Omega-3 Fatty Acids in Cod Liver Oil: UK Guide

Omega-3 fatty acids from cod liver oil have been a cornerstone of British nutritional health for generations, valued for their role in supporting heart, joint, and brain function. Cod liver oil is extracted from Atlantic cod livers and provides EPA and DHA alongside naturally occurring vitamins A and D, giving it a broader nutritional profile than many standard fish oil supplements. This article explains how cod liver oil delivers omega-3 fatty acids, what the evidence says about its health benefits, how much to take safely, who should avoid it, and how it compares to other omega-3 supplements available in the UK.

What are omega-3 fatty acids and how does cod liver oil provide them?

Cod liver oil supplies EPA and DHA, the long-chain omega-3 fatty acids most readily used by the body, alongside vitamins A and D extracted from Atlantic cod livers. The body converts plant-based ALA to EPA and DHA only inefficiently, making marine sources such as cod liver oil more reliable.

Omega-3 fatty acids are a family of polyunsaturated fats that the human body cannot synthesise in adequate amounts and must therefore obtain from food or supplements. The three most nutritionally significant forms are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is found mainly in plant sources such as flaxseed and walnuts, while EPA and DHA are found predominantly in marine sources and are the forms most readily used by the body.

Cod liver oil is extracted from the livers of Atlantic cod and provides EPA and DHA alongside naturally occurring vitamins A and D, making its nutritional profile broader than that of many standard fish body oils. Unlike fish body oils pressed from the flesh of oily fish, cod liver oil is not typically the most concentrated source of EPA and DHA per capsule; many fish body oil concentrates provide higher amounts of these fatty acids per serving. The combination of omega-3 fatty acids and vitamins A and D has made cod liver oil a familiar supplement in British households, particularly for supporting general health during winter months when sunlight exposure is limited. Because cod liver oil contains vitamin A, dosing considerations apply to all age groups, including children.

The EPA and DHA in cod liver oil are incorporated into cell membranes throughout the body, where they influence membrane fluidity and function. They also serve as precursors to signalling molecules called eicosanoids, which play roles in regulating inflammation, blood clotting, and immune responses. Because the body converts ALA to EPA and DHA only inefficiently, marine-derived sources such as cod liver oil are considered a more reliable way to maintain adequate tissue levels of these long-chain omega-3 fatty acids, as noted by the Scientific Advisory Committee on Nutrition (SACN).^[15][16]

What are the health benefits of taking cod liver oil regularly?

EPA and DHA at 250 mg per day support normal heart function and DHA supports normal brain function and vision, as confirmed by authorised health claims. Omega-3 fatty acids may also reduce joint pain and morning stiffness in rheumatoid arthritis, though they are adjunctive to prescribed treatment.

Regular use of cod liver oil is associated with several evidence-supported health benefits, particularly relating to cardiovascular health, joint function, and bone health.

The Great Britain Nutrition and Health Claims Register (based on authorised EFSA opinions) confirms that EPA and DHA contribute to the normal function of the heart at an intake of at least 250 mg per day of combined EPA and DHA. DHA at the same intake level supports maintenance of normal brain function and normal vision. These claims are relevant at the doses provided by most standard cod liver oil products. Separate authorised claims relating to the maintenance of normal blood pressure and normal blood triglyceride concentrations require substantially higher intakes (approximately 3 g per day of EPA and DHA for blood pressure, and at least 2 g per day for triglycerides). These higher doses are not typically achieved through standard cod liver oil supplementation and usually involve pharmaceutical-grade omega-3 preparations used under medical supervision. It would therefore be misleading to suggest that cod liver oil at standard doses supports blood pressure or triglyceride reduction.

For joint health, omega-3 fatty acids have anti-inflammatory properties that may help reduce morning stiffness and joint tenderness in people with rheumatoid arthritis. A Cochrane review of marine omega-3 supplementation in rheumatoid arthritis found a modest reduction in joint pain and morning stiffness compared with placebo. NICE guideline NG100 on the management of rheumatoid arthritis in adults positions lifestyle factors, including diet, as supportive measures alongside disease-modifying antirheumatic drug (DMARD) therapy.^[9][10] Omega-3 supplementation should be considered adjunctive only and must not replace prescribed treatment.

The vitamin D content of cod liver oil is clinically relevant in the UK, where the NHS advises that adults consider a daily vitamin D supplement of 10 micrograms, especially during autumn and winter. Cod liver oil can contribute meaningfully to this intake. The vitamin A content supports immune function and skin health, though this also introduces important dosing considerations discussed in later sections.

There is emerging evidence that DHA, as a major structural component of brain tissue, may support mental wellbeing, but the evidence base for specific mental health conditions remains mixed. Cod liver oil should not be presented as a treatment for any psychiatric diagnosis.

How much cod liver oil should I take each day?

Most standard UK cod liver oil products provide 250 to 500 mg of combined EPA and DHA per serving; follow the manufacturer's dose to stay within safe vitamin A limits. Higher doses for conditions such as hypertriglyceridaemia require pharmaceutical-grade preparations under medical supervision.

The appropriate daily amount of cod liver oil depends on the product's concentration of EPA, DHA, vitamin A, and vitamin D, so reading the product label carefully is essential before establishing a routine dose. Most standard UK cod liver oil capsules or liquids provide between 250 mg and 500 mg of combined EPA and DHA per serving, and manufacturers' recommended doses are typically designed to stay within safe upper limits for vitamin A.

The NHS advises that most people can meet their omega-3 needs by eating two portions of fish per week, one of which should be oily fish such as salmon, mackerel, or sardines.^[1][18] For those who do not eat fish, a supplement providing at least 250 mg of combined EPA and DHA daily is consistent with the intake level at which the heart function health claim is authorised under the GB Nutrition and Health Claims Register. Higher doses are sometimes used under medical supervision for specific conditions such as hypertriglyceridaemia, but these typically involve pharmaceutical-grade omega-3 preparations rather than standard cod liver oil.

Because cod liver oil contains vitamin A as well as omega-3 fatty acids, it is important not to exceed the manufacturer's stated dose. The NHS advises that taking more than 1.5 mg (1,500 micrograms) of vitamin A per day from all sources over a long period may be harmful. People who eat liver or liver products (such as pâté) once a week or more should not take cod liver oil or other vitamin A-containing supplements, as their dietary intake may already be close to or above the upper level. Most standard cod liver oil products are formulated to remain within safe limits at the recommended dose, but combining multiple supplements containing vitamin A can lead to unintentional excess. Always check the total vitamin A content across all supplements being taken simultaneously.

Are there any side effects or risks I should know about?

Cod liver oil is generally well tolerated but can cause fishy aftertaste, nausea, or loose stools, especially on an empty stomach. Excess vitamin A over time risks toxicity, and those on anticoagulants should seek advice before use.

Cod liver oil is generally well tolerated at recommended doses, but some people experience mild gastrointestinal side effects, particularly when starting supplementation. These can include:

• A fishy aftertaste or fishy-smelling breath

• Nausea or stomach discomfort, especially if taken on an empty stomach

• Loose stools or mild diarrhoea at higher doses

Taking cod liver oil with food, or choosing an enteric-coated capsule formulation, can help reduce these effects for most people.

At high doses, omega-3 fatty acids can have a mild anticoagulant effect, meaning they may slightly prolong bleeding time.^[17] This is unlikely to be clinically significant at standard supplement doses, but it is worth noting for anyone taking anticoagulant medicines such as warfarin or direct oral anticoagulants (DOACs). Anyone on such medicines should speak to their GP or pharmacist before starting cod liver oil; the BNF and Specialist Pharmacy Service (SPS) provide guidance for healthcare professionals on this interaction.

Excessive intake of vitamin A, which is present in cod liver oil, carries a risk of toxicity over time. Symptoms of chronic vitamin A excess can include headache, dry skin, liver changes, and bone pain, as described in NHS guidance on vitamin A.^[2][6] This risk is most relevant to people who are already consuming other vitamin A-containing supplements or eating large amounts of liver.

If you experience an unexpected or severe reaction after taking cod liver oil and you believe it may be related to a medicine, vaccine, or herbal product you are also taking, you or your healthcare professional can report it to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk. For concerns about the supplement itself as a food product, contact the manufacturer or seek advice from your GP or local Trading Standards service.

Who should avoid cod liver oil or speak to a GP first?

Pregnant women must avoid cod liver oil because its high vitamin A content is teratogenic. People on anticoagulants, those with liver disease, fish allergy, or high existing vitamin A intake should consult a GP or pharmacist first.

Certain groups should exercise caution with cod liver oil or seek medical advice before taking it. The most important group is pregnant women. The NHS advises that pregnant women should avoid cod liver oil supplements because the high vitamin A content may be harmful to the developing baby.^[5] Vitamin A in excess is teratogenic, meaning it can cause birth defects, and the NHS specifically recommends that pregnant women do not take supplements containing vitamin A, including cod liver oil.^[13][14] Women who are planning a pregnancy should also discuss this with their GP or midwife.

People who are breastfeeding should also seek advice before taking cod liver oil, as vitamin A passes into breast milk and excessive intake could affect the infant. Women of childbearing potential who are not using reliable contraception should be aware of this risk.

Other groups who should speak to a GP or pharmacist before starting cod liver oil include:

• People taking anticoagulant medicines such as warfarin, heparin, or DOACs, due to the potential for omega-3 fatty acids to affect bleeding

• People with a fish allergy, as cod liver oil is derived from fish; those with a shellfish allergy do not necessarily need to avoid cod liver oil, but should check product labels for any cross-contamination warnings

• People with liver disease, as vitamin A is metabolised by the liver and may accumulate

• People already taking high-dose vitamin A or multivitamins containing vitamin A

• Children, for whom age-appropriate formulations and doses should be used, and for whom a GP or pharmacist can advise on suitability

If you are unsure whether cod liver oil is appropriate for your circumstances, your GP or community pharmacist is the right first point of contact.

How does cod liver oil compare to other omega-3 supplements?

Fish body oils provide higher EPA and DHA concentrations without vitamin A, making them preferable for those wanting higher omega-3 doses. Algae-based supplements suit vegetarians and vegans, while flaxseed oil offers only ALA, which converts poorly to the long-chain forms.

Cod liver oil is one of several omega-3 supplement options available in the UK, and understanding the differences helps in choosing the most appropriate product for individual needs. The main alternatives include fish oil (derived from the body of oily fish rather than the liver), algae-based omega-3 supplements, and flaxseed oil.

Fish body oils, such as those derived from salmon, mackerel, or anchovies, typically provide higher concentrations of EPA and DHA per capsule than cod liver oil, without the added vitamins A and D. This makes fish body oil a more suitable choice for people who want a higher omega-3 dose without the risk of excess vitamin A, or for those who are already taking a separate vitamin D supplement.

Algae-based omega-3 supplements are derived from the microalgae that fish themselves consume, making them a suitable option for vegetarians and vegans. They provide DHA and, in some formulations, EPA, without any animal-derived ingredients. The NHS recognises algae-based supplements as an alternative source of omega-3 for those who do not eat fish.^[12]

Flaxseed oil provides ALA, the plant-based omega-3, but the body's conversion of ALA to EPA and DHA is limited and variable, making it a less reliable source of the long-chain forms most associated with cardiovascular and brain health.

Cod liver oil remains a practical and cost-effective choice for people who want a combined source of omega-3 fatty acids alongside vitamins A and D, provided they stay within recommended doses. For those seeking higher omega-3 intakes or who have specific health conditions, a healthcare professional can advise on whether a more concentrated or specialised formulation is more appropriate. Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online health consultations, with prescriber review and pharmacist support, where clinically appropriate options can be discussed.

Scientific References

1. Fish and shellfish.
2. Vitamin A – Vitamins and minerals.
3. Vitamin D – Vitamins and minerals.
4. Vitamin D deficiency: migrant health guide.
5. Pregnancy vitamins and supplements.
6. Lay summary of the statement on the effects of excess vitamin A on maternal health.
7. Great Britain nutrition and health claims (NHC) register.
8. Scientific Opinion on the substantiation of a health claim relating to DHA and maintenance of normal brain function.
9. Rheumatoid arthritis in adults: management (NG100).
10. Rheumatoid arthritis in adults: management (NG100) – Recommendations chapter.
11. Rheumatoid arthritis – Treatment.
12. The vegan diet.
13. Teratogenicity of High Vitamin A Intake.
14. Vitamin A-Mediated Birth Defects: A Narrative Review.
15. Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)? Gerster H. Int J Vitam Nutr Res. 1998..
16. Effects of Dietary α-Linolenic Acid Treatment and the Efficiency of Its Conversion to Eicosapentaenoic and Docosahexaenoic Acids in Obesity and Related Diseases.
17. The Use of Fish Oil with Warfarin Does Not Significantly Affect either the International Normalised Ratio or Incidence of Adverse Events in Patients with Atrial Fibrillation and Deep Vein Thrombosis: A Retrospective Study.
18. Omega-3 – British Dietetic Association.

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