In a recent study, people with rheumatoid arthritis who ate fish at least twice a week reported less swelling and pain than those who rarely or never did. And the findings suggest that the more fish people ate, the less active the disease became. 
The research, published in Arthritis Care & Research, involved 176 people who answered questions about their diet over the past year. The researchers focused on responses to questions about how often participants consumed tuna, salmon, sardines, and other types of fish prepared raw, broiled, steamed, or baked.
Fried fish, shellfish, or fish mixed in dishes (such as stir-fry) were excluded from the study, as these types of meals tend to be lower in omega-3 fatty acids – a substance known for its anti-inflammatory properties.
The researchers also looked at participants’ disease-activity scores, which measured the number of swollen and tender joints they had. It is also a blood marker of inflammation.
After adjusting for a number of factors that may otherwise affect the results, including age, sex, body mass index, depression, marital status, medication use and fish-oil consumption, the disease-activity scores of those who ate the most fish were an average half a point lower than those who rarely or never ate fish. 
The difference is more significant than it looks on a computer screen. See, for the scale used in the study, a score of less than 2.6 indicates remission, while a score greater than 5.1 indicates active disease. According to the researchers, a half-point reduction is clinically significant because it is about 1/3 the amount of improvement reported in clinical trials for methotrexate drugs, considered the standard care for rheumatoid arthritis.
Lead author Dr. Sara Tedeschi, associate physician in rheumatology at Brigham and Women’s Hospital, said:
“With that type of improvement, we would generally expect that a patient would feel noticeably better.”
Past studies have shown that taking fish-oil supplements may help the aches and pains of rheumatoid arthritis, but this is among the first studies to examine the consumption of actual fish.
If you’re not a big fish-eater, it’s cool; the findings suggest that you don’t have to eat fish at least twice a week to reap some of the benefits. You don’t have to cap your fish consumption at twice a week, either, as each serving of fish per week was linked to lower disease activity.
“If our finding holds up in other studies, it suggests that fish consumption may lower inflammation related to rheumatoid arthritis disease activity.
Fish consumption has been noted to have many beneficial health effects, and our findings may give patients with rheumatoid arthritis a strong reason to increase fish consumption.” 
By the way, rheumatoid arthritis is caused by the immune system mistakenly attacking the joints, resulting in pain, swelling, and inflammation. It is a chronic and progressive condition that can affect any joint, but it typically affects the joints in the wrists and hands. Over time, inflammation can cause the cartilage to break down, leading to joint deformities and mobility problems. 
So eat more fish!