Does Mediterranean Diet Provide Protection against Rheumatoid Arthritis?

The E3N study is a French prospective cohort including 98,995 women since 1990. Dietary data were collected through a food frequency questionnaire validated in 1993. Adherence to the Mediterranean diet was assessed using a 9-unit diet score that assesses consumption of vegetables, legumes, grain products, fish, meat, dairy products, olive oil, and alcohol. HRs and 95% CIs for rheumatoid arthritis events were estimated using Cox proportional-risk regression models adjusted for the main potential confounders, including age and smoking.

Among 62,629 women, 480 cases of rheumatoid arthritis were detected. In the entire population, the Mediterranean diet score was not associated with rheumatoid arthritis risk (HR: 0.86, 95% CI: 0.67 to 1.09 for high versus low score, Ptrend = 0.09); however, among smokers it was associated with a reduced risk of rheumatoid arthritis (HR: 0.91 for a 1-point increase in Mediterranean diet score; 95% CI: 0.84 to 0.99, P = 0.03). Smokers had an absolute risk of rheumatoid arthritis of 38.3 and 51.5/100,000 person-years with high and low Mediterranean diet scores, respectively, compared with never smokers (35.8/100,000 person-years).

In general, adherence to the MD was not associated with a decreased risk of RA, but it was associated with a decreased risk among women who smoked or used to smoke: Among those with high adherence to the Mediterranean diet, there were 383 cases of RA per 1 million per year, compared to 515 cases per 1 million among those with low adherence to the diet (358 cases per 1 million per year among women who never smoked and had high adherence to the diet.).

The results suggest that adhering to the Mediterranean diet may reduce the high risk of RA in smoker women. The results should be confirmed in future research.