Women who regularly get some fish in their diet may have a relatively lower risk of developing rheumatoid arthritis, a large new study suggests.
Swedish researchers found that of the 32 000-plus women they followed for nearly eight years, those who ate fish at least once a week were 29% less likely to develop rheumatoid arthritis than other women.
Fatty fish such as salmon, mackerel and herring seemed to be key, the researchers report in the Annals of Rheumatic Diseases. Those fish contain an inflammation-fighting fat called omega-3, and women who had a higher omega-3 intake showed half the rheumatoid arthritis risk.
The findings do not prove that fish consumption wards off the painful joint disease, experts said. But there is a biological basis to believe that fish could offer some protection: rheumatoid arthritis is caused by a misguided immune system attack on the joints, which leads to chronic and widespread inflammation. Omega-3 fatty acids help ease inflammation.
"This fits a biological model that's very plausible," said Dr Daniel Solomon, a rheumatologist and epidemiologist at Brigham and Women's Hospital in Boston.
Curbing the odds
Solomon, who was not involved in the study, said the findings are also in line with past research linking higher omega-3 intake with lower disease activity in people who already have rheumatoid arthritis.
What's "exciting" about the new findings, he said, is that they suggest that a dietary measure could help curb the odds of developing rheumatoid arthritis in the first place. "Right now, we don't have much in the way of [rheumatoid arthritis] prevention," Solomon said.
He added, though, that this study was not a clinical trial, and "it doesn't prove causation".
Another expert agreed.
"This doesn't mean fish will prevent [rheumatoid arthritis]," said Dr Diane Horowitz, a rheumatologist at North Shore University Hospital in Manhasset, NY, who was not involved in the study.
She said many factors, including genes, are believed to affect a person's risk of developing rheumatoid arthritis. And no one with the disease should "blame themselves" because of their past eating habits, she added.
"There is no one definitive thing that causes it," Horowitz said.
Still, she said, including fish in your diet is a generally healthy move. "If you want to make a healthy dietary change," Horowitz said, "you can have a fish meal instead of meat once a week."
For the study, Alicja Wolk and colleagues at the Karolinska Institute in Stockholm combed data on 32 232 middle-aged and older Swedish women who completed detailed diet questionnaires. Over an average of almost eight years, 205 of those women were diagnosed with rheumatoid arthritis.
Overall, women who said they had fish at least once a week were 29% less likely to develop rheumatoid arthritis than women who ate fish less often. And that was with other factors such as smoking, body weight and some other diet habits taken into account.
The researchers said that the link seemed to be explained by omega-3 intake. They estimated that women who consistently got more than 0.21 grams of omega-3 per day over the years had a 52% lower risk of rheumatoid arthritis than women who consumed less.
And that amount is equivalent to one serving of fatty fish per week or four servings of leaner fish, such as cod.
More fish in your diet
The study looked only at whole fish intake and not fish oil supplements. "We would need more research to know if this would be seen in people using supplements," Solomon said.
Horowitz noted that fish oil can vary in quality. Plus, whole fish provide other nutrients important for overall health, and can take the place of less-healthy choices, such as red meat, she added.
"I think it's better to focus on getting more fish in your diet," Horowitz said.
In the United States, about 1.3 million adults have rheumatoid arthritis, according to the Arthritis Foundation. Women are at greater risk than men, and smokers face a heightened risk.
The best way people can curb their rheumatoid arthritis risk is to not smoke especially if they have a family history of the disease, said Dr Patience White, vice president of public health policy and advocacy for the Arthritis Foundation.
"Fish is good for you, for many reasons," White said. "But I don't want people to think that if they eat fish, they won't develop [rheumatoid arthritis]. It's much more important not to smoke."
She added that a healthy lifestyle, including exercise and maintaining a normal weight, may not help prevent rheumatoid arthritis, but it will put people in a better place to manage the disease if they do develop it.
The Arthritis Foundation has more on rheumatoid arthritis.