The results of the study by Stammers and colleagues31 must be examined critically, as the likelihood of detection bias is high. Highly subjective assessments of effect, lack of standardized NSAID treatments, and limitations in patient numbers and disease severity raise concerns about validity. In addition, confounding variables (eg, medication interactions, alternative treatments, olive oil use) undermine the design. It is therefore difficult to interpret the results of this trial.
The study by Wang and colleagues30 did not involve supplementation, and intake was assessed only with food frequency questionnaires. It is therefore difficult to apply their results or findings to this review. In addition, the authors did not obtain baseline magnetic resonance imaging for comparison with that obtained at study completion—that is, they did not address any subclinical disease before dietary recording.
Pritchett20 acknowledged study limitations of small sample size and use of 1 subject as both patient and control. Although the study seemed to demonstrate that omega-3 supplementation augmented the lipid profile of joints, it did not directly demonstrate improvement in or prevention of OA. Identification of bone marrow lesions is not definitive proof of OA but an alteration that may correlate with development. The logical supposition is that altering the local environment may alter development of disease within that environment, though this is not proven.
An article reviewing the Phytalgic study highlighted the suspect nature of its results—claims that the supplement is 76% more effective than gold-standard corticosteroid injection.35 Also highlighted were lack of confirmed mechanism, questionable control, detection bias caused by aftertaste, and the high attrition rate in the placebo group. It is difficult to apply these results to fish oil supplementation, as Phytalgic contains other potentially confounding substances.
Of note, the findings of MOST were observational; n-3 and n-6 levels were not altered or supplemented. Altered disease process was demonstrated in patellofemoral cartilage but not in tibiofemoral cartilage in the same patient. The inconsistencies may be explained by the observational nature of the study and the lack of supplementation that would have produced a more significant increase in n-3 PUFA levels and thus more uniform conclusions, if in fact n-3 PUFAs were the significant factor in the altered cartilage structure. Although supportive of a preventive or disease-altering benefit, the results do not speak to supplementation.
Perhaps the most convincing evidence supporting fish oil for OA comes from a 2009 study by Gruenwald and colleagues.33 However, this 2-supplement study addressing synergy was financed by Seven Seas, a company with industry ties. The study was not placebo-controlled and was registered only after completion. The authors omitted baseline values, apparently did not correct for baseline in the statistical analysis, and did not report the distribution of results. The implication is that the results were overstated, or that, at minimum, the supporting data were not reported. Nevertheless, this study demonstrated benefits consistent with the animal and human laboratory studies. However, research is needed to repeat and validate these results, elucidate the mechanism of action, and quantify the benefit unique to fish oil.
Conclusion
Despite the overwhelming popularity of fish oil supplements and the assumption of benefit for patients with arthritis, there appears to be insufficient clinical evidence to justify use of fish oils in the treatment or prevention of OA. Possible efficacy in laboratory and animal studies has yet to be sufficiently observed and verified in clinical trials. Although it is impossible to refute the promise of these agents as beneficial adjuncts to anti-inflammatory regimens, there remains a need for significant, well-designed clinical trials to evaluate the efficacy, safety, and clinical parameters of omega-3 fatty acids in a standardized form before they can in good faith be recommended to patients with OA.