Quantified intakes of key diet components and the risk of developing rheumatoid arthritis: Results from a nested case-control study.

Objectives: This nested case-control study aimed to investigate the relationship between components of the Swedish food-based dietary guidelines (SDG) from 2015 and the risk of developing rheumatoid arthritis (RA).

Methods: Data were obtained from the prospective Malmö Diet and Cancer Study (MDCS) conducted 1991-1996. Diet was assessed at baseline using a validated diet history method. Incident RA cases until 2016 were identified through register linkage, followed by a validation process through review of medical records. For each case, 4 RA-free controls, matched for age, sex, and year of inclusion in the MDCS, were selected from the cohort. Adherence to the SDG was assessed using the SDG Score (SDGS) of 5 components. Multivariable logistic regression and restricted cubic splines (RCS) were applied to analyse the relationships among the SDGS, its components, and RA.

Results: A total of 305 incident RA cases (67% rheumatoid factor/anti-cyclic citrullinated peptide positive) were identified. Recommended intakes of vegetables and fruits (>400 g/day) and red and processed meat (<500 g/week) were associated with lower risks of RA, with multivariable-adjusted odds ratios of 0.64 (95% CI 0.43-0.94) and 0.60 (95% CI 0.38-0.97), respectively. RCS revealed a positive linear association for total intake of red/processed meat with RA development and a negative association for vegetables and fruits. The risk was higher by quartile of red and processed meat intake for seropositive, but not seronegative RA.

Conclusions: Higher intake of red/processed meat associated with a higher risk of seropositive RA, whereas vegetables and fruit may reduce the risk of RA overall.