NutriDex

The Supplement Research Compendium
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Cod Liver Oil

Gadus morhua

Omega-3s plus vitamins A and D in one traditional fish-liver oil.

Moderate evidence 🫀Heart & Metabolic🍊Vitamin

✚ Updated · How we grade evidence

Evidence tier
Moderate
Research weight
Citations
7 verified / 7
Classification
Heart & Metabolic
❝
What the evidence says. Graded moderate: its omega-3s reliably lower triglycerides and it usefully raises vitamin D, but the few trials testing cod liver oil itself are mostly null (a 34,000-person RCT showed no protection against COVID-19 or respiratory infections) and the diabetes/infection benefits come from observational data only. (Moderate evidence: Several controlled trials; effects real but modest or context-dependent.)

What is Cod Liver Oil?

Cod Liver Oil (Gadus morhua) is a heart and metabolic supplement used for lower blood triglycerides. NutriDex grades the human evidence as Moderate. Cod liver oil is pressed from the liver of Atlantic cod and uniquely combines omega-3 fatty acids (EPA and DHA) with vitamins A and D. Its omega-3s consistently lower blood triglycerides in a dose-dependent way (meta-analyses of fish oil show drops of roughly 15–30 mg/dL at typical doses), and regular use measurably raises serum vitamin D. A 9-month RCT in rheumatoid arthritis found 39% of users cut NSAID use by over 30% without worsening disease. However, the largest direct trial (34,601 adults) found cod liver oil did not prevent COVID-19 or other respiratory infections. Childhood benefits for type 1 diabetes and fewer infections come only from observational and cluster studies, which cannot prove cause. So the nutrients it delivers are genuinely useful, but cod liver oil as a product has not been shown to prevent heart disease or infections.

Purported Benefits

✓Lower blood triglycerides
✓Raise vitamin D status
✓Anti-inflammatory (joint pain)
✓Source of vitamins A & D

Evidence by outcome

The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.

OutcomeEvidenceEffectStudies
Lower blood triglyceridesDose-response meta-analysis of marine omega-3 RCTs shows reliable, dose-dependent triglyceride lowering; effect is from EPA/DHA, not unique to cod liver oil. Strong ↑ benefit · moderate 1
Raise vitamin D statusCross-sectional data show daily use raises serum 25(OH)D, but this is observational, not a controlled trial. Moderate ↑ benefit · moderate 1
Reduce NSAID use in rheumatoid arthritisOne 9-month RCT (n=97) let 39% of users cut NSAIDs >30% without worsening disease; single small trial. Preliminary ↑ benefit · moderate 1
Prevent respiratory infections (incl. COVID-19)Large RCT (n=34,601) found no reduction in SARS-CoV-2 or other acute respiratory infections. Strong — no effect · negligible 1
Lower type 1 diabetes risk in early lifeOnly case-control/observational evidence (OR 0.74); cannot establish causation. Preliminary ↑ benefit 1

Dosing & Compounds

Typical Dose
About 1–2 teaspoons (5–10 mL) daily, providing roughly 1–2 g EPA+DHA plus vitamins A and D; check the label, as vitamin A content limits how much is safe.
Active Compounds
EPA & DHA (omega-3 fatty acids)Vitamin D3 (cholecalciferol)Vitamin A (retinol)

Safety & Cautions

Generally well tolerated; common effects are fishy burps, reflux and loose stools. The main concern is vitamin A: high or stacked doses can cause toxicity (headache, bone pain, liver harm) and excess in pregnancy is teratogenic, so pregnant women should limit retinol intake. Omega-3s and the vitamin D content modestly thin the blood and can add to the effect of anticoagulants/antiplatelets (warfarin, aspirin, DOACs); high doses may also raise LDL cholesterol. Use caution if combining with other vitamin A or D supplements. Educational only — always check with your doctor or pharmacist before combining Cod Liver Oil with any medicine.

Cod Liver Oil drug interactions

Known or theoretical interactions between Cod Liver Oil and common medications — educational, not exhaustive. Always check with your doctor or pharmacist before combining Cod Liver Oil with any medicine.

Caution
Pregnancy
Cod liver oil is high in preformed vitamin A; large amounts during pregnancy can cause birth defects.
Preformed vitamin A (retinol) is teratogenic at high intakes, and cod liver oil can deliver large amounts. MedlinePlus — Vitamin A
Monitor
Blood thinners (warfarin, DOACs)
High-dose cod liver oil may slightly add to bleeding risk alongside blood thinners.
Omega-3 (EPA/DHA) reduce platelet aggregation with mild antithrombotic action that can compound anticoagulants. NIH ODS — Omega-3 Fatty Acids
Monitor
Antiplatelet drugs (aspirin, clopidogrel)
Cod liver oil with aspirin or clopidogrel may modestly increase bleeding tendency at high doses.
EPA/DHA dampen platelet aggregation, adding to the antiplatelet effect of these drugs. NIH ODS — Omega-3 Fatty Acids

Key Studies

Meta-analysis Yang 2024 ✓ Full text
Dose-response meta-analysis of RCTs: marine omega-3s lowered triglycerides dose-dependently, with reductions growing at higher EPA+DHA intakes.
RCT Brunvoll 2022 ✓ PubMed
RCT in 34,601 adults: cod liver oil did not reduce SARS-CoV-2 infection (RR 1.00) or other acute respiratory infections (RR 1.04) over winter.
RCT Linday 2010 ✓ PubMed
Cluster-randomized study in young inner-city children: cod liver oil plus a multivitamin cut upper-respiratory pediatric visits by 36–58% over winter.
RCT Galarraga 2008 ✓ PubMed
9-month double-blind RCT (n=97): 39% of cod liver oil users cut NSAID intake >30% without worsening rheumatoid arthritis activity.
RCT Linday 2004 ✓ PubMed
Randomized pediatric-site study (n=94): daily cod liver oil plus multivitamin-mineral reduced upper-respiratory visits per child per month.
Cohort Eysteinsdottir 2015 ✓ Full text
Cross-sectional study (n=4798 elderly): daily cod liver oil raised serum 25(OH)D (~60 nmol/L) but had only marginal, clinically questionable effect on bone density.
Cohort Stene 2003 ✓ PubMed
Case-control study (545 cases, 1668 controls): cod liver oil in the first year of life linked to lower type 1 diabetes risk (adjusted OR 0.74).
7 sources cited · 7 verified Search all studies on PubMed ↗

Common questions about Cod Liver Oil

What is Cod Liver Oil used for?

Cod Liver Oil is most often taken for Lower blood triglycerides, Raise vitamin D status, Anti-inflammatory (joint pain), Source of vitamins A & D. Omega-3s plus vitamins A and D in one traditional fish-liver oil.

Does Cod Liver Oil work — what does the evidence say?

Moderate evidence. Several controlled trials; effects real but modest or context-dependent. Cod liver oil is pressed from the liver of Atlantic cod and uniquely combines omega-3 fatty acids (EPA and DHA) with vitamins A and D. Its omega-3s consistently lower blood triglycerides in a dose-dependent way (meta-analyses of fish oil show drops of roughly 15–30 mg/dL at typical doses), and regular use measurably raises serum vitamin D. A 9-month RCT in rheumatoid arthritis found 39% of users cut NSAID use by over 30% without worsening disease. However, the largest direct trial (34,601 adults) found cod liver oil did not prevent COVID-19 or other respiratory infections. Childhood benefits for type 1 diabetes and fewer infections come only from observational and cluster studies, which cannot prove cause. So the nutrients it delivers are genuinely useful, but cod liver oil as a product has not been shown to prevent heart disease or infections.

What is the typical dose of Cod Liver Oil?

About 1–2 teaspoons (5–10 mL) daily, providing roughly 1–2 g EPA+DHA plus vitamins A and D; check the label, as vitamin A content limits how much is safe.

Is Cod Liver Oil safe? Any cautions or side effects?

Generally well tolerated; common effects are fishy burps, reflux and loose stools. The main concern is vitamin A: high or stacked doses can cause toxicity (headache, bone pain, liver harm) and excess in pregnancy is teratogenic, so pregnant women should limit retinol intake. Omega-3s and the vitamin D content modestly thin the blood and can add to the effect of anticoagulants/antiplatelets (warfarin, aspirin, DOACs); high doses may also raise LDL cholesterol. Use caution if combining with other vitamin A or D supplements.

How many studies support Cod Liver Oil?

NutriDex cites 7 sources for Cod Liver Oil, graded "Moderate".

Does Cod Liver Oil interact with any medications?

Yes — known or theoretical interactions include: Pregnancy (caution), Blood thinners (warfarin, DOACs) (monitor), Antiplatelet drugs (aspirin, clopidogrel) (monitor). This is educational and not exhaustive; always check with your doctor or pharmacist before combining Cod Liver Oil with any medicine.

Cite this page
APA

Peh, D. (2026). Cod Liver Oil (Gadus morhua): Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 26 Jun 2026, from https://nutridex.info/s/cod-liver-oil

BibTeX
@misc{nutridex_cod_liver_oil,
  author       = {Peh, Daryl},
  title        = {Cod Liver Oil (Gadus morhua): Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/cod-liver-oil},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-06-26}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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