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Cod Liver Oil

Gadus morhua
Evidence Level
Moderate
4 Clinical Trials
5 Documented Benefits
3/5 Evidence Score

Cod liver oil is oil from the liver of Atlantic cod. Unlike ordinary fish oil it is naturally rich in preformed vitamin A and vitamin D as well as the omega-3 fats EPA and DHA. USDA's reference value for generic cod liver oil is about 1,350 mcg RAE (4,500 IU) of vitamin A, 450 IU of vitamin D and roughly 800 mg of EPA plus DHA per teaspoon (4.5 g). Many modern refined products are standardized far lower in vitamin A (labels we checked list 40 to 255 mcg RAE per 5 mL), so check the label. It was the classic winter vitamin D source in northern Europe, and users tend to have better vitamin D status. Controlled trials of cod liver oil itself are few: they show lower platelet stickiness with little change in blood lipids, and in people with rheumatoid arthritis it let more patients cut back on pain medicine. The vitamin A content sets the safe limit: high intakes of preformed vitamin A are linked to birth defects, so pregnant women should not exceed 10,000 IU a day.

Studied Dose USDA generic value: 1 tsp (4.5 g) gives about 4,500 IU vitamin A (branded oils often list far less, so use your label's figure), 450 IU vitamin D and 800 mg EPA plus DHA. Trials used 10 g a day (arthritis), 15 mL a day (14 months) and 25 mL a day (8 weeks). Count the vitamin A toward the 10,000 IU adult limit.
Active Compound EPA and DHA (omega-3 fatty acids), preformed vitamin A (retinol and retinyl esters) and vitamin D3 (cholecalciferol).

Benefits

Combined EPA/DHA, vitamin A and vitamin D source

One product supplies omega-3 EPA and DHA plus preformed vitamin A and vitamin D, which ordinary fish oil lacks. By USDA's generic value one teaspoon gives about 450 IU of vitamin D and 4,500 IU of vitamin A (many refined brands list much less vitamin A), so the vitamin A, not the omega-3, usually limits how much can safely be taken.

Supported by Trial 4

Vitamin D status for bone health

Vitamin D helps the body absorb calcium and keep bones mineralized. In observational studies from Scotland and Iceland, users had better vitamin D status, but lifelong use was not linked to hip bone density. In a 2-year trial in 1,144 nursing home residents, 5 mL a day raised vitamin D levels but did not lower fractures versus oil with the vitamin D removed.

Supported by Trial 4

Vision support (vitamin A)

Vitamin A is an essential part of rhodopsin, the light-sensing pigment of the retina, and supports the cornea. The first sign of deficiency is poor vision in dim light. Cod liver oil is a concentrated source, which matters mainly when diets are short of vitamin A.

Supported by Trial 4, Trial 1

Omega-3 (EPA and DHA) content

Cod liver oil supplies the same EPA and DHA as fish oil. A Cochrane review of 79 trials in over 112,000 people found that long-chain omega-3 supplements have little or no effect on heart attacks, strokes or deaths. In a Norwegian cohort of 42,612 adults, cod liver oil use was not linked to deaths from heart disease.

Supported by Trial 1, Trial 2

Lower platelet aggregation markers, little change in blood lipids

Studied at 15 to 25 mL a day, 3 to 5 times a teaspoon. In 34 healthy adults over 8 weeks, thromboxane B2 fell, triglycerides fell only in men and LDL rose in men. Over 14 months in 120 adults with high cholesterol, cod or seal oil lowered platelet aggregation without changing cholesterol. An observational cohort of 42,612 Norwegians found no link to heart disease deaths.

Supported by Trial 3, Trial 2

Mechanism of action

1

Vitamin A (retinol)

Preformed vitamin A forms part of rhodopsin in the retina and supports the cornea, cell growth and immune function. The body stores excess vitamin A in the liver, so it can build up with regular high intakes.

2

Vitamin D3 (cholecalciferol)

Vitamin D promotes calcium absorption in the gut and is needed for bone growth and remodeling. Without enough of it bones can become thin, brittle or misshapen.

3

EPA and DHA

These omega-3 fats are built into cell membranes and are converted into signaling molecules that affect platelet function; in cod liver oil trials, platelet aggregation and thromboxane B2 fell.

Clinical trials

1
Cod Liver Oil and NSAID Use in Rheumatoid Arthritis
PubMed

Dual-centre, double-blind, placebo-controlled randomized trial of 10 g a day of cod liver oil (2.2 g omega-3 fats) for 9 months, with patients asked to cut their NSAID use from week 12. (Galarraga et al. 2008, Rheumatology (Oxford))

97 adults with rheumatoid arthritis; 58 completed.

39% of the cod liver oil group cut daily NSAID use by more than 30%, versus 10% on placebo (P = 0.002). Disease activity and side effects did not differ between groups.

2
Cod Liver Oil and Seal Oil Over 14 Months
PubMed

Randomized trial of 15 mL a day of seal oil or cod liver oil for 14 months, with a third group taking no supplement. (Brox et al. 2001, Lipids)

120 clinically healthy adults with total cholesterol of 7.0 to 9.5 mmol/L.

Both oils lowered whole-blood platelet aggregation versus no supplement. Neither changed total cholesterol, HDL, post-meal triglycerides, apolipoproteins or lipoprotein(a).

3
Cod Liver Oil, Lipids and Platelets in Men and Women
PubMed

Controlled crossover study of 25 mL a day of cod liver oil for 8 weeks. (Hansen et al. 1993, Eur J Clin Nutr)

34 healthy non-smoking adults (20 men, 14 women).

Thromboxane B2 generation fell in both sexes. Triglycerides fell by 0.21 mmol/L in men only, LDL cholesterol rose by 0.28 mmol/L in men, and HDL did not change.

4
Vitamin D in Cod Liver Oil and Fractures in Nursing Homes
PubMed

Double-blind randomized controlled trial of 5 mL a day of ordinary cod liver oil (10 mcg vitamin D3) versus cod liver oil with the vitamin D removed, for 2 years. (Meyer et al. 2002, J Bone Miner Res)

1,144 residents of 51 nursing homes in Norway.

Blood vitamin D rose by 22 nmol/L more than in the control group, but hip fractures (50 vs 47 people) and all nonvertebral fractures (69 vs 76 people) did not differ.

Side effects and drug interactions

Common Potential side effects

Vitamin A excess: regular high intakes can cause dry skin, painful muscles and joints, fatigue and abnormal liver tests; very high single doses cause severe headache, blurred vision and nausea.
Pregnancy: high intakes of preformed vitamin A are linked to birth defects, and experts advise pregnant and breastfeeding women not to take more than 10,000 IU a day from supplements.
Vitamin D excess: the adult upper limit is 4,000 IU a day from all sources combined, so count cod liver oil toward that total.
Lower platelet aggregation was seen in trials, which may matter for people with bleeding problems.

Important Drug interactions

Retinoid medicines (such as acitretin or bexarotene): raise the risk of vitamin A toxicity when combined with vitamin A sources.
Other vitamin A and vitamin D supplements, including multivitamins: add up toward the upper limits.
Orlistat: reduces absorption of vitamin A and other fat-soluble vitamins.
Blood thinners and antiplatelet drugs: cod liver oil lowered platelet aggregation in trials; ask your doctor before combining.

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Frequently asked questions about Cod Liver Oil

What is cod liver oil?

Oil from cod livers that supplies omega-3 EPA and DHA plus natural vitamin A and vitamin D. It was a traditional winter vitamin D source in northern Europe.

What is cod liver oil good for?

Users tend to have better vitamin D status, and it also supplies vitamin A and omega-3 fats. Large reviews have not shown that omega-3 supplements prevent heart attacks or strokes, and in a nursing home trial its vitamin D did not lower fractures.

How much cod liver oil should I take, and is the vitamin A a concern?

Follow the label and check the vitamin A per serving. Vitamin A varies widely: USDA's generic value is about 4,500 IU per teaspoon, close to half the 10,000 IU adult upper limit, while refined brands we checked list far less, so avoid stacking it with other vitamin A sources, especially in pregnancy.

Is cod liver oil safe?

At labeled doses it is generally used safely. The main risks are vitamin A and vitamin D excess with large or combined doses, and it lowered platelet aggregation in trials, so check with your doctor if you take blood thinners.

What is Cod Liver Oil used for?

Cod Liver Oil is researched primarily for Cardiovascular, Bone Health, and Eye Health. One product supplies omega-3 EPA and DHA plus preformed vitamin A and vitamin D, which ordinary fish oil lacks. By USDA's generic value one teaspoon gives about 450 IU of vitamin D and 4,500 IU of vitamin A (many refined brands list much le…

Does Cod Liver Oil interact with any medications?

Possible interactions include: Retinoid medicines (such as acitretin or bexarotene): raise the risk of vitamin A toxicity when combined with vitamin A sources. Other vitamin A and vitamin D supplements, including multivitamins: add up toward the upper limits. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Cod Liver Oil?

NutraSmarts rates the evidence for Cod Liver Oil as Moderate (3 out of 5). It is backed by 4 study summaries and 13 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(13 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Rajakumar K. Vitamin D, cod-liver oil, sunlight, and rickets: a historical perspective. Pediatrics. 2003;112(2):e132-5. doi: 10.1542/peds.112.2.e132.PubMedUsed to support: Historical review of how cod liver oil and sunlight came to be used against rickets in the early 20th century and how vitamin D was identified.
  2. Galarraga B, Ho M, Youssef HM, Hill A, McMahon H, Hall C, Ogston S, Nuki G, Belch JJ. Cod liver oil (n-3 fatty acids) as an non-steroidal anti-inflammatory drug sparing agent in rheumatoid arthritis. Rheumatology (Oxford). 2008;47(5):665-9. doi: 10.1093/rheumatology/ken024.PubMedUsed to support: Double-blind randomized trial in 97 adults with rheumatoid arthritis (58 completed): 10 g a day of cod liver oil (2.2 g omega-3) for 9 months let 39% cut daily NSAID use by more than 30% versus 10% on placebo (P = 0.002); disease activity and side effects did not differ.
  3. Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ, Deane KH, AlAbdulghafoor FK, Summerbell CD, Worthington HV, Song F, Hooper L. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2018;11(11):CD003177. doi: 10.1002/14651858.CD003177.pub4.PubMedUsed to support: Cochrane review of 79 randomized trials (over 112,000 people): long-chain omega-3 supplements have little or no effect on cardiovascular events, coronary deaths, strokes or all-cause mortality.
  4. Rothman KJ, Moore LL, Singer MR, Nguyen US, Mannino S, Milunsky A. Teratogenicity of high vitamin A intake. N Engl J Med. 1995;333(21):1369-73. doi: 10.1056/NEJM199511233332101.PubMedUsed to support: Cohort of 22,748 pregnant women: supplemental preformed vitamin A above 10,000 IU a day was linked to more cranial neural crest birth defects, about 1 in 57 exposed infants.
  5. Hansen JB, Berge LN, Svensson B, Lyngmo V, Nordøy A. Effects of cod liver oil on lipids and platelets in males and females. Eur J Clin Nutr. 1993;47(2):123-31..PubMedUsed to support: Controlled crossover study in 34 healthy non-smoking adults taking 25 mL a day of cod liver oil for 8 weeks: thromboxane B2 generation fell in both sexes; triglycerides fell 0.21 mmol/L and LDL rose 0.28 mmol/L in men only; HDL unchanged.
  6. Brox J, Olaussen K, Osterud B, Elvevoll EO, Bjørnstad E, Brattebøg G, Iversen H. A long-term seal- and cod-liver-oil supplementation in hypercholesterolemic subjects. Lipids. 2001;36(1):7-13. doi: 10.1007/s11745-001-0661-4.PubMedUsed to support: Randomized trial in 120 healthy adults with high cholesterol: 15 mL a day of seal oil or cod liver oil for 14 months lowered whole-blood platelet aggregation versus no supplement, with no change in cholesterol, HDL, post-meal triglycerides, apolipoproteins or lipoprotein(a).
  7. Egeland GM, Meyer HE, Selmer R, Tverdal A, Vollset SE. Cod liver oil consumption, smoking, and coronary heart disease mortality: three counties, Norway. Int J Circumpolar Health. 2001;60(2):143-9..PubMedUsed to support: Cohort of 42,612 Norwegian adults aged 35 to 54: reported cod liver oil use was not associated with coronary heart disease mortality (HR 1.0, 95% CI 0.8 to 1.3). Observational.
  8. Mavroeidi A, Aucott L, Black AJ, Fraser WD, Reid DM, Macdonald HM. Seasonal variation in 25(OH)D at Aberdeen (57°N) and bone health indicators--could holidays in the sun and cod liver oil supplements alleviate deficiency? PLoS One. 2013;8(1):e53381. doi: 10.1371/journal.pone.0053381.PubMedUsed to support: Longitudinal observational study of 365 postmenopausal women in Aberdeen: vitamin D deficiency was much less common in cod liver oil users (2.0% vs 23.7% in spring; 4.5% vs 24.8% in winter); seasonal vitamin D change had little effect on bone density.
  9. Eysteinsdottir T, Halldorsson TI, Thorsdottir I, Sigurdsson G, Sigurdsson S, Harris T, Launer LJ, Gudnason V, Gunnarsdottir I, Steingrimsdottir L. Cod liver oil consumption at different periods of life and bone mineral density in old age. Br J Nutr. 2015;114(2):248-56. doi: 10.1017/S0007114515001397.PubMedUsed to support: Observational study of 4,798 Icelanders aged 66 to 96: cod liver oil use in adolescence, midlife or old age was not associated with hip bone density, except a small difference in women taking it daily now; daily users had higher vitamin D levels.
  10. U.S. Department of Agriculture, Agricultural Research Service. Fish oil, cod liver (FDC ID 173577). USDA FoodData Central. 2019;SR Legacy food record 173577..SourceUsed to support: Not PubMed-indexed. Per 100 g: 30,000 mcg RAE vitamin A (100,000 IU), 250 mcg (10,000 IU) vitamin D, 6.9 g EPA and 11.0 g DHA; a teaspoon is 4.5 g, so about 1,350 mcg RAE (4,500 IU) vitamin A, 450 IU vitamin D and about 800 mg EPA plus DHA.
  11. Office of Dietary Supplements, National Institutes of Health. Vitamin A and Carotenoids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. 2025;Online fact sheet, updated March 10, 2025..SourceUsed to support: Not PubMed-indexed. Vitamin A is part of rhodopsin and supports the cornea; night blindness is the first sign of deficiency; chronic excess causes dry skin, joint pain, fatigue and abnormal liver tests; pregnant and breastfeeding women should not take more than 3,000 mcg RAE (10,000 IU) a day from supplements; retinoid medicines and orlistat interactions.
  12. Office of Dietary Supplements, National Institutes of Health. Vitamin D: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. 2025;Online fact sheet, updated June 27, 2025..SourceUsed to support: Not PubMed-indexed. Cod liver oil supplies 1,360 IU vitamin D per tablespoon; vitamin D promotes calcium absorption and bone mineralization; the UL ranges from 1,000 to 4,000 IU a day depending on age.
  13. Meyer HE, Smedshaug GB, Kvaavik E, Falch JA, Tverdal A, Pedersen JI. Can vitamin D supplementation reduce the risk of fracture in the elderly? A randomized controlled trial. J Bone Miner Res. 2002;17(4):709-15. doi: 10.1359/jbmr.2002.17.4.709.PubMedUsed to support: Double-blind randomized trial in 1,144 nursing home residents: 5 mL a day of ordinary cod liver oil (10 mcg vitamin D3) versus vitamin-D-free cod liver oil for 2 years raised blood vitamin D by 22 nmol/L but did not reduce hip or all nonvertebral fractures.