A systematic review and meta-analysis of observational studies on the association between animal protein sources and risk of rheumatoid arthritis

Summary Objective The aim of this study was to investigate the linear and nonlinear dose–response associations of animal-based dietary protein intake and risk of developing rheumatoid arthritis (RA). Methods A systematic search of MEDLINE, Scopus and Embase was conducted up to October 2020. Observational studies that report risk estimates of RA for animal-based protein consumption were included. We calculated pooled relative risks (RRs) by using a random-effects model. Linear and non-linear dose–response analyses were performed to examine the dose–response relations between animal-based protein consumption and RA. Results Seven cohort studies (n = 457,554) with 3545 incident cases and six case–control studies with 3994 cases and 5252 controls were identified. Highest compared with the lowest category of fish consumption was inversely associated with risk of RA (RR: 0.89; 95% CI, 0.80 to 0.99; I2 = 0%, n = 10). Also, a 100 g/day increment in fish intake was associated with a 15% decreased risk of RA. Dose–response analysis showed a modest U-shaped association between fish consumption and incidence of RA, with the lowest risk at a fish intake of 20–30 g/day (Pnon-linearity = 0.04). We found no significant association between consumption of red meat, poultry or dairy and the risk of RA. Conclusion The present study revealed a significant reverse association between fish consumption and risk of RA. While we observed no association between red meat, dairy or poultry consumption and risk of RA. Further well-designed prospective studies are needed to support our findings.