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cod

Also known as: Cod, Atlantic cod, Cod liver oil, CLO, Gadus morhua

Overview

Cod refers primarily to fish species in the genus *Gadus*, with *Gadus morhua* (Atlantic cod) being the most common. Cod liver oil (CLO) is a dietary supplement derived from the liver of cod fish, renowned for its rich content of omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), as well as fat-soluble vitamins A and D. It is primarily used to supplement these essential nutrients, offering benefits for cardiovascular health, anti-inflammatory processes, and metabolic support. The supplement is well-studied, with a high level of research maturity, including numerous randomized controlled trials and meta-analyses supporting its efficacy. Its key characteristics include its high concentration of beneficial fatty acids and vitamins, making it a valuable nutritional supplement for various health applications.

Benefits

Cod liver oil offers several evidence-based benefits, primarily driven by its omega-3 fatty acid content. For cardiovascular health, meta-analyses and randomized controlled trials (RCTs) have shown that fish oil supplementation, including cod liver oil, can reduce cardiac events and mortality, particularly post-myocardial infarction. For instance, studies have reported a 25-29% reduction in total cardiac events. It exhibits significant anti-inflammatory effects, with regular use associated with a 24% reduction in C-reactive protein (CRP) levels, a key marker of systemic inflammation. Furthermore, cod liver oil can improve metabolic parameters, such as liver enzymes (ALT, AST) and insulin resistance, in individuals with metabolic dysfunction-associated steatotic liver disease (MASLD), especially at doses below 2000 mg/day and with durations exceeding 12 weeks. While some evidence suggests it may reduce pro-inflammatory cytokines and improve immune function, its effects on fat mass reduction are modest and inconsistent. Benefits are particularly notable in patients with cardiovascular disease, MASLD, and chronic low-grade inflammation, with clinically significant reductions in cardiac events and inflammatory markers observed over months to years of consistent use.

How it works

The primary mechanism of action for cod liver oil stems from its omega-3 fatty acids, EPA and DHA. These fatty acids integrate into cell membranes, altering their fluidity and function. They serve as precursors for specialized pro-resolving mediators (SPMs) and modulate the synthesis of eicosanoids, shifting the balance from pro-inflammatory to anti-inflammatory compounds. EPA and DHA also interact with nuclear receptors like PPARs and inhibit inflammatory signaling pathways such as NF-κB, thereby reducing the production of pro-inflammatory cytokines. This modulation impacts the cardiovascular system by promoting anti-arrhythmic and anti-thrombotic effects, the immune system by reducing cytokine production, and liver metabolism by improving insulin sensitivity and reducing steatosis. Cod liver oil is well absorbed orally, and its fat-soluble vitamins A and D further contribute to its nutritional value.

Side effects

Cod liver oil is generally considered safe when consumed at recommended doses. The most common side effects are mild and include gastrointestinal discomfort and a fishy aftertaste. At higher doses, there is a possible increased risk of bleeding due to its antithrombotic effects, although this is uncommon. Rare side effects include vitamin A toxicity (hypervitaminosis A) if the supplement is overdosed, and hypervitaminosis D, which is also rare but possible. Cod liver oil may interact with certain medications, particularly enhancing the effects of anticoagulants and antiplatelet drugs, increasing the risk of bleeding. It is contraindicated in individuals with bleeding disorders or a known allergy to fish. Special caution is advised for pregnant women regarding vitamin A intake, as excessive amounts can be teratogenic, necessitating careful monitoring of total vitamin A consumption from all sources.

Dosage

For cardiovascular benefits, a minimum effective dose of approximately 500 mg/day of combined EPA+DHA has been observed. Optimal dosage ranges typically fall between 500-1800 mg/day of EPA+DHA, as seen in various randomized controlled trials. For metabolic benefits, particularly in MASLD, doses below 2000 mg/day of EPA+DHA are recommended. Cod liver oil doses vary, but a typical teaspoon usually provides around 400-1000 mg of EPA+DHA. The maximum safe dose for omega-3 fatty acids is generally considered up to 3000 mg/day of EPA+DHA; however, the vitamin A and D content in cod liver oil limits its overall dosage to prevent toxicity from these fat-soluble vitamins. Benefits accrue over weeks to months, so consistent daily intake is recommended. Cod liver oil is available in liquid or capsule forms, and it is best absorbed when taken with meals containing fat. No specific cofactors are required, but a balanced diet supports its overall efficacy.

FAQs

Is cod liver oil safe for long-term use?

Yes, cod liver oil is generally safe for long-term use, provided it is dosed appropriately to avoid excessive intake of vitamin A, which can accumulate in the body.

Does cod liver oil reduce inflammation?

Yes, cod liver oil has been shown to significantly reduce markers of inflammation, such as C-reactive protein (CRP), and can lower pro-inflammatory cytokines.

How soon will benefits appear?

Improvements in inflammation markers can be observed within weeks of consistent use, while more significant benefits, such as those for cardiovascular health, may require several months to years to manifest.

Is cod liver oil better than other fish oils?

Cod liver oil provides the added nutritional benefit of naturally occurring vitamins A and D, in addition to omega-3s. This can be advantageous but also requires careful consideration of total vitamin intake to avoid toxicity.

Research Sources

https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2025.1524830/full – This systematic review and meta-analysis of RCTs found that fish oil supplementation, including cod liver oil, significantly reduced liver enzymes (ALT, AST) and improved metabolic parameters in MASLD patients. Benefits were most pronounced at doses below 2000 mg/day and durations exceeding 12 weeks, highlighting its potential in managing metabolic liver disease.
https://pmc.ncbi.nlm.nih.gov/articles/PMC8240263/ – This observational study found that regular cod liver oil use was associated with a 24% lower level of C-reactive protein (CRP), a key marker of systemic inflammation, compared to non-users. The findings suggest a significant anti-inflammatory effect of cod liver oil in a general population setting.
https://www.ahajournals.org/doi/10.1161/01.cir.0000038493.65177.94 – This review of RCTs and meta-analyses concluded that fish oil supplementation consistently reduced cardiac events by approximately 25-29% and decreased mortality post-myocardial infarction. The evidence supports the significant role of fish oil, including cod liver oil, in secondary prevention of cardiovascular disease.
https://www.tandfonline.com/doi/full/10.1080/10408398.2018.1425978 – This systematic review explored the effects of high DHA fish oil on inflammatory markers and immune function. It reported that DHA-rich fish oil reduced pro-inflammatory cytokines and improved immune cell function, although results regarding fat mass reduction were inconsistent across studies.