Consuming a Mediterranean diet did not reduce the risk of developing rheumatoid arthritis (RA), but did limit the risk among those who ever smoked, a large French study found.
Adherence to the Mediterranean diet was not associated with a lower risk of RA in more than 60,000 women enrolled in a prospective study evaluating environmental factors and chronic disease, with a risk of 0.86 (95% CI 0.67–1.10). P= 0.11), said Marie-Christine Boutron-Ruault and colleagues, MD, PhD, of the Université Paris-Sud in Villeju.
However, for those who had ever smoked, higher adherence to the Mediterranean diet reduced the risk, with a risk of 0.91 (95% CI 0.84–0.99). P= 0.03), the researchers pointed out Arthritis and rheumatism.
RAA is thought to result from an interaction of genetic and environmental factors, with smoking being the only environmental factor that is clearly associated with the disease. It appears to be less common in southern European countries than with its northern neighbors.
Dietary factors have been suggested as contributing, but previous studies have mainly focused on single foods or nutrients, and patterns of food consumption may provide a more realistic assessment.
Common Mediterranean diets throughout southern Europe mainly include grains, fruits and vegetables, olive oil, and fish, with only moderate amounts of meat, dairy and wine. Its use has been associated with a lower risk of cardiovascular and neoplastic diseases, but because it also contains antioxidants and n-3 fatty acids, it may also affect the risk of autoimmune diseases such as RA.
To explore this, Boutron-Ruault and colleagues analyzed data from the E3N-EPIC prospective cohort study of healthy women in France. Most were born during 1925 to 1950, and enlisted in 1990. They responded to biennial questionnaires regarding health and lifestyle concerns, as well as diagnosing the disease including RA. A dietary questionnaire was sent from 1993 to 1995 along with the third primary questionnaire. More than 200 specialty foods were included.
A Mediterranean diet score of 0–9 was calculated, giving positive scores according to zeros given for potentially beneficial foods such as vegetables, grains, and olive oil, and non-Mediterranean items such as dairy and meat. Scores were then classified as following a low (score of 0–3), moderate (4–5), or high (6–9) diet. Daily amounts of individual food groups were also classified as reference, medium, or high. For example, grain consumption was considered to be below 120 g / day in reference, moderate to 157 to 278 g / day and, if more than 278 g / day.
There were 480 incident cases of RA among the 62,639 women involved. The average age at the time of the dietary questionnaire was 52.5 years, and the average age of RA diagnosis was 65.2 years.
Most of the participants were teachers or other professionals and at least some had university schooling. Current smoking was reported by 13.2% and prior smoking by 33.2%. Total daily calorie intake was 2,136.3 kcal. Mediterranean diet scores were low in 29.2%, moderate 45.2%, and high in 25.5%.
The only food group associated with lower risk of RA was fish, where moderate consumption of 9 to 25 g / day had a lower risk compared with consumption lower than the reference volume of 9 g / day (HR 0.74, 95%). CI 0.59–0.94). No difference in risk was observed for high consumption of any food group.
In addition, there was no difference in risk for smokers (HR 0.99, 95% CI 0.91–1.07, compared with never-smokers at risk reduction with high-Mediterranean diet scores) P= 0.74).
Finally, the risks of RA were highest among smokers with low Mediterranean diet scores (HR 1.44, 95% CI 1.03–2–13). The rate of RA among ever-smokers with a low diet score was 51.5 per 100,000 person-years, while the rate decreased to 38.3 per 100,000 person-years for never-smokers with a high diet score. The rate was close for those. With a high diet score, at 35.8 per 100,000.
Because risk-differences may sometimes exist between smokers, researchers suggested that the pathophysiological process may vary between groups, with smoking implicated in pulmonary citrullination.
“They have written that the antioxidant effects of the Mediterranean diet may increase the oxidant effects of smoking. Thus, strong adherence to the Mediterranean diet may reduce the increased risk of RA associated with smoking,” he wrote.
Limitations of the study included only French women and the researchers’ inability to adjust smoking duration and intensity. He called for further study to confirm his findings.
The authors stated no financial disturbances of interest.