Cod liver oil contains three key nutrients that set it apart from other supplements: omega-3 fatty acids (EPA and DHA), vitamin A in its preformed retinol form, and vitamin D3. It’s extracted from the livers of Atlantic and Pacific cod, which is why it carries fat-soluble vitamins that regular fish oil doesn’t. One teaspoon provides roughly 450 IU of vitamin D and meaningful amounts of vitamin A, along with a dose of the same omega-3s found in standard fish oil capsules.
The Core Nutrients in Cod Liver Oil
Cod liver oil delivers its benefits through a handful of compounds that each play distinct roles in the body. The exact amounts vary between brands and products, but every bottle contains the same basic profile.
EPA and DHA: These are long-chain omega-3 fatty acids, the same ones found in salmon, mackerel, and fish oil supplements. EPA helps regulate inflammation, while DHA is a structural component of brain tissue, the retina, and cell membranes throughout the body. Prescription-strength omega-3s (4 grams per day) can lower triglycerides by 20% to 30%, though a standard teaspoon of cod liver oil provides far less than that therapeutic dose.
Vitamin A (retinol): Unlike the beta-carotene in carrots and sweet potatoes, the vitamin A in cod liver oil is preformed retinol, which the body can use immediately without converting it. Retinol supports vision, immune function, and skin cell turnover. This is also the nutrient that makes dosing matter most with cod liver oil, since preformed vitamin A can accumulate in the liver.
Vitamin D3: A teaspoon of cod liver oil supplies about 450 IU of vitamin D3, the same form your skin produces in sunlight. That covers a significant portion of the 600 to 800 IU most adults need daily. Vitamin D helps the body absorb calcium, supports bone density, and plays a role in immune regulation.
Beyond these three, cod liver oil contains smaller amounts of other fat-soluble compounds, including vitamin E and trace fatty acids, but these exist in quantities too small to be nutritionally significant on their own.
How Cod Liver Oil Differs From Fish Oil
The confusion between cod liver oil and regular fish oil is understandable since both come from fish and both contain EPA and DHA. The difference is the source. Regular fish oil is extracted from the flesh of oily fish like mackerel, herring, tuna, and salmon. Cod liver oil comes specifically from the liver of cod, which is where the fish stores fat-soluble vitamins.
This organ-versus-flesh distinction is why cod liver oil naturally contains high levels of vitamins A and D, while standard fish oil contains little to none of either. On the flip side, many fish oil supplements are concentrated to deliver higher doses of EPA and DHA per capsule than cod liver oil typically provides. So the trade-off is straightforward: cod liver oil gives you a broader nutrient package with moderate omega-3s, while fish oil gives you more omega-3s without the vitamins.
Why Vitamin A Levels Need Attention
The preformed vitamin A in cod liver oil is the main reason you can’t treat it like a regular fish oil and simply take more for extra omega-3s. The tolerable upper intake level for preformed vitamin A in adults is 3,000 mcg per day. For children ages 1 to 3, it drops to just 600 mcg. Going over these thresholds regularly can stress the liver and, during pregnancy, poses a risk of birth defects.
Because vitamin A concentrations vary significantly between brands, checking the label matters more with cod liver oil than with most supplements. Some products are formulated to keep vitamin A moderate while boosting omega-3 content. Others retain the naturally high vitamin A levels found in cod liver. If you’re already eating liver, fortified dairy, or taking a multivitamin with retinol, those sources all add up against the same daily ceiling.
How It’s Processed and Purified
Raw cod liver oil can contain environmental contaminants, including heavy metals, PCBs, and flame retardants, that concentrate in the fish’s liver over its lifetime. Modern manufacturers use molecular distillation, a process that heats the oil under vacuum to separate and remove these pollutants without destroying the oil itself.
The industry measures freshness through oxidation values. The global standard, set by the industry trade group GOED, caps total oxidation (called TOTOX) at 26. This number reflects how much the oil’s fatty acids have broken down through exposure to heat, light, or air. A TOTOX value below 26 means the oil hasn’t gone rancid, which matters both for safety and for the fishy taste and smell that put many people off. Reputable brands test each batch and publish these values, so if a product smells strongly of fish or tastes bitter, that’s a sign of oxidation rather than a normal characteristic.
What the Oil Actually Looks Like
Liquid cod liver oil is a pale yellow oil with a mild, slightly fishy flavor. Flavored versions often add lemon or mint to mask the taste. Capsule forms enclose the same oil in a gelatin or plant-based shell that dissolves in the stomach, bypassing the taste entirely. The oil is calorie-dense like any fat, at roughly 40 calories per teaspoon, though the serving size is small enough that this rarely matters in the context of a full diet.
Some products are labeled “fermented cod liver oil,” meaning the liver was broken down through a fermentation process rather than heat extraction. Proponents claim this preserves more nutrients, but there’s no regulatory standard defining what fermented cod liver oil must contain, and vitamin levels in these products can be unpredictable. Standard molecularly distilled versions offer a more consistent and tested nutrient profile.