Cod liver oil is a nutrient-dense oil extracted from the livers of Atlantic or Pacific cod. Unlike regular fish oil, which comes from the flesh of fatty fish like mackerel or sardines, cod liver oil is uniquely rich in both omega-3 fatty acids and naturally occurring vitamins A and D. That combination is what sets it apart from other supplements and explains its centuries-long reputation as a health tonic.
How It Differs From Regular Fish Oil
Both cod liver oil and standard fish oil deliver EPA and DHA, the two omega-3 fatty acids linked to heart and brain health. About 30% of fish oil is pure omega-3s, and cod liver oil contains comparable levels. The key difference is the source organ. Because the liver stores fat-soluble vitamins, cod liver oil naturally contains significant amounts of vitamins A and D that regular fish oil does not. If you’re already getting enough of those vitamins through your diet or a multivitamin, standard fish oil may be all you need. If you’re looking for a single supplement that covers omega-3s plus vitamins A and D, cod liver oil fills that role.
The Nutrients That Matter
Vitamin D is the nutrient most responsible for cod liver oil’s historical importance. Your body needs adequate vitamin D to absorb calcium from food. When vitamin D levels drop, calcium absorption falls, the body compensates by pulling minerals from bone, and the result can be weakened bones. In children, severe deficiency causes rickets, a condition of soft, poorly mineralized bones. Cod liver oil was one of the first effective treatments for rickets, used as early as 1917 by pediatrician Alfred Hess in supplementation programs, years before scientists formally identified vitamin D as the responsible nutrient.
Vitamin A supports immune function, vision, and skin health. Cod liver oil provides it in its preformed state, meaning your body can use it immediately without converting it from plant-based precursors like beta-carotene. This is both an advantage and a risk, since preformed vitamin A accumulates in the body and can cause problems at high doses.
The omega-3 fatty acids EPA and DHA contribute anti-inflammatory effects throughout the body. They play roles in cardiovascular health, brain function, and joint comfort.
Effects on Heart Health
The omega-3s in cod liver oil can meaningfully lower triglycerides, a type of blood fat linked to cardiovascular risk. According to data reviewed by the American Heart Association, people with elevated triglycerides who take therapeutic doses of EPA and DHA see reductions of roughly 20% to 30%. In people with very high triglycerides, reductions can reach 30% or more. These numbers come from studies using prescription-strength doses (about 4 grams of omega-3s per day), which is considerably more than a typical cod liver oil serving provides. A standard dose still contributes to triglyceride management, but the effect is more modest.
Effects on Joint Pain
The evidence on joint health is mixed. In a study of 86 osteoarthritis patients, taking 10 milliliters of cod liver oil daily for 24 weeks showed no significant benefit over a placebo. However, broader research on omega-3 fatty acids and joint pain tells a more encouraging story. In a survey of 125 patients taking omega-3 supplements, 60% reported improvement in overall pain and joint pain specifically. Some controlled studies have found omega-3s comparable to ibuprofen for reducing arthritic pain. The takeaway is that omega-3s may help with joint discomfort for some people, but cod liver oil is not a reliable standalone treatment for arthritis.
How Cod Liver Oil Is Made
Cod livers are substantial, representing about 13% of the fish’s total weight and containing roughly 50% oil. How that oil gets processed matters for the final product’s quality.
Most commercial cod liver oil is refined through molecular distillation, a process that removes contaminants but also strips out much of the naturally occurring vitamins A and D. Manufacturers then add synthetic versions back in. The distillation process also breaks omega-3 fatty acids from their natural molecular structure, and while companies can reassemble them, the resulting molecules differ slightly from what occurs naturally in the fish. High-heat deodorization, another common refining step, can push temperatures above 370°F and may create small amounts of trans fats from the omega-3s.
Raw or unrefined cod liver oil uses a gentler approach, keeping temperatures below 50°F and skipping the distillation, bleaching, and deodorizing steps. This preserves the natural vitamins and keeps the fatty acids in their original form. The tradeoff is a stronger taste and potentially less removal of contaminants.
Fermented cod liver oil, once popular among traditional-food enthusiasts, has come under scrutiny. The fermentation process creates acidic conditions that can accelerate oxidation of the fragile omega-3 fats. Independent lab testing of some fermented brands has found high levels of rancidity markers, and the oil often appears dark brown, a visual indicator of oxidation.
Vitamin A Toxicity Risk
The most important safety consideration with cod liver oil is vitamin A. Because it delivers preformed vitamin A, it’s possible to get too much if you combine it with other vitamin A sources like multivitamins or a diet high in organ meats. Emerging evidence suggests that even intakes only twice the recommended daily allowance for adults are associated with increased risk of osteoporosis and hip fracture. This is somewhat ironic for a supplement taken partly to support bone health.
Pregnant women face the most serious concern. The UK government explicitly recommends that pregnant women and women trying to conceive avoid fish liver oil supplements and liver products entirely, because excess preformed vitamin A can harm fetal development. This guidance applies specifically to preformed vitamin A from animal sources, not to beta-carotene from fruits and vegetables.
Contaminant Concerns
Because cod liver oil comes from the liver, an organ that filters toxins, questions about mercury, PCBs, and dioxins are reasonable. There is currently no regulatory limit for mercury in fish oil supplements or dietary supplements generally. Reputable manufacturers test their products voluntarily and publish results, but the burden falls on consumers to check. Look for brands that provide third-party testing certificates showing levels of heavy metals, PCBs, and oxidation markers. The absence of a universal standard makes brand selection more important than it might be for other supplements.
Choosing and Using Cod Liver Oil
Cod liver oil comes in liquid and capsule forms. Liquid delivers higher doses per serving and costs less per unit, but the taste is distinctly fishy. Capsules are more convenient and mask the flavor, though you may need several to match the dose of a single teaspoon of liquid. Some people find that taking it with food reduces fishy aftertaste and minor digestive discomfort.
When comparing products, check the label for EPA, DHA, vitamin A, and vitamin D content per serving. A product that lists only “omega-3s” without breaking out EPA and DHA separately makes comparison difficult. For vitamin A, stay aware of your total daily intake from all sources, keeping it well within recommended limits, particularly if you take a multivitamin. Products made from wild-caught Atlantic cod with third-party purity testing offer the best combination of nutrient content and safety assurance.