Cod Liver Oil and Fish Oil Are Different Products With Overlapping Benefits

Cod liver oil and fish oil both contain omega-3 fatty acids, but they are not the same thing. Fish oil is made from the tissue of fatty fish like salmon, mackerel, and sardines. Cod liver oil comes specifically from the liver of Atlantic cod, and it contains not only omega-3s but also vitamins A and D. The omega-3 content is similar between the two, but the vitamin load is the main difference—and it matters if you already get enough vitamin A from food or supplements.

Both products work through the same basic mechanism: the omega-3 fatty acids EPA and DHA reduce inflammation in your bloodstream and tissues, support cell membrane function, and influence how your body regulates blood clotting and blood vessel function. The research on these effects is strongest for cardiovascular health, though studies have also examined their role in brain function, joint health, and immune response. What the evidence actually shows, and what remains uncertain, depends on which outcome you are looking at.

Key Takeaways

  • Fish oil and cod liver oil both contain omega-3 fatty acids EPA and DHA, which reduce inflammation and support heart and brain function, but cod liver oil also contains vitamins A and D.
  • The strongest evidence supports fish oil for lowering triglycerides and supporting heart health in people with existing cardiovascular disease, based on multiple human trials.
  • Evidence for brain health, joint pain, and immune function is emerging but not yet conclusive—most studies are small or conducted in animals.
  • Cod liver oil's added vitamins A and D can be beneficial, but taking too much vitamin A over time may increase certain health risks, so the dose matters.
  • Fish oil can thin blood slightly and may interact with blood thinners or high-dose aspirin, so tell your doctor if you take either regularly.

How Omega-3 Fatty Acids Affect Heart Health and Blood Lipids

The most robust evidence for fish oil comes from studies on triglycerides and heart disease. Triglycerides are a type of fat in your blood; high levels are linked to increased cardiovascular risk. Multiple randomized controlled trials—the gold standard in human research—have shown that fish oil supplements lower triglycerides by 20 to 30 percent in people with elevated levels. The effect is dose-dependent: higher doses produce larger reductions.

The evidence for preventing heart attacks or strokes in people without existing heart disease is weaker. Large observational studies (which track people over time but cannot prove cause and effect) suggest that eating fatty fish regularly is associated with lower heart disease risk, but randomized trials of fish oil supplements in healthy people have not consistently shown the same benefit. The VITAL trial, a major 2022 study of over 25,000 people, found that fish oil did not reduce heart attack or stroke risk in people without prior cardiovascular disease. However, in people who already have heart disease or high triglycerides, the evidence for benefit is clearer.

Brain Function and Cognitive Decline: What the Research Shows

EPA and DHA are structural components of brain cell membranes, which is why they are often marketed for memory and cognitive health. Animal studies consistently show that omega-3 deficiency impairs learning and memory, and that supplementation can reverse some of these effects. In humans, observational data links higher fish consumption to better cognitive outcomes in older adults, and some small trials suggest fish oil may slow cognitive decline in people with mild memory problems.

The evidence is not yet strong enough to recommend fish oil specifically for preventing dementia or age-related cognitive decline in healthy people. Most human trials have been small, conducted over short periods, or included people already showing cognitive symptoms. Larger, longer trials are underway. If you are interested in brain health, the current evidence supports eating fatty fish two to three times per week as part of a broader diet pattern—the Mediterranean diet, which emphasizes fish, has the strongest evidence for cognitive protection.

Joint Pain, Inflammation, and Emerging Research

Fish oil's anti-inflammatory properties have led to investigation in rheumatoid arthritis and other inflammatory joint conditions. Several randomized trials have found that fish oil supplements reduce joint pain and swelling in people with rheumatoid arthritis, and some studies suggest it may work better when combined with standard medications. The effect sizes are modest—improvements in pain and function are real but not dramatic—and not all trials show benefit.

For osteoarthritis and general joint pain in otherwise healthy people, the evidence is much thinner. Most studies are small or conducted in animals. Fish oil is not a replacement for physical therapy, weight management, or prescribed treatments, but it may be a reasonable addition if you have inflammatory arthritis and want to explore options beyond medication alone. Talk with your rheumatologist about whether it makes sense for your specific condition.

Cod Liver Oil's Added Vitamins: Benefits and Risks

Cod liver oil contains 4,000 to 10,000 IU of vitamin A and 400 to 1,000 IU of vitamin D per standard dose, depending on the product. Vitamin D supports bone health and immune function, and many people do not get enough from food and sunlight alone. Vitamin A is essential for vision and immune function. If your diet is low in these vitamins, cod liver oil can help you reach adequate intake.

The catch is that vitamin A is fat-soluble, meaning your body stores excess amounts in liver tissue. Taking too much vitamin A over months or years can accumulate to toxic levels, causing headaches, nausea, bone pain, and in severe cases, liver damage. The upper safe limit for adults is 10,000 IU per day from supplements. If you already take a multivitamin, eat vitamin A-rich foods like sweet potato or leafy greens regularly, or take a separate vitamin A supplement, cod liver oil could push you over that limit. Fish oil, which lacks these vitamins, avoids this concern entirely.

Potential Side Effects and Drug Interactions

Fish oil and cod liver oil are generally well tolerated, but they do have known effects. The most common side effect is a fishy aftertaste or mild digestive upset, which often improves if you take the supplement with food or switch to an enteric-coated product (designed to dissolve in the intestine rather than the stomach). Some people report loose stools or nausea at higher doses.

Fish oil has a mild blood-thinning effect because omega-3s reduce platelet aggregation. This is usually not a problem, but if you take prescription blood thinners like warfarin or apixaban, or if you take high-dose aspirin regularly, you should tell your doctor before starting fish oil. The combination is not necessarily dangerous, but your doctor may want to monitor you or adjust doses. If you are having surgery, mention fish oil use to your surgical team, as some recommend stopping it a week or two beforehand.

Choosing Between Fish Oil and Cod Liver Oil

The choice depends on your diet and health goals. If you want omega-3s for heart or brain health and you already get adequate vitamin A and D from food or a multivitamin, fish oil is the simpler choice—you avoid the risk of excess vitamin A. If your vitamin D is low (which is common, especially in winter or at northern latitudes) and you do not take a separate supplement, cod liver oil can address both needs in one product.

Check the label for the amount of EPA and DHA per dose. Most research on triglyceride reduction used doses of 2 to 4 grams of combined EPA and DHA per day. For general health, 1 to 2 grams per day is a common dose, though there is no single "correct" amount. Look for products that have been third-party tested for purity and potency—organizations like NSF International or USP verify that supplements contain what the label says and are free of contaminants like mercury.

Frequently Asked Questions

Can I get the same benefits from eating fish instead of taking a supplement?

Yes, if you eat fatty fish regularly. Two to three servings per week of salmon, mackerel, sardines, or herring provides 2 to 3 grams of omega-3s and avoids the question of supplement quality. Supplements are useful if you do not eat fish, are allergic to it, or need a higher dose for a specific condition like high triglycerides. Food is always the first choice.

Is fish oil safe to take long-term?

Fish oil is safe for most people at standard doses (1 to 3 grams per day) over years. The main concern is if you take blood thinners or high-dose aspirin, in which case you should check with your doctor. Cod liver oil is safe long-term as long as you stay below 10,000 IU of vitamin A per day from all sources combined.

Will fish oil help my cholesterol?

Fish oil lowers triglycerides reliably, but it does not significantly lower LDL cholesterol (the "bad" kind) and may slightly raise it in some people. It may raise HDL cholesterol (the "good" kind) modestly. If your main concern is LDL, statins are far more effective. Fish oil is useful if your triglycerides are high or if you have heart disease and want additional support alongside other treatments.

What is the difference between fish oil and krill oil?

Krill oil comes from tiny shrimp-like crustaceans and contains omega-3s in a different chemical form (phospholipids rather than triglycerides). Marketing claims that this form is better absorbed, but human evidence does not support superior benefits compared to fish oil. Krill oil is more expensive and offers no clear advantage for most people.

Can I take fish oil if I am pregnant or nursing?

Fish oil is generally considered safe in pregnancy and nursing at standard doses, and DHA is important for fetal brain development. However, cod liver oil should be avoided in pregnancy because high vitamin A intake in the first trimester is linked to birth defects. Pregnant people should talk with their obstetrician about whether fish oil makes sense for their situation.