8/14/13

A diet rich in fatty fish appeared to protect against rheumatoid arthritis (RA) in women, results of a large cohort study showed.

Regular consumption of a diet rich in omega-3 fatty acids was associated with 35% lower odds of RA over the short term, increasing to more than a 50% risk reduction with long-term intake of the fatty acids, found in abundance in salmon and other fatty fish.

Consuming at least one serving of any fish weekly reduced the risk of RA by almost 30%, although the impact did not reach statistical significance, Alicja Wolk, DrMedSci, of the Karolinska Institute in Stockholm, and co-authors reported online in Annals of Rheumatic Diseases.

“The study indicates a potentially important role for dietary long-chain n-3 polyunsaturated fatty acids (PUFAs) in the etiology of RA, and that adherence to existing dietary guidelines regarding fish consumption may also be beneficial in terms of RA risk,” the authors concluded.

The findings add to those from another Swedish study showing a 20% reduction in RA risk among men and women who reported eating at least one serving of fatty fish per month.

Fish oil supplementation is the only source of long-chain n-3 PUFAs consistently associated with a reduced risk of RA. Studies of dietary sources of n-3 PUFAs have yielded inconsistent results, Wolk and colleagues noted.

Continuing the exploration of n-3 PUFAs and RA risk, investigators examined the association of recent and long-term dietary intake of long-chain n-3 PUFAs and RA in a large prospective cohort of middle-age and older women. The study population was drawn from the Swedish Mammography Cohort, which involved women born from 1914 to 1948 and living in two Swedish counties during two survey periods, one in 1987 and one in 1997.

The first survey elicited information regarding diet, height, weight, parity, and education. The second survey expanded the questioning to include smoking history, physical activity, and use of dietary supplements and aspirin.

The final analysis included 32,232 women, 205 of whom developed RA during a mean follow-up of 7.5 years. Stratifying the participants into quintiles of dietary long-chain n-3 PUFAs yielded intake groups ranging from ≤0.21 to >0.49 g/day. The lowest intake quintile included the highest proportion of smokers (24%) and the lowest proportion of alcohol drinkers (72.9%) and aspirin users (41.1%).

Of the 205 women who developed RA, 27% had daily n-3 intake ≤0.21 g/day compared with 20% for the entire cohort.

Comparison of the lowest and second quintile of dietary long-chain n-3 PUFAs showed a 39% reduction in the relative risk of RA among women in the second quintile (RR 0.61, 95% CI 0.40-0.93).

After adjustment for smoking, alcohol intake, aspirin use, and total energy intake, women in the highest n-3 PUFA intake quintile had a 33% lower relative risk of RA compared with women in the lowest quintile. However, the confidence intervals overlapped the point of unity (RR 0.67, 95% CI 0.44-1.03). Further adjustment for education, body mass index, physical activity, and individual PUFAs still yielded a relative risk of 0.67, which remained nonsignificant (95% CI 0.40-1.11).

Comparing the lowest quintile and the remaining quintiles combined yielded a 35% reduction in the risk of RA for higher intake of n-3 PUFAs. The data showed a population-prevented fraction of 0.28, meaning that 28% of the hypothetical total disease burden could be prevented by consuming >0.21 g/day of dietary long-chain n-3 PUFAs.

Analysis of women who completed both surveys (long-term dietary intake) showed that consistent intake >0.21 g/day of dietary long-chain n-3 PUFAs was associated with a statistically significant 52% reduction in the risk of RA as compared with women who reported lower intake on both surveys (95% CI 29% to 67%).

Analysis of long-term fish consumption (irrespective of fatty acid concentration) yielded a relative risk of 0.71 for RA among women who reported consuming at least one serving of fish per week on both surveys (95% CI 0.48-1.04).

• Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

last updated 08.15.2013