Krill oil is sometimes used to support rheumatoid arthritis (RA) primarily due to its content of omega-3 fatty acids, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which have known anti-inflammatory properties. Scientific interest in krill oil emerged as a result of studies on fish oil and its potential to reduce inflammation in joint diseases. Some small clinical studies have suggested that krill oil may reduce C-reactive protein levels, a marker of inflammation, and may offer symptomatic relief in arthritis. For example, a 2007 pilot study (Bunea et al., J Am Coll Nutr. 2004) found that krill oil supplementation reduced pain, stiffness, and functional impairment in patients with arthritis symptoms, though the sample size was small and the study included mixed types of arthritis, not only RA.

However, the evidence base is still limited and not robust. Larger, high-quality randomized controlled trials specifically focused on RA patients are lacking. Most existing research is extrapolated from fish oil studies or involves small numbers of participants and short study durations. Current guidelines from major rheumatology organizations do not recommend krill oil as a primary treatment for RA, though they acknowledge that omega-3 supplements may have adjunctive benefits. Overall, while krill oil shows some promise in reducing inflammation, the scientific support for its use in RA is modest, and more rigorous research is needed.