Mediterranean diet and incidence of rheumatoid arthritis in women.

OBJECTIVE:
We examined the association between a Mediterranean dietary pattern, as measured by the Alternate Mediterranean Diet Score (aMed), and risk of incident rheumatoid arthritis (RA) in US women.

METHODS:
We prospectively followed 83,245 participants from the Nurses' Health Study (NHS; 1980-2008) and 91,393 participants from NHS II (1991-2009) who were initially free of baseline connective tissue diseases. Dietary information was obtained via validated food frequency questionnaires at baseline and approximately every 4 years during followup. The aMed score was calculated according to the consumption status of 9 food components using cumulative average value. Time-varying Cox proportional hazards models were used to calculate hazard ratios (HRs) for RA, seropositive RA, and seronegative RA after adjustment for potential confounding factors. Results from 2 cohorts were pooled by an inverse variance-weighted, fixed-effects model.

RESULTS:
During 3,511,050 person-years of followup, 913 incident cases of RA were documented in the 2 cohorts. After adjustment for several lifestyle and dietary variables, in both cohorts greater adherence to Mediterranean dietary pattern was not significantly associated with altered risk of RA. The pooled HR for women in the highest quartile of the aMed score was 0.98 (95% confidence interval 0.80-1.20) compared with those in the bottom quartile. Similar nonsignificant results were observed for both seropositive and seronegative RA. We did not find significant associations between each individual food component (except for alcohol) of the aMed score and risk of incident RA.

CONCLUSION:
We did not find a significant association between a Mediterranean dietary pattern and the risk of RA in women.