Cod liver oil delivers a combination of nutrients you won’t find in most other supplements: omega-3 fatty acids, vitamin A, and vitamin D, all in a single dose. That trio is what sets it apart from regular fish oil and gives it a uniquely broad range of health benefits, from joint pain relief to better eye health. A single tablespoon contains about 1,360 IU of vitamin D and 13,600 IU of vitamin A, along with a concentrated dose of the same omega-3s found in fatty fish.
How It Differs From Regular Fish Oil
Standard fish oil comes from the flesh of fatty fish like salmon, mackerel, and anchovies. Cod liver oil comes specifically from the livers of Atlantic or Pacific cod. Both are rich in omega-3 fatty acids (EPA and DHA), but the liver source adds significant amounts of vitamins A and D that regular fish oil simply doesn’t provide. About 30% of fish oil is pure omega-3s, but cod liver oil layers those fat-soluble vitamins on top.
If your main goal is omega-3 intake, either product works. If you also want vitamins A and D without taking separate supplements, cod liver oil covers all three in one dose.
Joint Pain and Stiffness
One of the most well-supported benefits of cod liver oil is its effect on joint inflammation, particularly in rheumatoid arthritis. A clinical study found that people with rheumatoid arthritis who supplemented with cod liver oil experienced a 52% reduction in morning stiffness. The omega-3 fatty acids EPA and DHA are responsible for most of this effect. They work by dialing down the production of inflammatory compounds in the body, which reduces swelling and pain in the joints. Some participants in arthritis studies have also been able to cut back on anti-inflammatory painkillers after consistent supplementation.
Heart and Blood Vessel Health
The omega-3s in cod liver oil have a meaningful effect on triglycerides, a type of blood fat linked to heart disease when levels run high. At therapeutic doses, omega-3 fatty acids can lower triglyceride levels by 20% to 30%. The American Heart Association has noted that EPA, one of the two main omega-3s in cod liver oil, combined with cholesterol-lowering medication led to a 25% reduction in heart attack, stroke, and cardiovascular death among people with elevated triglycerides.
It’s worth noting that these larger reductions were seen at prescription-strength doses (4 grams per day of omega-3s), which is far more than a standard serving of cod liver oil provides. A daily teaspoon or tablespoon still contributes to your overall omega-3 intake, but it won’t match the triglyceride-lowering power of high-dose prescriptions on its own.
Eye and Vision Protection
Cod liver oil supports eye health through two different mechanisms working together. Vitamin A is essential for the surface of the eye, helping maintain the cornea and the thin membrane that lines the eyelids. It also plays a central role in how your retina converts light into the signals your brain interprets as vision. Without adequate vitamin A, night vision deteriorates first, followed by more serious damage over time.
The omega-3 component adds a second layer of protection. These fatty acids help maintain blood flow to the eye and support the health of the optic nerve. Research published in the National Library of Medicine has proposed that the combination of vitamin A and omega-3s in cod liver oil could be particularly beneficial for people at risk of glaucoma, because omega-3s help lower pressure inside the eye while vitamin A acts as an antioxidant, protecting delicate eye tissues from oxidative damage.
Vitamin D and Bone Health
Cod liver oil has been used as a vitamin D source for generations, especially in northern countries where sunlight is scarce for months at a time. In Iceland, which sits between 62 and 67 degrees north latitude, cod liver oil was given to schoolchildren throughout the mid-20th century because the skin produces little to no vitamin D from roughly October through April. It remains a recommended supplement there for people of all ages.
Vitamin D is critical for calcium absorption, and severe deficiency causes rickets in children and soft, weakened bones in adults. As a prevention tool for deficiency, cod liver oil is effective. However, its direct impact on bone density in later life appears modest. A large Icelandic study tracking cod liver oil use across different life stages found no strong link between past intake and hip bone density in old age. Women who took it daily did show slightly higher bone density scores than those who rarely used it, but the difference was small. The takeaway: cod liver oil reliably prevents vitamin D deficiency, which is foundational for bone health, but it’s not a standalone solution for building stronger bones.
Mood and Brain Function
Populations that eat diets rich in omega-3 fatty acids consistently show lower rates of major depression and prenatal depression. The connection appears to involve DHA, which is a structural component of brain cell membranes. Higher DHA levels in the brain are associated with increased growth of new brain cells in the hippocampus, the region responsible for learning and memory.
On the flip side, people experiencing severe depressive symptoms tend to have low omega-3 levels and disproportionately high levels of omega-6 fatty acids, which are abundant in processed foods and vegetable oils. This imbalance seems to promote inflammation in the brain. Cod liver oil provides both EPA and DHA, making it a reasonable dietary strategy for supporting brain health, though it isn’t a replacement for treatment in people with clinical depression.
Dosing and Safety Concerns
The biggest risk with cod liver oil comes from its vitamin A content. Unlike beta-carotene from plants, the vitamin A in cod liver oil is preformed retinol, which your body cannot regulate as easily. A single tablespoon contains roughly 13,600 IU, which already exceeds the tolerable upper intake level of 10,000 IU (3,000 mcg) set by the NIH for adults. Most people take a teaspoon rather than a full tablespoon, which brings the dose into a safer range, but it’s easy to overshoot if you’re also eating liver, fortified foods, or taking a multivitamin that contains retinol.
Chronic excess of preformed vitamin A can cause liver damage, headaches, nausea, and skin changes. The risk is especially serious during pregnancy. High retinol intake in the first 60 days after conception is associated with birth defects affecting the heart and central nervous system. The World Health Organization considers daily intakes up to 10,000 IU probably safe after the first 60 days of pregnancy, but UK guidelines are more conservative, advising pregnant women to avoid vitamin A supplements entirely and to skip foods like liver. If you’re pregnant or planning to become pregnant, regular fish oil (which lacks vitamin A) is a safer way to get omega-3s.
How to Get the Most From It
Cod liver oil comes in liquid and capsule forms. Liquid versions are more economical and allow flexible dosing, but they have a strong taste that many people find unpleasant, even in flavored varieties. Capsules eliminate the taste issue but typically deliver a smaller dose per serving, so you may need several to match the nutrient content of a teaspoon of liquid.
Take it with a meal that contains some fat, since vitamins A and D are fat-soluble and absorb better alongside dietary fat. If you’re already taking a multivitamin, check the label for retinol or retinyl palmitate and add up your total vitamin A intake to stay below the upper limit. For most adults, a teaspoon of cod liver oil per day provides a useful boost of omega-3s and vitamin D without pushing vitamin A to risky levels.