Fish oil helps your joints

For rheumatoid arthritis, fish oil may ease joint symptoms slightly, though the recent reviews disagree on whether the effect is real. For osteoarthritis, the largest trial found no effect on knee pain. A 2024 review limited to placebo-controlled trials pooled 23 trials in rheumatoid arthritis and found small reductions in pain and in tender and swollen joints that were not statistically significant, with the certainty of the evidence rated mostly low or very low. A second 2024 review of 18 trials (1,018 people) found fewer tender joints, but no significant change in overall disease activity scores or in blood markers of inflammation.

In the rheumatoid arthritis trials, fish oil was taken alongside usual arthritis medicines rather than instead of them. The UK clinical guideline for rheumatoid arthritis states that there is no strong evidence that changing diet helps the arthritis, and that complementary therapies should not replace conventional treatment. For osteoarthritis, a 2023 review of nine trials (2,070 people) found a small reduction in pain, but more than half of the people in it came from one US trial, VITAL, in which 1,398 older adults with chronic knee pain took 840 mg a day for about five years and reported no difference from placebo in pain, stiffness or function.

Older trials, many run in the 1990s, reported that people with rheumatoid arthritis taking fish oil used fewer anti-inflammatory painkillers. The US Office of Dietary Supplements summarises that research as generally showing reduced use of anti-inflammatory drugs and corticosteroids, without consistent effects on painful or swollen joints or morning stiffness. The 2024 placebo-controlled review found the reduction in painkiller use small and not statistically significant, and its authors suggest earlier findings may have been biased by inadequate blinding.

The trials did not all test the same thing. The 18-trial review also pooled trials of flaxseed, plant-based alpha-linolenic acid and blue mussel, not only fish oil, and the nine osteoarthritis trials included two of krill oil and one of a green-lipped mussel extract. Krill oil is a different marine source of the same omega-3 fats. In a 2024 Australian trial published after that review, 262 people with knee osteoarthritis and signs of joint inflammation on a scan took 2 g of krill oil a day (580 mg of EPA and DHA) or placebo for 24 weeks, and knee pain fell by about the same amount in both groups.

Doses varied widely. The rheumatoid arthritis trials the Office of Dietary Supplements describes used about 3 to 3.3 g of EPA and DHA a day, and a review of how these fats act on inflammation estimates that more than 2 g a day seems to be needed for anti-inflammatory effects, though few dose-finding studies exist. The osteoarthritis trials in the 2023 review used 350 to 2,400 mg of omega-3 a day, and that review found larger pain improvements in people under 65 than in those 65 and over.

Side effects in the osteoarthritis trials occurred at similar rates with the supplement and placebo, with no severe treatment-related events reported. Fish oil can affect blood clotting. The label for Lovaza, a prescription omega-3 product approved in the US only to lower very high triglycerides, states that some trials found longer bleeding times that stayed within normal limits and did not cause clinically significant bleeding, and that its use with anticoagulants has not been thoroughly studied. The label also advises caution for people allergic to fish or shellfish. The krill oil trial excluded people with a seafood allergy and people taking anticoagulants. The Office of Dietary Supplements notes that fish oil might prolong clotting times with warfarin, while most research finds 3 to 6 g a day does not significantly change anticoagulation.