Supplement analysis backed by scientific evidence · PT

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Moderate evidenceGeneral health

Cod Liver Oil

Cod liver oil is a cheap, traditional source of EPA, DHA, vitamin D and vitamin A, and it works as a food-based omega-3 and vitamin D supplement. Its specific claims about preventing infections did not hold up in a large randomized trial, and the vitamin A load caps how much you can safely take.

What the science says

  • Provides EPA, DHA and vitamin D in usable amounts Strong evidence

    A standard 5 mL teaspoon supplies roughly 800-1,000 mg combined EPA+DHA plus about 10 mcg (400 IU) vitamin D, so it delivers omega-3 and vitamin D at doses used in clinical trials. For triglyceride lowering and correcting vitamin D deficiency, the evidence supporting those individual nutrients carries over directly.

  • Does not prevent COVID-19 or other respiratory infections Strong evidence

    A quadruple-blinded randomized trial in 34,741 Norwegian adults gave 5 mL/day cod liver oil or placebo for up to six months and found no reduction in SARS-CoV-2 infection, COVID-19 severity, or other acute respiratory infections. Baseline vitamin D status in the cohort was already adequate, which is consistent with meta-analysis data showing vitamin D reduces respiratory infections mainly in people who are deficient.

  • Corrects vitamin D deficiency Moderate evidence

    Individual participant data meta-analysis of 25 vitamin D trials (11,321 participants) found a protective effect against acute respiratory infection driven almost entirely by people with baseline 25(OH)D below 25 nmol/L, where the odds ratio was about 0.30. Cod liver oil is a reasonable delivery vehicle for that correction, but it is a low-dose vitamin D source and pure vitamin D3 is more efficient if that is the goal.

Dosage & safety

Studied dose5 mL (one teaspoon) daily is the traditional dose, providing roughly 800-1,000 mg EPA+DHA, ~10 mcg vitamin D and ~250-800 mcg retinol depending on brand. Do not scale up freely to reach higher omega-3 doses — use plain fish oil instead.
SafetyThe limiting factor is preformed vitamin A (retinol). Cumulative high intake is linked to reduced bone mineral density and liver toxicity, and it is teratogenic — pregnant women should not take unrestricted cod liver oil, and doses should keep total retinol below about 3,000 mcg/day. Avoid stacking with a multivitamin containing retinol. Mild antiplatelet effect at higher omega-3 intakes; disclose before surgery and use caution with anticoagulants. Fishy burps and GI upset are common.

Scientific references

Where to buy

NOW Foods, Cod Liver Oil, 1,000 mg, 180 Softgels

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