Mediterranean Diet May Prevent RA in Current or Previous Smokers

The Mediterranean diet (MD), which is rich in olive oil, cereals, fruit and vegetables, fish, and a moderate amount of dairy, meat, and wine, may help prevent rheumatoid arthritis (RA) in current or previous smokers, according to new research published in Arthritis & Rheumatology.

French researchers analyzed 62,629 French women who had been taking part in the E3N Study, a questionnaire-based study assessing dietary intake since 1990.

RA is known to affect women more than men and the prevalence appears to be higher in Northern European countries compared with Southern European countries. Previous research has also shown that smoking is a risk factor for anti-citrullinated protein antibody–positive RA.

“Environmental and lifestyle factors, including dietary habits, might partly explain this difference,” the authors explained. They noted that the MD is widespread in Southern European countries. Previous research has shown the benefits of the MD on overall mortality and cardiovascular diseases.

Traditionally, the MD score includes 9 components with 7—legumes, vegetables, fruits and nuts, cereal products, fish, olive oil, and moderate alcohol consumption—positively associated with the score and 2—meat and dairy products—negatively associated. A variant of the score replaces olive oil consumption, which is minimal in non-Mediterranean populations, with the ratio of unsaturated to saturated fatty acids.

People are assigned a 1 or 0 based on their consumption of each of the components of the MD. Consumption of a beneficial component that is below the median consumption is assigned a 0; consumption of that component above the median is assigned a 1. Similarly, consumption of the detrimental components that is below the median is assigned a 1. In total, the MD score ranges from 0 to 9 to reflect low (0-3), medium (4-5), or high (6-9) adherence to the MD.

In the overall study population, 29.2% of women had a low MD score, 45.2% had a medium score, and 25.5% had a high score.

Among the 62,639 women who were included in the study, there were 480 incident RA cases. The mean age at diagnosis of RA was 65.2 years. The only food group associated with the risk of RA was fish: a medium consumption of fish, on average 9 to 25 grams per day, was associated with a decreased risk of RA. There was no association with high consumption, or more than 25 grams per day. Otherwise, no food group was individually associated with the risk of RA.

The researchers found that, 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 ever-smokers, we found an inverse association between MD score and the risk of RA, a higher MD score being associated with a decreased risk of RA,” the authors wrote, and they added that “There was no association among never-smokers.”

The absolute risk of RA was lowest in never smokers with a high MD score (35.8/100,000 person-years) and highest in ever smokers (51.5/100,000 person-years). The authors noted that having a high MD score reduced the risk associated with smoke, though, bringing the absolute risk (38.3/100,000 person-years) close to the risk in never smokers with a similar diet.

Some of the limitations the authors noted included the fact that they were only studying French women and that the dietary habits were only assessed one time. They added that they were not able to take into account the intensity and duration of smoking.

“In conclusion, MD could reduce the excess risk of RA in ever smoker women,” the authors wrote. “Our findings must be confirmed in other prospective cohorts.”

Reference

Nguyen Y, Salliot C, Gelot A, et al. Mediterranean diet and risk of rheumatoid arthritis: findings from the French E3N‐EPIC cohort study. Arthritis Rheum. Published online September 9, 2020. doi:10.1002/art.41487