Cod Liver Oil
Also known as: fish liver oil, CLO, omega-3 fish oil, EPA/DHA supplement, vitamin A/D oil
Effective Dosage
5 mL/day liquid or equivalent capsule form based on available studies
What the Science Says
Cod liver oil is an oil extracted from the livers of cod fish, naturally rich in omega-3 fatty acids (EPA and DHA) as well as vitamins A and D. In a large clinical trial of over 34,000 adults, it did not reduce COVID-19 or respiratory infections, but a smaller RCT in gestational diabetes patients found it reduced blood glucose, inflammation markers (hs-CRP), and insulin resistance after 12–16 weeks. Animal studies suggest its omega-3 content may have anti-tumor and neuroprotective effects, though these findings have not been confirmed in humans.
What It Doesn't Do
Won't prevent COVID-19 or common colds — a massive 34,000-person trial found zero benefit. Not proven to treat Alzheimer's disease in humans. No solid evidence it improves menopausal symptoms on its own. Don't expect it to replace your vitamin D supplement — the dose in most cod liver oil products is too low to meaningfully raise levels.
Evidence-Based Benefits
Cod liver oil is an oil extracted from the livers of cod fish, naturally rich in omega-3 fatty acids (EPA and DHA) as well as vitamins A and D. In a large clinical trial of over 34,000 adults, it did not reduce COVID-19 or respiratory infections, but a smaller RCT in gestational diabetes patients found it reduced blood glucose, inflammation markers (hs-CRP), and insulin resistance after 12–16 weeks. Animal studies suggest its omega-3 content may have anti-tumor and neuroprotective effects, though these findings have not been confirmed in humans.
Weak EvidenceEffective at: 5 mL/day liquid or equivalent capsule form based on available studies
Source: auto-research
Absorption & Bioavailability
Good — omega-3 fatty acids from fish oil are generally well absorbed, especially when taken with food. Vitamins A and D are fat-soluble and absorbed alongside the oil itself.
Red Flags to Watch For
- Mercury contamination is possible — always choose products tested for heavy metals; one study found cod liver oil had lower mercury than vegetable oils but contamination still exists
- Vitamin A toxicity risk with high doses — cod liver oil contains preformed vitamin A, which can accumulate to toxic levels if taken alongside other vitamin A supplements or fortified foods
- Low vitamin D content — typical doses provide only ~10 µg (400 IU) vitamin D, which may be insufficient for people who are deficient
- Animal and lab findings (cancer, brain health) have not been replicated in human clinical trials — do not interpret these as proven human benefits
- Quality varies widely across brands — the 1,000+ registered supplement products mean formulations differ significantly in EPA, DHA, and vitamin content
Products Containing Cod Liver Oil
See how Cod Liver Oil is used in these analyzed products:
Research Sources
- PubMed
- NIH DSLD
This information is for educational purposes only and is not medical advice. Always consult a healthcare professional before starting any supplement regimen. Last updated: 2026-04-10