Cod liver oil is a genuinely beneficial supplement for most people, primarily because it delivers three nutrients in one dose: omega-3 fatty acids (EPA and DHA), vitamin A, and vitamin D3. That combination sets it apart from regular fish oil and makes it useful for heart health, immune function, and vision. But it also comes with a real risk of getting too much vitamin A, which makes dosing more important than with other fish oil supplements.
What Makes It Different From Fish Oil
Regular fish oil comes from the body flesh of fatty fish like salmon, mackerel, and anchovies. Cod liver oil comes specifically from the liver of cod. Both provide omega-3 fatty acids, but cod liver oil also contains significant amounts of vitamins A and D3, which regular fish oil does not. This is both its main advantage and its main limitation.
If you already get plenty of vitamin A and D from your diet or a multivitamin, cod liver oil could push you past safe levels, particularly for vitamin A. If you’re low in those vitamins, especially vitamin D during winter months, cod liver oil pulls double duty in a way regular fish oil can’t.
Heart and Triglyceride Benefits
The omega-3s in cod liver oil have well-documented effects on blood fats. At therapeutic doses (around 4 grams per day of EPA and DHA combined), omega-3 fatty acids reduce triglycerides by roughly 27%, with a range of 21% to 35% depending on the study. For people already taking a statin, the reduction is closer to 21%. One trial in people with very low baseline omega-3 levels saw triglycerides drop by 48%.
A standard tablespoon of cod liver oil doesn’t deliver 4 grams of EPA and DHA, so the triglyceride-lowering effect at typical doses will be more modest. Still, consistent daily intake contributes to a healthier lipid profile over time. One thing to be aware of: supplements containing both EPA and DHA can raise LDL cholesterol slightly, while EPA-only formulations tend not to. Cod liver oil contains both.
Vitamin D and Immune Function
Vitamin D3 is one of the strongest reasons to choose cod liver oil over regular fish oil. Many people, particularly those living in northern latitudes or spending most of their time indoors, run low on vitamin D. A daily serving of cod liver oil provides a meaningful dose without needing a separate supplement. Vitamin D supports immune function, calcium absorption, and bone maintenance, making cod liver oil especially practical during the darker months of the year.
Vision and Eye Health
The combination of vitamin A and omega-3s in cod liver oil may support eye health on multiple fronts. Vitamin A is essential for maintaining healthy vision, particularly in low light. The omega-3 fatty acids EPA and DHA appear to help regulate pressure inside the eye and protect retinal neurons from oxidative stress. Research has suggested that this combination could be beneficial for people at risk of glaucoma, since these fatty acids also support blood flow to the optic nerve. That said, cod liver oil alone is not a treatment for established eye disease.
Effects on Mood and Depression
Countries where people eat large amounts of fish tend to have lower rates of depression, which sparked decades of research into omega-3s and mental health. More than 30 clinical trials have tested omega-3 preparations in people with depression, and the pooled results generally favor omega-3s over placebo, though findings aren’t unanimous due to differences in dosing and formulations across studies.
The preparations that work best for mood appear to contain at least 60% EPA relative to DHA, at doses between 1 and 2 grams per day. Cod liver oil contains both EPA and DHA, though the ratio varies by brand. If you’re specifically interested in omega-3s for mood support, check the label to see whether the EPA content is high enough relative to DHA.
Joint Pain: Limited Evidence
Despite its reputation as a joint supplement, the clinical evidence for cod liver oil specifically reducing joint pain is thin. In one 24-week trial, 86 patients with osteoarthritis took either 10 ml of cod liver oil or an olive oil placebo daily alongside their regular pain medication. There was no significant benefit for the cod liver oil group compared to placebo. Omega-3s do have anti-inflammatory properties, but at the doses found in a typical serving of cod liver oil, the effect on joint stiffness and pain may not be large enough to notice.
The Vitamin A Risk
This is the single most important thing to understand about cod liver oil. The tolerable upper intake level for vitamin A in adults is 3,000 mcg (10,000 IU) per day. Going above that consistently causes chronic toxicity, which can show up as severe headaches, hair loss, dry and itchy skin, cracked lips, weakness, and even liver enlargement. These symptoms develop gradually and are easy to mistake for other conditions.
A tablespoon of cod liver oil can contain a substantial portion of that upper limit. If you’re also eating foods rich in vitamin A (liver, fortified cereals, dairy) or taking a multivitamin that includes it, you could exceed safe levels without realizing it. Children are especially vulnerable to vitamin A toxicity, which can cause joint pain, appetite loss, and growth problems. Always check the vitamin A content on the label before giving cod liver oil to kids, and keep the dose conservative.
Pregnancy: A Clear Warning
Pregnant women and women trying to conceive should avoid cod liver oil unless specifically directed otherwise by a doctor. The UK government explicitly advises against liver products and fish liver oil supplements during pregnancy because excess vitamin A can cause serious birth defects, including abnormal development of the spine, heart, kidneys, and limbs. This is not a “just to be safe” precaution. The risk of fetal malformations from high vitamin A intake is well established. Regular fish oil, which provides omega-3s without the vitamin A, is a safer alternative during pregnancy.
Dosage and How to Take It
Most adults use 15 to 20 ml (roughly one tablespoon) of liquid cod liver oil per day. Capsule doses vary by brand, so read the label for the EPA, DHA, vitamin A, and vitamin D content per serving. Taking it with a meal that contains some fat improves absorption, since all of the key nutrients in cod liver oil are fat-soluble.
Before starting, add up your total vitamin A intake from all sources: food, multivitamins, and the cod liver oil itself. If the combined total stays well below 10,000 IU per day, you’re in safe territory. If you’re already taking a multivitamin with vitamin A, switching to regular fish oil and a separate vitamin D supplement may be a smarter approach than stacking cod liver oil on top.
Contaminant Levels
Because cod liver oil comes from the liver, an organ that filters toxins, contamination is a reasonable concern. Testing of commercially available cod liver oil capsules has found total mercury levels ranging from 0.013 to 2.03 nanograms per gram, with the best products at the low end of that range. Reputable brands test for mercury, PCBs, and other contaminants and publish those results. If a brand doesn’t make purity testing available, that’s a reason to choose one that does.