Researchers looked at the diet more than 32,000 Swedish women and found that a fishy diet is beneficial because the omega-3 content is a good anti-inflammatory agent, and as such helps to combat arthritis
Halved risk of arthritis
In the study, which spanned a decade, women who consistently ate any type of fish at least once a week cut their risk of developing rheumatoid arthritis by nearly a third.
And those who ate at least one portion of oily fish or four servings of other fish each week halved their risk.
Prof Alan Silman, medical director of Arthritis Research UK, said: "We've known for some time that there is good evidence that, in people with active arthritis, taking fish oils can reduce the level of inflammation."
Oily fish diets
He advocated taking high levels of fish oils to prevent inflammation from starting in the joint but is concerned about the "substantial pressure this might place on people's diets".
Some white fish and shellfish also contain omega-3 but not as much as oily fish. Public Health England suggest a healthy diet should include at least two portions of fish a week, including one of oily fish.
The study did not look at fish oil supplements, but experts say these may also be beneficial. Rheumatoid arthritis affects more than 580,000 people in England and Wales. As the disease progresses, the immune system attacks the joints, making them stiff, swollen and painful.