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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
Cod Liver Oil doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
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 randomised trials
every one checked individually
Every randomised or controlled trial of Cod Liver Oil indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
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momentum for Cod Liver Oil, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed.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 Oct 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.
Cod liver oil is fish-derived. With fish allergy, do not start an unverified product. Obtain prescriber or allergist advice and check the complete ingredient list. Avoid a product that has caused a reaction.
Tell your prescriber or pharmacist before adding or changing this oil supplement while using a blood thinner. Review the exact product, EPA and DHA content, dose and other ingredients. Do not change the blood thinner yourself. This precaution has no severity grade. The size of any effect for this product has not been established, so it is shown for you to raise with a pharmacist, not as an assessed risk or an all-clear. Do not stop or change prescribed medicines based on this notice.
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 16 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, so check the right dose for you with a healthcare provider.
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 has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. Reported side effects include vitamin A excess (at high doses), fishy aftertaste / burps, mild GI upset / loose stools. How often they occur is not established for all of them. 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.
Black Seed Oil
Likely helpsThymoquinone-rich oil studied for immune modulation, blood sugar control, and anti-inflammatory effects across numerous trials.
Flaxseed
Too few graded studiesA whole food rich in the plant omega-3 ALA, soluble fiber, and lignans. The best-supported benefit is a modest blood-pressure reduction with whole/milled flaxseed (meta-analysis level), with smaller effects on LDL cholesterol and glycemic markers. Menopausal-symptom and lignan effects are weak and inconsistent.
Probiotics
Likely helpsLive microorganisms where strain selection determines outcome — Lactobacillus and Bifidobacterium strains best studied for gut, immune, and mood.
Explore: Best supplements for Vitality & Longevity
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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