The Study
Omega-3 Long-Chain Polyunsaturated Fatty Acid Content and Oxidation State of Fish Oil Supplements in New Zealand
This study didn't test if fish oil makes people healthier — it just checked what's inside the bottles. It's like counting how many apples in a store are ripe, not whether eating them gives you more energy.
Analysis score
Maximum 22 for a cross-sectional study.
Where the score came from
Scientists tested 47 fish oil supplements sold in New Zealand to see if they really had the omega-3s they claimed and if they were spoiled.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 522 / 100
Quality score
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Most fish oil pills are fine — they have the omega-3s they promise, and even when they get a little oxidized, the omega-3s don’t disappear.
- 291% had the right amount of omega-3s (EPA/DHA); 72% were not too oxidized by strict standards; 86% passed secondary oxidation tests — but flavors made some tests falsely show spoilage.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Scientific Reports
Year
2017
Authors
G. Bannenberg, Craig Mallon, H. Edwards, Derek Yeadon, Kevin Yan, Holly Johnson, A. Ismail
Related Content
Claims (6)
Omega-3 fatty acids in dietary supplements break down chemically when exposed to air, heat, or light during production and storage.
Of 47 fish oil supplements tested in New Zealand, 72% met the stricter international standard for oxidation, and 98% met the less strict standard, showing most products met regulatory limits for oxidation.
In a test of 47 fish oil supplements sold in New Zealand, 91% had EPA and DHA concentrations that were within 90% of what was printed on the label when measured using standard laboratory methods.
Fish oil supplements tested one year after their expiration date retained their EPA and DHA levels even though oxidation markers increased, showing that oxidation during normal storage does not significantly reduce omega-3 fatty acid content within the typical shelf life.
The difference in compliance rates between two studies is due to errors in how samples were handled, such as exposure to air or use of incorrect lab materials, and not because the products failed.
Fish oil supplements with a Peroxide Value to p-Anisidine Value ratio above 1 are rare and suggest oxidation happened recently during handling; most supplements have ratios below 1, indicating oxidation occurred before testing.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.