association between omega-3 intake and the risk of RA.

Methods: We analyzed data from the largest genome-wide association study (GWAS) for omega-3 fatty acids (N = 114,999 of European ancestry) and RA (14,361 cases and 43,923 controls of European ancestry). Mendelian randomization-egger_intercept, MR-PRESSO, and Cochran's Q test were used to determine pleiotropy and heterogeneity. Egger, weighted median, inverse variance weighted (IVW), simple mode, and weighted mode were used to evaluate the causal association of plasma omega-3 levels on RA.

Results: We found no significant pleiotropy, heterogeneity, and bias among the omega-3 genetic instrumental variables (IVs) in RA GWAS datasets. MR analysis demonstrated that as omega-3 levels genetically increased, the risk of MS increased using MR-egger (Beta = 0.137, p = 0.037; OR = 1.146, 95% CI: [1.014, 1.296]), weighted median (Beta = 0.162, p = 0.001; OR = 1.176, 95% CI: [1.070, 1.292]), IVW (Beta = 0.102, p = 0.025; OR = 1.108, 95% CI: [1.013, 1.211]), simple mode (Beta = 0.219, p = 0.149; OR = 1.245, 95% CI: [0.931, 1.665]), and weighted mode (Beta = 0.146, p = 0.006; OR = 1.157, 95% CI: [1.051, 1.274]).

Conclusions: Our analysis suggested a causal association between genetically increased plasma omega-3 levels and the increased risk of RA in populations with European ancestry. Thus, to reduce the risk of RA, those of European descent should reduce omega-3 intake. Key Points • No significant pleiotropy or heterogeneity among the omega-3 genetic IVs in RA GWAS datasets. • Genetically increased plasma omega-3 levels enhanced the risk of RA in European lineages.