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Cod Liver Oil
A traditional fish-liver oil delivering EPA/DHA omega-3s plus naturally occurring vitamins A and D. The evidence is mixed: a small RCT showed NSAID-sparing benefit in rheumatoid arthritis, but a very large RCT found it did NOT prevent COVID-19 or other respiratory infections. Largely overlaps plain omega-3 fish oil.
What the evidence says
Most Cod Liver Oil studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from high-quality randomised trials published 1983–2025 with a typical study size of 1,156 participants.
Based on 16 studies · 12 RCTs · 1,250 total participants
Confidence
High confidenceBy outcome
Evidence is mixed and condition-specific: one small RCT showed NSAID-sparing benefit in rheumatoid arthritis, but the largest RCT (34,000 adults) found no respiratory protection, and no meta-analyses exist — keeping the score emerging.
17 rigorous studies
17 randomized trials · 0 meta-analyses · 0 systematic reviews
Our evidence rating for Cod Liver Oil is accountable to this entire body of rigorous research indexed in PubMed — not a hand-picked subset.
PubMed · as of Jul 2026
1 trial ongoing or recruiting · 8 completed on ClinicalTrials.gov
1 of the completed trials have posted results
Registered trials show research momentum for Cod Liver Oil, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Sep 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Cod Liver Oil meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Cod liver oil is pressed from the livers of cod (Gadus species) and has been used for over a century, originally to prevent rickets. Unlike standard fish oil (which comes from body tissue), cod liver oil naturally contains fat-soluble vitamins A and D alongside the omega-3 fatty acids EPA and DHA.
Its rationale rests on combining anti-inflammatory omega-3s with vitamin D's immune and bone roles. The honest evidence picture is mixed.
The single best-supported finding is from a small double-blind RCT in rheumatoid arthritis, where cod liver oil let more patients cut their NSAID dose by over 30% — a real but modest NSAID-sparing effect.
A pediatric study linked daily cod liver oil (with a multivitamin) to fewer upper-respiratory clinic visits, and an older Norwegian case-control study associated maternal cod liver oil use with lower offspring type-1 diabetes risk.
However, the largest and most rigorous trial — a quadruple-blinded RCT of over 34,000 Norwegian adults — found cod liver oil did NOT prevent SARS-CoV-2 infection, serious COVID-19, or other acute respiratory infections.
Because its omega-3 content overlaps plain fish oil and its vitamin A content imposes an upper limit, cod liver oil is best seen as a traditional combination product with modest, condition-specific evidence rather than a standout supplement.
Marine omega-3s reduce production of pro-inflammatory eicosanoids and support cardiovascular and membrane function.
Naturally present vitamin D supports immune modulation and bone mineralization, historically used to prevent rickets.
Preformed vitamin A supports vision, epithelial integrity, and immune function — but also imposes an upper intake limit.
How Cod Liver Oil works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Avoid — the NHS advises not taking cod liver oil, or any vitamin A supplement, in pregnancy; preformed vitamin A (retinol) is teratogenic at high intakes. Use a fish-body oil with no vitamin A if you want the omega-3s.
Use with caution and inform your clinician due to omega-3 effects on platelets.
Track total preformed vitamin A intake to avoid toxicity.
Different rule from pregnancy: while nursing, the constraint is total preformed vitamin A. LactMed places maternal daily doses up to 1,500 mcg in the clear and says daily maternal doses above 3,000 mcg should be avoided. Add up every source, including a prenatal or multivitamin.
Omega-3 fatty acids can modestly inhibit platelet function; additive bleeding risk with warfarin, DOACs, or antiplatelet drugs — monitor and inform your clinician.
Cumulative preformed vitamin A can reach toxic levels; avoid stacking with high-dose vitamin A or retinoids.
Cod liver oil already contains vitamin D; account for it when dosing additional vitamin D.
Tip: Take with meals or refrigerate
Tip: Take with food; reduce dose
Tip: Stay within recommended dose; avoid stacking vitamin A sources
Cod Liver Oil has an evidence score of 4/10 — emerging evidence based on 15 indexed studies. A traditional fish-liver oil delivering EPA/DHA omega-3s plus naturally occurring vitamins A and D. The evidence is mixed: a small RCT showed NSAID-sparing benefit in rheumatoid arthritis, but a very large RCT found it did NOT prevent COVID-19 or other respiratory infections. Largely overlaps plain omega-3 fish oil. Representative study: PMID 36215222.
The commonly studied dose of Cod Liver Oil is 5 mL/day (about 1 teaspoon), providing roughly 1-2g omega-3 plus modest vitamins A and D. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Cod Liver Oil is with meals. Take it with food. Taking with a fat-containing meal improves absorption of the omega-3s and fat-soluble vitamins and reduces fishy reflux.
Cod Liver Oil is generally safe at recommended doses, with a few precautions worth noting. The most commonly reported side effects are fishy aftertaste / burps, mild GI upset / loose stools, vitamin A excess (at high doses). Use caution if any of these apply to you: Hypervitaminosis A; Concurrent high-dose vitamin A supplements; Pregnancy — the NHS advises not taking cod liver oil, or any vitamin A supplement, while pregnant.
Omega-3
Probably helpsEssential fatty acids critical for brain health, mood regulation, and reducing inflammation throughout the body.
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Likely helpsThymoquinone-rich oil studied for immune modulation, blood sugar control, and anti-inflammatory effects across numerous trials.
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Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 16 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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