Cod Liver Oil
Evidence Fact Sheet
Vitamin A · D · EPA · DHA combined
Cod liver oil is a traditional fish-liver oil delivering EPA/DHA omega-3s plus preformed vitamin A (retinol) and vitamin D3 in one native-triglyceride matrix. Research dose ranges from 5-10 mL/day. Authorized EPA+DHA, vitamin A and vitamin D claims in the EU (Reg 432/2012) and an EPA+DHA triglyceride claim in Brazil (ANVISA); a traditional food / DSHEA supplement in the US.
Also known as: Cod-liver oil · Hippoglossus or Gadus liver oil · CLO
Overview
Cod liver oil is a traditional cold-climate dietary oil pressed from the livers of cod (Gadus) and related fish. Mechanistically it is unusual because it combines long-chain omega-3 fatty acids (EPA and DHA, acting through the omega-3 pathway) with preformed vitamin A (retinol) and vitamin D3 (cholecalciferol) in a single native-triglyceride form that supports absorption. Typical research and commercial doses range from about 5-10 mL/day, historically taken during Northern-latitude winters and during pregnancy when fish intake is low. Regulatory status: a traditional food and DSHEA dietary supplement in the US (with qualified, not authorized, omega-3 health claims); EU EFSA authorizes EPA+DHA heart, vitamin D calcium/phosphorus, and vitamin A vision claims (Reg 432/2012) when per-serving source thresholds are met; Brazil's ANVISA authorizes an EPA+DHA triglyceride claim at >=1,500 mg/day; permitted in China as a traditional food/health-food raw material. Because it contains preformed retinol, per-serving vitamin A content warrants attention in pregnancy.
Mechanism of Action
Combined delivery of EPA/DHA (omega-3 pathway) with preformed vitamin A (retinol) and vitamin D3 (cholecalciferol) · Phospholipid-supported absorption from native triglyceride form · Maternal-to-infant DHA transfer during pregnancy and lactation (Helland 2003)
Body systems: Cardiovascular · BONE · Vision · REPRODUCTIVE
Evidence-Based Benefits
Each benefit below is anchored to a specific PubMed-indexed study. Effect sizes, sample sizes, and p-values are reported as published; no values are inferred. Honest negatives and null results are kept alongside the positive findings, and disease-research populations are described as such — Cod Liver Oil is not characterized as a treatment for any disease.
Acute Respiratory Infections / COVID-19 (Prevention)
Null / no benefit RCT supported- RR 1.00SARS-CoV-2 · 95% CI 0.82-1.22
- RR 1.04acute respiratory infection · 0.97-1.11
In a very large Norwegian winter trial, daily cod liver oil (a low-dose vitamin D source) did not lower the rate of SARS-CoV-2 infection, serious COVID-19, or other acute respiratory infections versus placebo. This is a prominent honest negative for the popular 'cod liver oil prevents winter colds' hypothesis at this dose.
Reported effect: 227 (1.31%) cod liver oil vs 228 (1.32%) placebo positive SARS-CoV-2 (RR 1.00, 95% CI 0.82-1.22); acute respiratory infections 22.94% vs 22.13% (RR 1.04, 0.97-1.11)
“227 (1.31%) participants in the cod liver oil group and 228 (1.32%) participants in the placebo group had a positive SARS-CoV-2 test result (relative risk 1.00, multiple comparison adjusted confidence interval 0.82 to 1.22). ... 3964 (22.94%) and 3834 (22.13%) participants in the cod liver oil and placebo groups, respectively, reported >=1 acute respiratory infections (1.04, 0.97 to 1.11). ... Supplementation with cod liver oil in the winter did not reduce the incidence of SARS-CoV-2 infection, serious covid-19, or other acute respiratory infections compared with placebo.”
Source: PMID 36215222 · Brunvoll 2022 · BMJ
Rheumatoid Arthritis (NSAID-Sparing)
RCT supported- 39% vs 10%NSAID cut >30% · p=0.002
- 19/49 vs 5/48cod liver oil vs placebo
In a 9-month dual-centre, double-blind RCT, more rheumatoid arthritis patients taking cod liver oil were able to cut their daily NSAID requirement by more than 30% than those on placebo. The authors framed cod liver oil n-3 fatty acids as an NSAID-sparing agent in studied RA patients, not a disease cure.
Reported effect: 19/49 (39%) cod liver oil vs 5/48 (10%) placebo reduced daily NSAID requirement by >30% (P=0.002)
“Out of 49 patients 19 (39%) in the cod liver oil group and out of 48 patients 5 (10%) in the placebo group were able to reduce their daily NSAID requirement by >30% (P = 0.002, chi-squared test). ... This study suggests that cod liver oil supplements containing n-3 fatty acids can be used as NSAID-sparing agents in RA patients.”
Source: PMID 18362100 · Galarraga 2008 · Rheumatology (Oxford)
Maternal Supplementation & Infant Cognitive Development
RCT supported- 106.4 vs 102.3Mental Processing · age 4
In a double-blind RCT, children whose mothers took cod liver oil during pregnancy and lactation scored higher on the Kaufman Mental Processing Composite at age 4 than children of mothers given corn oil, and maternal DHA intake was the only variable reaching statistical significance in the regression. This is the card's evidence anchor; it is associational within a small trial, not proof of a guaranteed IQ benefit.
Reported effect: Mental Processing Composite at age 4: 106.4 [7.4] cod liver oil (n=48) vs 102.3 [11.3] corn oil (n=36)
“Children who were born to mothers who had taken cod liver oil (n = 48) during pregnancy and lactation scored higher on the Mental Processing Composite of the K-ABC at 4 years of age as compared with children whose mothers had taken corn oil (n = 36; 106.4 [7.4] vs 102.3 [11.3]). ... In a multiple regression model, maternal intake of DHA during pregnancy was the only variable of statistical significance for the children's mental processing scores at 4 years of age.”
Source: PMID 12509593 · Helland 2003 · Pediatrics
Gestational Diabetes — Metabolic & Inflammatory Markers
RCT supported- 1:1double-blind vs mineral-oil placebo
- P>0.05no 4-week difference
In a 550-patient double-blind placebo-controlled trial in gestational diabetes, cod liver oil showed no separation from placebo at 4 weeks, but over a longer 12-16 week window the abstract reports significantly lower glucose, lipid, HOMA-IR and hs-CRP levels and fewer perinatal complications. The abstract gives outcome direction and p-value thresholds only; it does not report exact mean differences, so no single effect size is extractable.
Effect size: this study reports the direction of the finding but does not state a specific numeric effect size, so none is given here rather than estimated.
“No significant differences between groups for HbA1c, FPG, 2hPG, HOMA-IR, and lipid profiles (P > 0.05) at 4 weeks ... the intervention group showed significantly lower levels versus control for HbA1c, FPG, 2hPG, triglyceride, total cholesterol, LDL-C, HOMA-IR, hs-CRP (P < 0.05) ... Cod-liver oil consumption effectively reduced the levels of blood glucose, lipid levels, hs-CRP, and HOMA-IR and the incidence of perinatal complications.”
Source: PMID 31956660 · Yang 2019 · J Diabetes Res
Dosage (research context · not a recommendation)
10 mL/day cod liver oil during pregnancy from 18 weeks through 3 months postpartum (Helland 2003 PMID 12509593 Pediatrics double-blind RCT n=84 children at age 4 · cod-liver-oil group MPC 106.4 vs corn-oil 102.3 · maternal DHA supplementation associated with higher cognitive performance in offspring); modern commercial doses typically 5-10 mL providing ~1,000-2,500 mg EPA+DHA combined plus ~ 800-1,200 IU vitamin D and ~ 2,500-4,500 IU vitamin A
Regulatory Status · 4 Markets
- US · FDA
- Traditional food / DSHEA dietary supplement (no FDA no-questions GRAS notice specific to cod liver oil) · qualified (not authorized) health claims under the omega-3 framework (EPA+DHA + CHD risk · 2003Q-0401; EPA+DHA + blood pressure · 2014Q-0337); vitamin A and D structure/function claims permitted within DVs
- EU · EFSA
- Authorized claims Reg 432/2012 EPA+DHA cardiovascular, vitamin D calcium-phosphorus, vitamin A vision and immune function — applicable when the source thresholds are met per serving
- CN · China
- Permitted in China as an existing food/health-food raw material: fish/cod-liver oil is a traditional food ingredient and has numerous SAMR health-food registrations (e.g. immune support, blood-lipid). Conventional-food use cannot bear health-function claims.
- BR · ANVISA
- RDC 243/2018 dietary supplement · IN 28/2018 Anexo V alegação funcional verbatim: "Os ácidos graxos ômega 3 EPA e DHA auxiliam na redução dos triglicerídeos." (≥ 1.500 mg EPA+DHA/dia)
Authorized Claims
EFSA — “EPA and DHA contribute to the normal function of the heart.” (Reg 432/2012)
EFSA — “Vitamin D contributes to normal absorption and utilisation of calcium and phosphorus.” (Reg 432/2012)
EFSA — “Vitamin A contributes to the maintenance of normal vision.” (Reg 432/2012)
ANVISA — “Os ácidos graxos ômega 3 EPA e DHA auxiliam na redução dos triglicerídeos.” (IN 28/2018 Anexo V alegação funcional)
Safety
WATCHPOINT: excess preformed vitamin A (retinol) intake in pregnancy can be teratogenic (>10,000 IU/day cumulative) · check the per-serving retinol content before stacking with multivitamins or other vitamin-A sources; vitamin D3 contribution should be counted toward the daily 25(OH)D target; standard fish-allergen disclosure
Related
Goals: heart-health · joint-bone · cognitive-support · reproductive-health
Lifestyles: senior-60-plus · pregnancy
References
PubMed-indexed citations anchoring the benefit findings above. Effect sizes are reported as published.
- PMID 36215222 · Brunvoll 2022 · BMJ — Acute Respiratory Infections / COVID-19 (Prevention)
- PMID 18362100 · Galarraga 2008 · Rheumatology (Oxford) — Rheumatoid Arthritis (NSAID-Sparing)
- PMID 12509593 · Helland 2003 · Pediatrics — Maternal Supplementation & Infant Cognitive Development
- PMID 31956660 · Yang 2019 · J Diabetes Res — Gestational Diabetes — Metabolic & Inflammatory Markers
Frequently Asked Questions
1. What makes cod liver oil different from a plain fish oil?
Cod liver oil delivers EPA and DHA omega-3s together with preformed vitamin A (retinol) and vitamin D3 in one native-triglyceride oil, whereas most body-fat fish oils are concentrated for EPA/DHA without the fat-soluble vitamins. That combined vitamin A + D + omega-3 profile is why it was historically used as winter 'dietary insurance' in cold-climate populations.
2. Is there human evidence in arthritis or pregnancy?
Yes, both are studied. In a 9-month RCT in rheumatoid arthritis, 39% of cod-liver-oil patients cut their daily NSAID use by more than 30% versus 10% on placebo (p=0.002). Separately, in a double-blind pregnancy/lactation trial, children of mothers given cod liver oil scored 106.4 vs 102.3 on a mental-processing composite at age 4, with maternal DHA the only statistically significant predictor. Both are single trials, not proof of disease treatment.
3. Anything to watch for because of the vitamin A?
Because cod liver oil contains preformed vitamin A (retinol), the per-serving retinol amount is worth checking before stacking it with multivitamins or other vitamin-A sources, especially in pregnancy. The vitamin D3 it provides also counts toward total daily vitamin D intake. This is context for interpreting the research, not personalized dosing advice.
Last evidence review: 2026-06-04