The Truth About Cod Liver Oil: Benefits, Side Effects & Why You Should Consider It.
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Cod liver oil has a long history of use as a nutritional supplement. It is derived from the liver of Atlantic cod (Gadus morhua) and has been taken across Northern Europe, particularly in Scandinavia and the UK, for well over a century. Its distinctive nutritional profile — rich in omega-3 fatty acids alongside the fat-soluble vitamins A and D — makes it different from standard fish oil supplements, which typically provide omega-3s alone.
This guide covers what cod liver oil is, how it differs from regular fish oil, what the constituent nutrients contribute to in the body, and what to look for when choosing a product.
What Is Cod Liver Oil and How Is It Different From Fish Oil?
Both cod liver oil and regular fish oil come from fish, but they are not the same product.
- Fish oil is extracted from the fatty tissue of oily fish such as salmon, mackerel, and sardines. It is primarily a source of the omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid).
- Cod liver oil comes specifically from the liver of cod fish. In addition to EPA and DHA, it contains meaningful amounts of vitamin A (retinol) and vitamin D — fat-soluble vitamins that are not present in meaningful quantities in standard fish oil.
This difference in nutrient profile is the main reason cod liver oil is considered separately from fish oil in nutritional contexts.
What Does Cod Liver Oil Contain?
The key nutritional components of cod liver oil and their EU-authorised roles in the body:
Omega-3 Fatty Acids (EPA and DHA)
- DHA contributes to the maintenance of normal brain function
- DHA and EPA contribute to the normal function of the heart
- DHA and EPA contribute to the maintenance of normal blood triglyceride levels
- DHA contributes to the maintenance of normal vision
Vitamin D
- Vitamin D contributes to the normal function of the immune system
- Vitamin D contributes to the maintenance of normal bones and muscle function
- Vitamin D contributes to normal blood calcium levels
Vitamin A
- Vitamin A contributes to the maintenance of normal vision
- Vitamin A contributes to the maintenance of normal skin
- Vitamin A contributes to the normal function of the immune system
Cod Liver Oil vs Regular Fish Oil
| Feature | Cod Liver Oil | Regular Fish Oil |
|---|---|---|
| Omega-3 (EPA & DHA) | ✅ Yes | ✅ Yes |
| Vitamin A | ✅ Yes | ❌ No |
| Vitamin D | ✅ Yes | ❌ No |
| Source | Cod liver | Fish fatty tissue |
Cod Liver Oil Side Effects and Cautions
Cod liver oil is widely used and generally well tolerated, but there are a few practical considerations:
- Vitamin A upper limits: Cod liver oil is one of the most concentrated dietary sources of vitamin A. Taking high doses over prolonged periods can lead to vitamin A accumulation. Pregnant women in particular should be cautious — excessive vitamin A is associated with risk to the developing baby. Always consult your GP or midwife during pregnancy.
- Digestive sensitivity: Some people experience mild nausea or digestive discomfort when first taking fish oil supplements, particularly on an empty stomach. Taking with food can help.
- Blood-thinning: Omega-3 fatty acids have a natural blood-thinning effect. If you are taking anticoagulant medication, consult your doctor before adding cod liver oil to your routine.
What to Look For in a Cod Liver Oil Supplement
- Cold-pressed or fermented: These processing methods better preserve heat-sensitive vitamins and fatty acids
- Third-party tested: Look for independent purity certification, particularly for heavy metals and oxidation levels
- Sustainable sourcing: MSC certification or equivalent is worth checking for ocean-caught products
- Check the vitamin A content: Given the upper limit considerations, knowing the vitamin A dose per serving matters
FAQs
What makes cod liver oil different from other fish oils?
Cod liver oil naturally contains significant amounts of vitamin A and D in addition to omega-3 fatty acids. Regular fish oil supplements typically provide omega-3s only, making cod liver oil a nutritionally distinct product.
How much cod liver oil should I take?
Always follow the dosage instructions on the product label. A typical adult dose is around 1–2 teaspoons (5–10 ml) of liquid or 1–2 capsules daily, but this varies by product strength. Consult a healthcare professional if you are unsure.
Is cod liver oil safe during pregnancy?
Cod liver oil is high in vitamin A, which should be monitored during pregnancy. It is best to consult your GP or midwife before using it during pregnancy or breastfeeding.
Is cod liver oil suitable for vegetarians?
No — cod liver oil is an animal-derived product. Those seeking plant-based omega-3 sources may prefer algae-based DHA/EPA supplements, which provide the active fatty acids without fish.
Fat-Soluble Vitamins and Antioxidants
Cod liver oil provides fat-soluble vitamins A and D — a category that also includes vitamin E, another important antioxidant nutrient. For a broader look at fat-soluble nutrients in whole foods, our guide to vitamin E in foods covers its role and how to obtain it from diet. For antioxidant-rich whole food supplements, browse our organic supplements range or our guide to antioxidant foods and ORAC values.
