Consistent dietary intake of long-chain n-3 polyunsaturated fatty acids typically found in fish was associated with a reduced risk of rheumatoid arthritis in a prospective cohort study of Swedish women.
The study of 32,232 middle-aged and older Swedish women included 205 who developed rheumatoid arthritis (RA) during a mean follow-up of 7.5 years. Those who reported intake of more than 0.21 g/day of dietary long-chain n-3 polyunsaturated fatty acids (PUFAs), also called omega-3 fatty acids, at the time of an assessment in 1997 had a 35% reduction in the risk of developing RA, compared with women who reported lower intake (adjusted relative risk, 0.65), reported Dr. Daniela Di Giuseppe of the Karolinska Institute, Stockholm, and her colleagues.
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A new study found that consumption of long-chain n-3 polyunsaturated fatty acids typically found in fish was associated with a reduced risk of rheumatoid arthritis.
"The population prevented fraction, the equivalent of the population attributable risk when analyzing a protective factor, was 0.28. This indicates that 28% of the hypothetical total load of disease could be prevented by exposure to greater than 0.21 g/day of dietary long-chain n-3 PUFAs," the investigators wrote.
Consistent long-term intake of more than 0.21 g/day was associated with even greater risk reduction. Women who reported intake at that level at assessments in both 1987 and 1997 had a 52% reduction in risk, compared with those with lower intake (adjusted RR, 0.48), they said.
Those who reported consistent long-term consumption of at least one serving of fish weekly had a 29% reduction in risk, compared with those who had less than one serving weekly (adjusted RR, 0.71), they noted (Ann. Rheum. Dis. 2013 Aug. 12 [doi: 10.1136/annrheumdis-2013-203338]).
"The inverse association between fish consumption and RA can be attributed mainly to its content of long-chain n-3 PUFAs," they wrote.
Of note, the use of fish oil supplementation was not associated with the development of RA in this study (relative risk, 1.32 for ever vs. never users). However, there were only 17 users, and information about dose and duration of use was lacking.
Study subjects were participants in the population-based Swedish Mammography Cohort. The women, who were aged 54-89 years at follow-up, completed detailed food-frequency questionnaires at the 1987 and 1997 assessments.
The multivariable relative risks for dietary long-chain n-3 PUFAs were adjusted for cigarette smoking, alcohol intake, aspirin use, and energy intake. The multivariable relative risks for long-term fish consumption were also adjusted for quartiles of red meat and dairy food consumption.
The findings have implications for dietary guidelines with respect to fish consumption, the investigators said.
RA is known to be influenced by both genetic and environmental factors, but little is known about important modifiable risk factors other than smoking and alcohol consumption, they said, noting that the evidence regarding a role for dietary long-chain n-3 PUFAs has been limited, and study results have been conflicting.
However, the current study suggests that intake of at least 0.21 g/day is indeed of benefit. That intake is about the equivalent of at least one serving of fatty fish, such as salmon, or four servings of lean fish, such as cod, each week, the investigators explained. They suggested that dietary long-chain n-3 PUFAs may protect against RA through their anti-inflammatory properties, particularly through the synthesis of eicosanoids.
These intake levels are in line with recommendations from the American Dietary Guideline Advisory Committee, which advised eating fish twice weekly.
"In conclusion, the study indicates a potentially important role for dietary long-chain n-3 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," they wrote.
The study was supported by research grants from the Swedish Research Council/Committee for Research Infrastructure for Maintenance of the Swedish Mammography Cohort, and from the Karolinska Institute’s Award for Ph.D. Students. The authors reported having no disclosures.