A study published online today in the Annals of the Rheumatic Diseases indicates that a regular weekly portion of fatty fish, such as salmon, or four servings of lean fish, such as cod, can halve the risk of developing rheumatoid arthritis.
The benefits of a fishy diet, which needs to be kept up for at least a decade, are largely attributable to its long chain omega 3 polyunsaturated fatty acid (PUFA) content, confirm the researchers.
They collected information on the dietary habits of more than 32,000 women born between 1914 and 1948, whose health was tracked between 2003 and 2010 as part of the Swedish Mammography Cohort population based study.
The researchers were particularly keen to assess dietary intake of omega 3 PUFAs as previous evidence shows that they have anti-inflammatory properties.
The women, all of whom lived in two counties of Sweden, completed a questionnaire on dietary intake, height, weight, motherhood and educational attainment between 1987 and 1990.
In 1997, the 56,000 who were still alive were sent a similar questionnaire, requesting further information on smoking, exercise, use of dietary supplements and aspirin.
As part of the dietary information requested, the women completed food frequency questionnaires, in which they detailed how often and how much they ate any of 67 (1987) and 96 (1997) foods. This included a range of fatty and lean fish.
During the monitoring period, 205 women were diagnosed with rheumatoid arthritis. Across the entire group, there was a fourfold difference in omega 3 PUFA consumption between the 20% eating the most and the 20% eating the least.
Women who consumed the least included the highest proportion of smokers and the lowest proportion of alcohol drinkers and aspirin takers. Smoking is a risk factor for rheumatoid arthritis while moderate alcohol and aspirin are protective.
Among those who developed the condition, more than one in four (27%) had a dietary omega 3 PUFA intake of less than 0.21g a day, compared with one in five women across the entire group who consumed this amount.
Some 61% of the women consumed the same amount of omega 3 PUFAs and 64% the same amount of fish at both time points.
Those whose intake of omega 3 PUFAs exceeded 0.21g a day, equivalent to at least one serving of fatty fish or four servings of lean fish a week, in both 1987 and 1997, had half the risk (52% lower) of rheumatoid arthritis of women who consumed less in both years.
And regularly eating one or more servings of all types of fish every week for at least 10 years was linked to an overall 29% reduced risk of developing rheumatoid arthritis compared with eating less than one portion a week.
“The inverse association between fish consumption and [rheumatoid arthritis] can be attributed mainly to its content of long chain [omega] 3 PUFAs,” conclude the authors, who add that their findings indicate a potentially important role for these substances in the development of the disease.