Cod liver oil
Summary
Cod liver oil supplies omega-3 fats plus vitamins A and D. A trial of 34,601 Norwegian adults found 5 mL a day did not reduce covid-19 or other respiratory infections. In rheumatoid arthritis, 10 g a day helped more people cut painkiller use (grade D), but it did not help osteoarthritis. Its vitamin A content can exceed the adult upper limit.
Key facts
- About 34 mcg (1,360 IU) per tablespoon in the USDA reference oil[3]
- USDA reference oil has about 30,000 mcg RAE per 100 g; the adult upper limit for preformed vitamin A is 3,000 mcg/day[1][2]
- No reduction in covid-19 or other acute respiratory infections in 34,601 adults over a winter[5]
- More patients reduced NSAID use (39% vs 10%) over 9 months[6]
- 5 graded human outcomes on this page
- October 13, 2026
How it works
ProposedCod liver oil supplies the long-chain omega-3 fats EPA and DHA, which the rheumatoid arthritis trial authors describe as having anti-inflammatory and NSAID-sparing properties. It also supplies preformed vitamin A, which the body stores mainly in the liver, and vitamin D.[4][6][2][3]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Pregnancy | Grade D | Mixed | RCT · n = 550 · 2019 | 1 row |
| Joints | Grade D | Improved | RCT · n = 97 · 2008 | 2 rows |
| Respiratory infections | Grade D | Improved | RCT · n = 94 · 2004 | 2 rows |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Blood sugar and lipids in gestational diabetes | Mixed | Grade D | RCT · n = 550 · 2019 Pregnant women with gestational diabetes on usual dietary care Form: Cod liver oil with 76 mg/mL EPA and 150 mg/mL DHA (mineral-oil placebo) · Dose: Dose not stated in the abstract · Duration: 4 weeks (primary), 12–16 weeks (secondary) Primary outcomes (HbA1c, fasting and 2-hour glucose, insulin resistance, lipids) did not differ at 4 weeks. Secondary measures at 12–16 weeks, including glucose, lipids, hs-CRP and perinatal complications, were lower with cod liver oil. | 31956660 (opens PubMed)Source [8] |
| Cutting anti-inflammatory painkiller use in rheumatoid arthritis | Improved | Grade D | RCT · n = 97 · 2008 Adults with rheumatoid arthritis on NSAIDs Form: Cod liver oil capsules with 2.2 g omega-3 fatty acids · Dose: 10 g/day · Duration: 9 months 39% of the cod liver oil group versus 10% on placebo cut daily NSAID use by more than 30% (P=0.002). Disease-activity measures and side effects did not differ. | 18362100 (opens PubMed)Source [6] |
| Doctor visits for upper respiratory infections in young children (with a multivitamin) | Improved | Grade D | RCT · n = 94 · 2004 Children aged 6 months to 5 years at two inner-city pediatric practices (New York City) Form: Lemon-flavored cod liver oil plus half a children's multivitamin with selenium · Dose: 1 teaspoon/day (half for under 1 year) · Duration: About 5–6 months (late autumn to spring) Upper respiratory visits trended down over the season at the supplement practice (within-site trend, P=0.042) and did not change at the control practice; no direct between-group test is reported. Only two practices were randomized, and children also took a multivitamin with selenium. | 15562899 (opens PubMed)Source [9] |
| Joint pain in osteoarthritis (added to NSAIDs) | No effect | Grade D | RCT · n = 86 · 1992 Adults with osteoarthritis in general practice Form: Cod liver oil (olive oil placebo) · Dose: 10 mL/day · Duration: 24 weeks No significant benefit for pain, inflammation or daily interference versus placebo. | 1540019 (opens PubMed)Source [7] |
| Covid-19 and other acute respiratory infections in winter | No effect | No effect | RCT · n = 34,601 · 2022 Adults aged 18–75 in Norway not taking daily vitamin D Form: Cod liver oil (10 µg vitamin D per 5 mL) · Dose: 5 mL/day · Duration: Up to 6 months (median 164 days) No reduction in positive SARS-CoV-2 tests (RR 1.00), serious covid-19 (RR 1.20, not significant) or other acute respiratory infections (RR 1.04) versus placebo. Only low-grade side effects in either group. | 36215222 (opens PubMed)Source [5] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Liquid cod liver oil | Varies[1][5] | USDA reference oil contains per 100 g about 30,000 mcg RAE vitamin A, 250 mcg vitamin D, 6.9 g EPA and 11.0 g DHA; commercial products vary.[1][5] | Only low-grade side effects at 5 mL/day over a median 164 days in 34,601 adults.[5] | Respiratory infection, osteoarthritis and child-health trials (1 tsp to 10 mL/day) |
| Cod liver oil capsules | Varies[6] | Capsule content varies by product; the rheumatoid arthritis trial used 10 g/day with 2.2 g omega-3s.[6] | Side effects did not differ from placebo over 9 months.[6] | Rheumatoid arthritis trial |
Studied doses
Doses studied in human trials ranged from 1 teaspoon (about 5 mL) a day in young children and 5 mL/day in adults up to 10 mL or 10 g/day, for 4 weeks up to 9 months.[9][5][7][6][8]
Intake reference: Cod liver oil counts toward vitamin A and vitamin D limits. The adult UL for preformed vitamin A is 3,000 mcg RAE/day (lower for children), and for vitamin D 100 mcg (4,000 IU)/day. ODS advises pregnant or lactating women not to take more than 3,000 mcg RAE of vitamin A daily from supplements.[2][3] 3 mg (3,000 mcg) preformed vitamin A per day for adults 19+; children's limits range from 600 to 2,800 mcg. NIH ODS fact sheet (updated March 10, 2025).
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- Oral retinoidsNIH fact sheetRetinoids taken with vitamin A supplements raise the risk of vitamin A toxicity.[2]
- OrlistatNIH fact sheetOrlistat can lower absorption of vitamin A and other fat-soluble vitamins.[2]
- Warfarin and other anticoagulantsNIH fact sheetFish oil has antiplatelet effects at high doses and might raise INR with warfarin, although most research finds 3–6 g/day of fish oil does not significantly change anticoagulation.[4]
Who should be careful
- Pregnancy
- Preformed vitamin A above the upper limit can cause birth defects; ODS advises no more than 3,000 mcg RAE/day from supplements in pregnancy and lactation. Check the vitamin A per serving on the label.[2]
- Children
- Upper limits for vitamin A are lower in children (600–1,700 mcg for ages 0–13), so adult servings can exceed them.[2]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
How to read the label
- Check vitamin A and D per servingVitamin A and D vary widely between products; the 2022 trial oil gave 10 µg vitamin D per 5 mL, below the USDA reference oil.[5][1][3]
- Not the same as fish oilRegular fish oil supplies EPA and DHA without significant vitamin A or D; cod liver oil supplies all three.[4]
- Studied amountsAdult trials used 5–10 mL a day.[5][7][6]
Frequently asked questions
Is cod liver oil the same as fish oil?
No. Both supply EPA and DHA omega-3s, but cod liver oil also provides vitamin A and vitamin D.[4]
Does cod liver oil stop colds or covid-19?
In a winter trial of 34,601 adults, 5 mL a day did not reduce covid-19 or other acute respiratory infections compared with placebo.[5]
Can cod liver oil help arthritis?
In rheumatoid arthritis, 10 g a day for 9 months helped more people cut NSAID use (39% vs 10%). In osteoarthritis, 10 mL a day added nothing over placebo.[6][7]
Can you get too much vitamin A from cod liver oil?
Yes. USDA reference oil has about 4,080 mcg RAE per tablespoon, above the 3,000 mcg adult upper limit. Products vary, so check the label.[1][2]
Is cod liver oil safe in pregnancy?
High preformed vitamin A can cause birth defects, so ODS advises staying at or below 3,000 mcg RAE a day from supplements during pregnancy.[2]
Sources
- [1]Fish oil, cod liver (FDC ID 173577, SR Legacy). USDA FoodData Central, 2018. database
- [2]Vitamin A and Carotenoids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025. fact-sheet
- [3]Vitamin D: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025. fact-sheet
- [4]Omega-3 Fatty Acids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025. fact-sheet
- [5]Prevention of covid-19 and other acute respiratory infections with cod liver oil supplementation, a low dose vitamin D supplement: quadruple blinded, randomised placebo controlled trial.. BMJ, 2022. RCT
- [6]Cod liver oil (n-3 fatty acids) as an non-steroidal anti-inflammatory drug sparing agent in rheumatoid arthritis.. Rheumatology (Oxford), 2008. RCT
- [7]Efficacy of cod liver oil as an adjunct to non-steroidal anti-inflammatory drug treatment in the management of osteoarthritis in general practice.. Ann Rheum Dis, 1992. RCT
- [8]Cod-Liver Oil Improves Metabolic Indices and hs-CRP Levels in Gestational Diabetes Mellitus Patients: A Double-Blind Randomized Controlled Trial.. J Diabetes Res, 2019. RCT
- [9]Effect of daily cod liver oil and a multivitamin-mineral supplement with selenium on upper respiratory tract pediatric visits by young, inner-city, Latino children: randomized pediatric sites.. Ann Otol Rhinol Laryngol, 2004. RCT
What changed
- Independent adversarial review: added the warfarin/anticoagulant interaction from the ODS omega-3 fact sheet, with its caveat that 3–6 g/day usually does not change INR significantly.
- Adversarial review pass: every evidence row's numbers re-checked against its abstract (Europe PMC for abstracts PubMed truncates, PMC full text where open), grades checked against the grading rubric, and safety and overclaim wording re-read. Fixes: Children's respiratory-visit row reworded as a within-site trend with a multivitamin co-intervention and only two randomized practices; rheumatoid-arthritis NSAID row regraded C to D (single 97-person trial, 40% dropout) and the summary updated.
- First draft. Every PMID checked against NCBI E-utilities esummary (title and year taken from the record) and abstracts read for the cited rows.
- Strict second-pass self review (no separate reviewer agent was available for this batch): every PMID re-fetched via esummary and every evidence row, dose and safety line re-read against its abstract or fact sheet. Vitamin A and D figures checked against USDA FoodData Central (FDC 173577) and the ODS vitamin A (updated March 10, 2025), vitamin D (June 27, 2025) and omega-3 (August 22, 2025) fact sheets. Duplicate check: the omega-3 monograph covers fish, krill and algal oil, but not cod liver oil's vitamin A and D, so this page focuses on that difference. Retraction and erratum flags checked on all PMIDs: none.