Cod liver oil is a nutrient-rich supplement extracted from the livers of cod fish, used primarily to supply omega-3 fatty acids along with vitamins A and D. That combination in a single supplement is what sets it apart from regular fish oil and explains its wide range of uses, from supporting joint health and bone strength to protecting vision and heart function.
What’s Actually in Cod Liver Oil
One teaspoon of cod liver oil provides about 310 mg of EPA and 495 mg of DHA, the two omega-3 fatty acids most closely tied to health benefits. But the real distinguishing feature is the vitamin content: a single tablespoon delivers roughly 4,080 micrograms of vitamin A and 1,360 IU of vitamin D. Regular fish oil, by comparison, contains neither vitamin.
This combination is both a strength and a limitation. Because it delivers several active nutrients at once, cod liver oil isn’t ideal for targeting a single deficiency. If you specifically need high-dose omega-3s, a concentrated fish oil product will give you more EPA and DHA per capsule. If you need vitamin D alone, a standalone supplement lets you control the dose without also loading up on vitamin A. Cod liver oil works best as a broad-spectrum daily supplement for people who want modest amounts of all three nutrients in one dose.
Joint Pain and Arthritis
One of the oldest and most studied uses for cod liver oil is managing symptoms of rheumatoid arthritis. In clinical research, patients taking cod liver oil experienced a 52% reduction in morning stiffness, a 43% decrease in painful joints, and a 40% drop in swollen joints. Pain intensity fell by nearly 68%. These effects come from the anti-inflammatory properties of EPA and DHA, which help dial down the immune responses that drive joint swelling and stiffness.
The vitamin D in cod liver oil may also play a supporting role here, since low vitamin D levels are common in people with inflammatory joint conditions and can worsen symptoms.
Bone Health and Rickets Prevention
Cod liver oil was the original weapon against rickets, the childhood bone disease caused by vitamin D deficiency. By the 1930s, researchers had identified the oil’s anti-rachitic (bone-strengthening) properties clearly enough to make it a standard pediatric supplement. That widespread use effectively eradicated rickets in the United States.
The principle still applies today. Vitamin D helps your body absorb calcium and deposit it into bone tissue. For people who get limited sun exposure or don’t consume much dairy, cod liver oil offers a food-based source of vitamin D that supports bone mineral density across all ages.
Heart and Cholesterol Support
The omega-3 fatty acids in cod liver oil have a measurable effect on blood fats. In studies on people with mild to moderate high blood pressure, fish oil supplementation reduced serum triglyceride levels by 30%. Triglycerides are the fat molecules most directly linked to cardiovascular risk when elevated, and bringing them down is one of the best-documented benefits of EPA and DHA.
The effect on blood pressure itself is more modest. Clinical trials have generally found only small, sometimes insignificant reductions in blood pressure from fish oil alone. So if triglycerides are your primary concern, cod liver oil can help meaningfully. For blood pressure, it’s unlikely to replace other interventions.
Vision and Eye Health
DHA makes up 50% to 60% of the total fatty acid content in the outer segments of your retinal photoreceptors, the cells that detect light. These cells constantly shed and rebuild their outer membranes, which means they need a continuous dietary supply of DHA to function properly. A shortage may increase the risk of age-related macular degeneration, the leading cause of vision loss in older adults.
Beyond simply providing structural material, the omega-3s in cod liver oil appear to reduce inflammation and suppress the growth of abnormal blood vessels in the retina, two processes central to macular degeneration progression. The vitamin A content adds another layer of protection, since vitamin A is essential for producing the pigments your retina uses to process light. Severe vitamin A deficiency causes night blindness, and even mild insufficiency can impair visual function over time.
Mood and Brain Function
Omega-3 fatty acids have been linked to reduced symptoms of mood disorders, and animal research has begun to clarify why. In studies using rat models of depression, cod liver oil treatment increased the number of neurons in the hippocampus and frontal cortex, brain areas critical for mood regulation and memory. The oil also boosted antioxidant levels in brain tissue while reducing oxidative damage, a pattern that mirrors the effects of conventional antidepressant medication.
These findings are from animal studies, so they don’t translate directly to human treatment recommendations. But they align with broader population research showing that people who consume more omega-3s tend to report fewer depressive symptoms. The combination of EPA, DHA, and the antioxidant vitamins A and D may work together to protect brain cells from the kind of stress-related damage associated with depression and cognitive decline.
Cod Liver Oil vs. Fish Oil
The two supplements come from different parts of the fish and serve slightly different purposes. Fish oil is extracted from the body of fatty fish like mackerel, sardines, or anchovies. A typical 1,000 mg fish oil capsule contains about 180 mg of EPA and 120 mg of DHA, with no vitamins A or D.
Cod liver oil comes specifically from the liver of cod, where fat-soluble vitamins concentrate. It delivers less omega-3 per milligram of oil but adds substantial amounts of vitamins A and D. If your goal is maximizing omega-3 intake for heart health, fish oil is the more efficient choice. If you want a broader nutritional supplement that also covers vitamin A and D needs, cod liver oil fills more gaps at once.
Safety and Vitamin A Limits
The main safety concern with cod liver oil is vitamin A. Because the oil is so rich in it, taking more than the recommended dose can push you past safe limits. The European Food Safety Authority sets the tolerable upper intake for vitamin A at 3,000 micrograms per day for women of childbearing age, based on the risk of liver damage and harm to a developing fetus. A single tablespoon of cod liver oil contains over 4,000 micrograms, which already exceeds that ceiling.
This is why most people take cod liver oil by the teaspoon rather than the tablespoon, or use capsules with controlled doses. Pregnant women should avoid cod liver oil entirely because of the risk of birth defects from excess vitamin A. The UK Expert Committee on Vitamins and Minerals has flagged intakes above 1,500 micrograms per day as potentially harmful to bone health, which means even moderate supplementation requires attention to what else in your diet contains vitamin A.
Mercury and Contaminants
Concerns about mercury in fish products are reasonable, but cod liver oil supplements consistently test well below safety limits. In laboratory analyses of commercial products, the average mercury concentration in cod liver oil was 0.106 micrograms per kilogram, far below the 100 microgram per kilogram maximum allowed in dietary supplements. None of the tested products came close to exceeding that standard. Interestingly, vegetable oil supplements in the same study contained roughly twice as much mercury on average as cod liver oil.
Storage and Freshness
Omega-3 fatty acids are vulnerable to oxidation, which breaks them down and produces a rancid taste and smell. Oxidized oil doesn’t just taste bad; it loses the essential fatty acids that make it beneficial. To keep cod liver oil fresh, store it at cool temperatures and away from light. Liquid forms in dark glass bottles should be refrigerated after opening.
Capsules tend to stay fresh longer because the encapsulating material acts as a barrier against oxygen and light. In sensory evaluations of commercial omega-3 products, capsulated samples showed no detectable rancid odor or flavor even after extended storage at room temperature. If your liquid cod liver oil smells sharp or fishy beyond its normal mild scent, it has likely oxidized and should be replaced.