Mediterranean diet and risk of rheumatoid arthritis: a population-based case-control study

Background: The Mediterranean diet has been associated with lower mortality and lower risk of cardiovascular diseases and cancer. Although its components have been analysed in several studies, only one study has specifically investigated the association between Mediterranean diet and risk of rheumatoid arthritis (RA), and reported no association. Methods: Data on 1721 patients with incident RA (cases) and 3667 controls, matched on age, gender and residential area, from the Swedish epidemiological investigation of RA (EIRA), a population-based case-control study, were analysed using conditional logistic regression. The Mediterranean diet score, ranging from 0 to 9, was calculated from a 124-item food frequency questionnaire. Results: In the EIRA study (median age of participants 53 years), 24.1% of the patients and 28.2% of the controls had high adherence to the Mediterranean diet (a score between 6 and 9). After adjustments for body mass index, educational level, physical activity, use of dietary supplements, energy intake, and smoking, high adherence reduced the odds of developing RA by 21% (OR 0.79; 95% CI 0.65-0.96) as compared to low adherence (a score between 0 and 2). The OR was even lower among men (OR 0.49; 95% CI 0.33-0.73), but no significant association was found among women (OR 0.94; 95% CI 0.74-1.18). An association between high diet score and low risk of RA was observed in rheumatoid factor (RF)-positive (OR 0.69; 95% CI 0.54-0.88), but not RF-negative RA (OR 0.96; 95% CI 0.681.34), and in RA characterised by presence of antibodies to citrullinated peptides (ACPA), but not in ACPA-negative RA. Conclusions: In this large population-based case-control study, the Mediterranean diet score was inversely associated with risk of RA However, an association was only found among men and only in seropositive RA.