IngredientsCod liver oil (CLO) refers to the oil extracted from the liver of codfish. The primary species used is Gadus morhua (Atlantic cod), though Pacific cod (Gadus macrocephalus) is also used. Based on its tremendous healing powers, cod liver oil extracted from the Gadus morhua species of cod came to be known as "true" cod liver oil.
Cod liver oil is made from the liver of Atlantic cod, a large fish that lives in the very cold ocean waters near Norway and Iceland. The Nordic Seas offer a perfect balance of cold Arctic water and the warm Gulf Stream, creating an ideal climate for the Norwegian-Arctic cod. Ever since the earliest settlements along the coast, cod fishing and products have been crucial for livelihood, economy, and settlement, especially in Northern Norway, where cod fishing has been the very foundation of life.
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.
Cod liver oil is commercially available in several forms:
Peter Möller, the founder of the Möller brand, introduced the Möller method: separating oil from cod liver by steam heating. The liver is steamed at a low temperature, causing the omega-3–rich oil to slowly separate while preserving the natural form of the fatty acids.
Cod liver oil naturally contains many different chemicals and nutrients. The amount of each nutrient in a specific cod liver oil product can change for many reasons, including the area where the cod lived, the weather conditions at that time, and the way that the liver was processed. Most countries sell preparations that have been purified and deodorized, with removal of both toxins and fat-soluble vitamins before vitamin A and D replacement at permissible levels.
The origin of the use of cod liver oil as a food dates back to the Viking Era (late 700s to 1100). Fish and fish liver oil were important parts of the Norse diet. The Vikings consumed most of the fish liver oil during the cold months when the days were shorter and lacked sunlight. Because the winter months were also the prime fishing season, the livers stayed fresh and the oil obtained was also very fresh and of high quality.
The most common method of obtaining fish liver oil used by the Scandinavian Vikings in Northern Norway was as follows: Water in a large pan, rather like a kettle, was brought to a boil. Birch tree branches were placed on top of the pan, and the liver was placed on top of the birch branches. As steam rose, it began to cook the liver, and oil from the liver would begin to drip into the water. The straw-colored oil was skimmed off, and the process was repeated several times. Highly valued for its powers of healing, strength, and energy, the pure, raw oil was called "Gold of the Ocean" by the Vikings of Northern Norway.
Dating back to a time so distant that it is likely difficult to document, fat from the livers of cod and other fish species was used for illumination and heating. Both the Sámi people and the Inuit used fish and seal oil for light and warmth, and from the Middle Ages, the oil became commonly used as lamp oil by other Europeans as well. Various findings from the years 230–895 in Northern Norway suggest that fish, seal, and whale oil were not only produced for local use but also used as trade and barter commodities.
Cod liver oil has a long history in both folk and traditional medicine in northern Europe. Considered a delicacy in Scotland and Norway for centuries, fresh cod liver was revered for medicinal purposes long before Peter Möller invented a modern method to extract its health-giving oil. In the 1750s, Erik Pontoppidan, a professor and bishop, highlighted the health-promoting effects of cod liver oil for both external and internal use.
Cod liver oil is a source of vitamins A and D. It was widely used in the 18th, 19th, and early 20th centuries to treat and prevent rickets, a disease characterized by defective bone growth that is caused by a lack of vitamin D. Widespread fortification of milk with vitamin D in the United States and Europe beginning in the 1930s eliminated rickets as a significant public health problem, and with that, physicians stopped recommending the use of cod liver oil.
It was in the mid-1800s that cod liver oil underwent its first major processing change for centuries. In Norway, a scientist tried to purify cod liver oil to produce a "superior" light brown oil through filtration. Möller's was founded in 1854 by the pharmacist Peter Möller. Peter Möller's dedication and belief in the historical health benefits derived from drinking cod liver oil, rich in omega-3 fatty acids, later led to the discovery of natural vitamin A and D levels which further added to the importance of the product.
Since the 19th century, cod liver oil, for its source of vitamin D, has been used as one of the remedies to cure rickets. It has been the most commonly used supplement in the UK for decades.
Cod liver oil, offered free to all pregnant women, nursing mothers, and children under 5 years old during and after World War 2 in Britain, was banned from ante-natal clinics in the 1990s following recognition of retinol teratogenicity in offspring both experimentally and with maternal intakes >1200 µg (>4000 IU)/day in humans. No replacement vitamin D was provided, and deficiency became common in UK pregnancies, with resurgence of neonatal and childhood rickets (mainly in dark-skinned people, solely breast-fed babies, or unsuitable infant "solids") and fatalities from undiagnosed vitamin D deficiency causing neonatal hypocalcemic status epilepticus and cardiomyopathic heart failure.
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. Cod liver oil is approximately 20% omega-3 fatty acids. CLO also provides vitamins A, D, and E.
Nutritionally important omega-3 fatty acids include α-linolenic acid (ALA) (18-carbon polyunsaturated fatty acid), stearidonic acid (SDA), eicosapentaenoic acid (EPA) (20-carbon polyunsaturated fatty acid), and docosahexaenoic acid (DHA) (22-carbon polyunsaturated fatty acid).
EPA is a 20-carbon omega-3 fatty acid that serves as a precursor for series-3 prostaglandins and series-5 leukotrienes, which possess anti-inflammatory and vasodilatory properties. EPA competes with arachidonic acid (an omega-6 fatty acid) for incorporation into cell membranes and for metabolism by cyclooxygenase and lipoxygenase enzymes. This competitive inhibition reduces the production of pro-inflammatory eicosanoids such as prostaglandin E2 and leukotriene B4.
DHA is a 22-carbon omega-3 fatty acid that is highly concentrated in neural tissue, particularly the brain and retina. It constitutes approximately 40% of the polyunsaturated fatty acids in neuronal cell membranes and 60% in photoreceptor outer segments.
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.
According to the United States Department of Agriculture, a tablespoon (13.6 grams or 14.8 mL) of cod liver oil contains 4,080 µg of vitamin A and 34 µg (1,360 IU) of vitamin D. The Dietary Reference Intake of vitamin A is 900 µg per day for adult men and 700 µg per day for women.
A teaspoon of cod liver oil supplies about 450 IU of vitamin D3, the same form the skin produces in sunlight. That covers a significant portion of the 600 to 800 IU most adults need daily. Cod liver oil's high vitamin D content is what distinguishes it from other fish oils.
Omega-6 fatty acids are present in much smaller quantities, typically comprising less than 2% of total fatty acids. The primary omega-6 in cod liver oil is linoleic acid, with trace amounts of arachidonic acid. The omega-6 to omega-3 ratio in cod liver oil is generally favorable, often around 1:10 or lower, which contrasts sharply with typical Western diets where ratios may exceed 15:1. Saturated fatty acids account for approximately 20–25% of the total fat content, predominantly palmitic acid (C16:0) and myristic acid (C14:0).
Long-chain fatty acids influence inflammation through a variety of mechanisms; many of these are mediated by, or at least associated with, changes in fatty acid composition of cell membranes. Changes in these compositions can modify membrane fluidity, cell signaling leading to altered gene expression, and the pattern of lipid mediator production. Cells involved in the inflammatory response are typically rich in the n-6 fatty acid arachidonic acid, but the contents of arachidonic acid and of the n-3 fatty acids EPA and DHA can be altered through oral administration of EPA and DHA.
EPA and DHA give rise to newly discovered resolvins, which are anti-inflammatory and inflammation-resolving. Increased membrane content of EPA and DHA (and decreased arachidonic acid content) results in a changed pattern of production of eicosanoids and resolvins. Changing the fatty acid composition of cells involved in the inflammatory response also affects production of peptide mediators of inflammation (adhesion molecules, cytokines, etc.).
These fatty acids are able to partly inhibit a number of aspects of inflammation, including leucocyte chemotaxis, adhesion molecule expression and leucocyte-endothelial adhesive interactions, production of eicosanoids like prostaglandins and leukotrienes from the n-6 fatty acid arachidonic acid, production of inflammatory cytokines, and T cell reactivity. In parallel, EPA gives rise to eicosanoids that often have lower biological potency than those produced from arachidonic acid, and EPA and DHA give rise to anti-inflammatory and inflammation-resolving resolvins and protectins.
Omega-3 fatty acid supplements attenuate inflammation by modulating cell membrane function, down-regulating pro-inflammatory cytokines (such as IL-6), reducing production of arachidonic acid derivatives and reactive oxygen species.
The health benefits of cod liver oil, which includes omega-3 fatty acids, have been of considerable interest to medicine due to its promising results. Studies have shown successful therapeutic effects of a high dietary intake of omega-3 fatty acids by reducing the synthesis of very-low-density lipoprotein, with subsequent low levels of serum triglycerides.
Scientists estimate that over a billion people worldwide are vitamin D deficient or insufficient. Vitamin D deficiency is linked to bone fractures in the elderly and abnormal brain development in offspring. It may also lead to the development of metabolic syndrome, which involves the combination of high blood pressure, high glucose levels, and high cholesterol. This can contribute to coronary heart disease, diabetes, and cancer.
Cod liver oil has been used for centuries as a preventative measure against vitamin D deficiency, also called rickets. Historically, people living in northern Europe have relied on cod liver oil as a vitamin D supplement during the winter months when sunlight is scarce. The link between cod liver oil and prevention of rickets is one of the most historically well-established uses in medicine. It was widely used in the 18th, 19th, and early 20th centuries to treat and prevent rickets, a disease characterized by defective bone growth that is caused by a lack of vitamin D.
Evidence strength: The use of cod liver oil (via its vitamin D content) to prevent nutritional rickets is well-established historically and supported by the fundamental understanding of vitamin D metabolism and bone mineralization. The evidence base is largely mechanistic and historical rather than from modern randomized controlled trials specifically testing CLO for this indication.
The n-3 essential fatty acids (EFAs) have previously demonstrated some anti-inflammatory and NSAID-sparing properties. The objective of one key study was to determine whether cod liver oil supplementation helps reduce daily NSAID requirement of patients with RA.
This was a dual-centre, double-blind, placebo-controlled randomized study of 9 months' duration. Ninety-seven patients with RA were randomized to take either 10 g of cod liver oil containing 2.2 g of n-3 EFAs or air-filled identical placebo capsules. Documentation of NSAID daily requirement, clinical and laboratory parameters of RA disease activity and safety checks were done at 0, 4, 12, 24, and 36 weeks. At 12 weeks, patients were instructed to gradually reduce, and if possible, stop their NSAID intake.
A clinical trial showed that 39 percent of patients with RA supplemented with cod liver oil were able to reduce their daily NSAID requirement by greater than 30 percent.
A separate pilot study examined a lower-dose formulation: in this pilot study, 43 patients with rheumatoid arthritis ingested 1 g of cod liver oil (one capsule) daily for 3 months. Decreases occurred in morning stiffness and other markers of disease activity.
Evidence strength: The evidence for cod liver oil as an NSAID-sparing agent in RA is encouraging, with at least one adequately powered double-blind RCT. Results suggest a meaningful reduction in NSAID use in a substantial minority of patients. However, no differences between the groups were observed in the clinical parameters of RA disease activity or in the side-effects observed, indicating that the NSAID-sparing effect may occur without observable improvements in conventional disease activity scores. Evidence is preliminary; larger confirmatory trials are needed.
Observation from past years has revealed that the human population, such as those of Eskimos, has a lower incidence of coronary heart disease, attributed to their seafood-rich diet. One such food is cod liver oil.
A placebo-controlled interventional study in Pakistan examined lipid outcomes: this single-blind, placebo-controlled, two-arm interventional study was conducted in the internal medicine unit of a tertiary care hospital from October 2020 to April 2021. Six hundred treatment-naïve patients with elevated cholesterol levels and/or elevated LDL were enrolled and randomized into two groups. The study group received 415 mg cod liver oil daily as a capsule, in addition to 10 mg rosuvastatin. The control group received 10 mg rosuvastatin with placebo capsules. Participants were followed up on day 30. There were significantly greater reductions in total cholesterol (152.22 ± 29.75 mg/dL vs. 171.65 ± 31.21 mg/dL; p < 0.0001) and LDL (72.41 ± 27.52 mg/dL vs. 79.15 ± 29.12 mg/dL; p < 0.0001) in the intervention group compared to placebo after day 30. The study concluded that cod liver oil in addition to rosuvastatin reduces cholesterol more compared to rosuvastatin alone. Further large-scale trials are needed to examine the role of cod liver oil in reducing lipid values.
An earlier small clinical study in healthy young men found that mean plasma triglyceride concentrations were reduced and those of HDL cholesterol were increased by the supplement. The mean bleeding time was significantly prolonged after 3 weeks of taking the supplement but had returned to the pre-supplementation value 5 weeks after withdrawal.
In a double-blind crossover study in patients with insulin-dependent diabetes and albuminuria, researchers compared the effects of eight weeks of dietary supplementation with cod liver oil versus olive oil on endothelial permeability, blood pressure, and plasma lipid levels in 18 patients. When the patients received the cod liver oil supplement, the mean transcapillary escape rate of albumin decreased from 8.7 ± 0.5 to 6.9 ± 0.6 percent per hour (p < 0.01), and blood pressure decreased from 146 ± 4/90 ± 2 mm Hg to 139 ± 4/85 ± 2 mm Hg (p < 0.05).
At the population level, meta-analyses of trial and/or cohort data have shown no effect of omega-3 fatty acids in supplement form on cardiovascular disease. The EPIC-Norfolk cohort study found that CLO was negatively associated with cardiovascular-related conditions, though this is an observational finding subject to confounding. Causal inferences between CLO and cardiovascular diseases therefore cannot yet be made.
Evidence strength: Preliminary to moderate. Individual trials and metabolic studies show favorable effects on triglycerides, HDL, and blood pressure, but large-scale meta-analyses of omega-3 supplements broadly have not confirmed cardiovascular event reduction. CLO has not been tested in adequately powered cardiovascular endpoint trials independent of general omega-3 supplement research.
The NEEDED (North Sea Race Endurance Exercise Study) was a prospective observational study that: measured CRP concentrations in 1,002 healthy recreational athletes before and 24 hours after a 91-km bicycle race. The use of omega-3 fatty acid supplements was reported in 856 out of 1,002 athletes. Two hundred seventy-four subjects reported regular use of omega-3 fatty acid supplements. One hundred seventy-three of these used cod liver oil (CLO).
Regular users of omega-3 fatty acid supplements had significantly lower basal and exercise-induced CRP levels compared to non-users (p < 0.001). Compared to non-users, regular users had a 27% (95% CI: 14–40) reduction in log-transformed CRP response (unadjusted model), and 16% (95% CI: 5–28, p = 0.006) reduction after adjustment for confounders. CLO was the primary driver of this response with a 34% (95% CI: 19–49) reduction (unadjusted model, p < 0.001) compared to non-users. Corresponding numbers in the adjusted model were 24% (95% CI: 11–38, p < 0.001). Basal CRP levels were reduced and the exercise-induced CRP response was attenuated in healthy recreational cyclists who used omega-3 fatty acid supplements regularly. This effect was only present in regular users of CLO.
Evidence strength: This is observational and therefore cannot establish causation, but the study is large (n = 1,002) and prospective, and the differential effect of CLO versus other omega-3 supplements is noteworthy. Interventional trials specifically testing CLO's effect on CRP are limited.
The Hordaland Health Study provided key population-level data: this study evaluated the association between intake of cod liver oil, rich in omega-3 fatty acids, and high levels of symptoms of depression and anxiety in the general population, using data from the "Hordaland Health Study '97-'99" (HUSK), a population-based cross-sectional health survey from Norway including 21,835 subjects aged 40–49 and 70–74 years. Symptoms of depression and anxiety were measured by the Hospital Anxiety and Depression Scale (HADS). Among the participants, 8.9% used cod liver oil daily. A total of 3.6% had high levels of depressive symptoms. The prevalence of such depressive symptoms among subjects who used cod liver oil daily was 2.5%, as compared to 3.8% in the rest of the population. The findings indicate that regular use of cod liver oil is negatively associated with high levels of depressive symptoms in the general population.
Evidence strength: The evidence here is observational and cross-sectional, meaning it cannot establish causality. The association between CLO use and lower depression symptom prevalence could reflect confounding (e.g., healthier overall lifestyle among CLO users). Interventional omega-3 trials for depression show mixed results depending on the EPA:DHA ratio and the population studied. No large-scale RCT has specifically tested CLO (as opposed to purified omega-3 preparations) for depressive disorder.
A large double-blind RCT investigated CLO in gestational diabetes mellitus (GDM): a total of 550 GDM patients were randomly divided into the intervention group (cod liver oil) and the control group (placebo, mineral oil), and both groups were given regular dietary care. Glycosylated hemoglobin A1c (HbA1c), fasting plasma glucose (FPG), 2-hour plasma glucose (2hPG), lipid profiles, HOMA-IR, and hs-CRP were measured. EPA and DHA were the main components of cod liver oil with 76 mg/mL and 150 mg/mL, respectively. For secondary outcomes, the levels of HbA1c, FPG, 2hPG, triglyceride, total cholesterol, LDL-C, HOMA-IR, and hs-CRP in the intervention group were significantly lower than those in the control group (p < 0.05). The incidence of perinatal complications in the intervention group was also lower than that in the control group (p < 0.05).
Evidence strength: This is a well-powered double-blind RCT in a specific at-risk population. Results on secondary metabolic endpoints are encouraging, but primary glycemic endpoints were not significant between groups. Independent replication is needed.
DHA is a 22-carbon omega-3 fatty acid that is highly concentrated in neural tissue, particularly the brain and retina. It constitutes approximately 40% of the polyunsaturated fatty acids in neuronal cell membranes and 60% in photoreceptor outer segments. The role of DHA in retinal structure provides a mechanistic rationale for CLO's potential relevance to visual health, but clinical evidence specifically from CLO (as distinct from isolated DHA supplementation) in conditions such as age-related macular degeneration or glaucoma is limited and not sufficiently robust for conclusions.
Associations between childhood rickets, sunlight, or cod liver oil and risk of respiratory infections such as TB and pneumonia were recognized a century ago, although it has only been in recent years that the effects of vitamin D on immunity have been revisited and the underlying mechanisms behind its putative effects have started to become more clear. The immunomodulatory role of the vitamin D in CLO provides a plausible mechanistic basis, but high-quality clinical evidence specifically attributing this effect to CLO as a supplement, as distinct from vitamin D supplementation alone, remains preliminary.
The following dosages are those reported in clinical sources and studies, and are presented for informational purposes only:
Each cod liver oil product is different, and a specific product may contain much lower or higher levels of vitamins. Much lower levels may not be helpful for increasing vitamin A and vitamin D levels in your body. Much higher levels may cause serious side effects.
While high doses of vitamin A are usually achieved by vitamin A supplements, hypervitaminosis A can also occur with excessive dietary intake of liver or salt-water fish (cod liver oil). This is a well-established cause of liver injury when used in high doses. Vitamin A in high doses is a direct toxin. Fat-soluble vitamins, like vitamin A, can lead to toxic levels because the body does not excrete excess; it is stored in the liver and fat tissues. The tolerable upper limit for vitamin A for children and adults is 3,000 mcg RAE per day.
A documented case in the medical literature illustrates this risk: an initial case report of hypervitaminosis A described a 3-year-old boy on high doses of vitamin A via daily cod liver oil who developed anorexia followed by listlessness, bone pain, hyperostosis on X-ray, alopecia, hepatosplenomegaly, and anemia, and improved on stopping cod liver oil supplements.
Liver and cod liver oil are very high in vitamin A. Therefore, if you eat liver frequently or use cod liver oil, make sure your supplements do not contain extra vitamin A.
Fish liver oil supplements, such as cod liver oil, contain EPA and DHA, and they also contain vitamins A and D in amounts that vary from product to product. Vitamins A and D can be harmful in excessive amounts. Cod liver oil should not be taken if an individual has very high vitamin D levels, a condition known as hypervitaminosis D.
Cod liver oil may help pregnant women get adequate amounts of vitamin D. However, some experts have cautioned against taking cod liver oil supplements during pregnancy because high vitamin A levels can harm the unborn baby. This concern is supported by the historical British public health experience: cod liver oil was banned from ante-natal clinics in the 1990s following recognition of retinol teratogenicity in offspring both experimentally and with maternal intakes >1200 µg (>4000 IU)/day in humans. If cod liver oil preparations with lower vitamin A contents are generally available, then the vitamin D they contain could contribute to the avoidance of vitamin D deficiency without risking vitamin A toxicity.
The omega-3 fatty acids in cod liver oil may interfere with platelet activity, meaning blood may not clot properly. This may increase the risk of easy bleeding and compound the effects of blood-thinning medications. Use of cod liver oil should be avoided with blood thinners like warfarin. It can increase the blood-thinning effects of the medication, leading to dangerous levels of bleeding. This was also observed in a clinical study where the mean bleeding time was significantly prolonged after 3 weeks of taking the cod liver oil supplement.
Cod liver oil may also interact with certain medications, such as retinoids used for acne or psoriasis, potentially leading to vitamin A toxicity.
To ensure participants' safety in one Norwegian trial, researchers excluded persons with a history of kidney stones, hypercalcemia, renal failure, cirrhosis, or sarcoidosis or other granulomatous diseases from taking cod liver oil.
Cod liver oil is high in omega-3 fatty acids, a valuable aspect in nutrition but one that makes it subject to oxidation, rancidification, and destruction of vitamin A when it is exposed to air. Product quality and storage conditions can therefore meaningfully affect both potency and safety of CLO preparations.
Cod liver oil naturally contains many different chemicals and nutrients. The amount of each nutrient in a specific cod liver oil product can change for many reasons, including the area where the cod lived, the weather conditions at that time, and the way that the liver was processed. Switching to a new bottle or a different brand may result in different effects or side effects because of this variability.
Cod liver oil has been used as a supplement for more than 100 years and thus has an excellent safety record. It is explicitly mentioned under the seafood category in official Norwegian dietary advice. The main constituents, vitamin D and omega-3, have been used in tens of thousands of participants in well-designed studies with very few side effects. Common gastrointestinal effects—common side effects include having a bad taste in the mouth or bad breath, heartburn, nausea, upset stomach, and diarrhea.
Health conditions that Cod liver oil may help support.
Omega-3 fatty acids reduce the inflammatory component of acne by suppressing leukotriene B4 and IL-1 production in skin. Vitamin A, related to the pharmaceutical acne treatment isotretinoin, regulates sebaceous gland activity. Small clinical studies support omega-3 supplementation reducing acne severity.
Vitamins A and D in cod liver oil have antioxidant properties. Vitamin A as retinol quenches singlet oxygen and free radicals; vitamin D regulates antioxidant enzyme expression. Omega-3s reduce oxidative stress indirectly by suppressing inflammatory ROS production. These mechanisms protect cells from oxidative damage.
EPA and DHA reduce neuroinflammation and support neurotransmitter balance implicated in anxiety. Observational data associate omega-3 status with lower anxiety prevalence. Controlled studies show omega-3 supplementation at ≥2 g/day reduces anxiety symptoms, particularly in stressed populations.
Marine oils including cod liver oil reduce inflammatory mediators implicated in arthritic joint pain and swelling. Multiple RCTs demonstrate clinically meaningful improvements in joint tenderness and stiffness. The EPA and DHA content are considered the primary active components.
DHA and EPA from cod liver oil have been studied in ADHD, with some trials showing modest symptom improvements. Low omega-3 status is consistently observed in children with ADHD. A noted review of cod liver oil in children's health reported CLO reduces risk of ADHD in children.
Cod liver oil modulates immune responses implicated in multiple autoimmune conditions via EPA and DHA's anti-inflammatory actions and vitamin D's immunoregulatory effects. Observational data link CLO use in infancy with lower type 1 diabetes risk. EPA and DHA are clinically studied in lupus, and vitamin D deficiency is associated with multiple sclerosis and other autoimmune disorders.
Cod liver oil's EPA and DHA reduce platelet aggregation and thrombus formation by competing with arachidonic acid for thromboxane A2 synthesis. Human studies document prolonged bleeding time with CLO supplementation. These antiplatelet effects contribute to cardiovascular protection.
Cod liver oil produces modest blood pressure reductions, particularly in hypertensive individuals. Clinical and observational data support a small but consistent antihypertensive effect. The 2016 AHRQ evidence review, however, found high-strength evidence of no significant blood pressure effect in supplemented subjects overall.
Cod liver oil provides vitamin D, which is essential for intestinal calcium absorption and bone mineralization. Studies show vitamin D supplementation from CLO supports bone mineral density maintenance and reduces fracture risk, particularly in older adults and those at risk for osteoporosis.
EPA and DHA from cod liver oil suppress matrix metalloproteinases (MMPs) and aggrecanases that degrade cartilage in inflammatory arthritis. Clinical studies in RA show reduced joint damage biomarkers with CLO supplementation. Omega-3s reduce IL-1β-driven chondrocyte apoptosis in vitro.
Cod liver oil's vitamin D has a well-documented scientific and historical role in preventing rickets—a childhood bone disease causing skeletal deformities. After vitamin D deficiency was identified as the cause of rickets in 1920, CLO became the standard prophylactic treatment for decades. Vitamin D supports calcium absorption for bone and tooth mineralization.
Cod liver oil's vitamins A and D regulate immune function in children. Observational data from Norway associate CLO use in the first year of life with lower risk of type 1 diabetes. Vitamin A reduces severity of childhood infections such as measles, and cod liver oil has been used for centuries to support immune resilience in children.
Cod liver oil modestly raises HDL cholesterol and has inconsistent effects on LDL and total cholesterol. A placebo-controlled RCT (600 patients) found CLO plus rosuvastatin lowered LDL and total cholesterol compared to statin alone. Fish oil meta-analyses show a small HDL increase but also a small LDL increase.
Cod liver oil reduces systemic markers of inflammation, particularly CRP. A prospective observational study of over 1,000 athletes found CLO users had 34% lower CRP responses compared to non-users. EPA and DHA inhibit pro-inflammatory cytokine production via the COX-2 and leukotriene pathways.
EPA and DHA reduce neuroinflammatory signaling that sensitizes pain pathways. In RA patients, cod liver oil significantly reduced pain intensity (67.5% reduction in one study). Omega-3 supplementation has broader evidence for reducing chronic pain across musculoskeletal and inflammatory pain conditions.
DHA is the predominant omega-3 in the brain and its concentration declines with aging. A 2022 review of 33 studies found omega-3 supplementation may protect against cognitive decline in healthy individuals without preexisting dementia. Evidence in established Alzheimer's disease is less consistent.
EPA and DHA in cod liver oil are associated with reduced depressive symptoms through anti-inflammatory and neurotransmitter-modulating mechanisms. Multiple observational studies and RCTs support omega-3 supplementation for depression, with EPA showing the strongest antidepressant signal. Evidence is particularly strong in elderly and high-inflammation populations.
Cod liver oil (5–13.56%) is recognized as a safe and effective OTC emollient and skin protectant for diaper rash by the FDA. StatPearls (NCBI Bookshelf) lists it among standard diaper dermatitis emollients. An RCT (Gozen et al., 2014, NICU population) evaluated a 40% zinc oxide with cod liver oil barrier cream formulation for neonatal diaper dermatitis.
Omega-3 fatty acids from cod liver oil reduce ocular surface inflammation implicated in dry eye disease. Multiple RCTs and meta-analyses have examined oral omega-3 supplementation for dry eye, with evidence of improvements in tear break-up time and ocular surface staining. However, a large recent trial (DREAM study) found no significant benefit over placebo.
Omega-3 fatty acids from cod liver oil maintain skin barrier function and hydration by being incorporated into epidermal phospholipids. Vitamin A supports skin cell turnover and barrier integrity. Both nutrients are associated with improved skin moisture and reduced transepidermal water loss.
Omega-3 fatty acids reduce the Th2-mediated inflammatory response underlying atopic eczema. Observational studies link higher maternal and infant omega-3 intake with lower eczema risk. Some RCTs show modest benefit of omega-3 supplementation for eczema severity, though evidence is not fully consistent.
DHA is concentrated in the prefrontal cortex, which governs attention and executive function. Low omega-3 status is associated with attention deficits in children. Supplementation studies show modest improvements in attention and learning in children with low omega-3 status, though effects in ADHD are inconsistent.
Vitamin A in cod liver oil is essential for rhodopsin synthesis in photoreceptors, maintaining visual function. DHA is a major structural component of the retina. Both nutrients support overall eye health, with clinical evidence linking adequate intake to preservation of visual acuity and reduced risk of inflammatory eye conditions.
Cod liver oil addresses multiple age-related processes: it reduces systemic inflammation (inflammaging), supports bone density, slows cognitive decline, protects retinal health, and provides antioxidant support via vitamins A and D. Population-level observational data link long-term omega-3 and vitamin D adequacy with healthy aging outcomes.
DHA from cod liver oil is essential for fetal and infant brain and retinal development. Vitamin A supports cellular differentiation and tissue growth. Vitamin D promotes skeletal development and immune maturation. Together these nutrients support the full spectrum of healthy growth in infants and children.
Cod liver oil contributes to cardiovascular health primarily through triglyceride reduction, modest HDL elevation, and anti-inflammatory and antithrombotic effects. A large interventional study (870 patients) found fewer myocardial infarction events with CLO supplementation. Evidence for broad cardiovascular event reduction is more mixed.
EPA and DHA in cod liver oil improve insulin sensitivity through reduced inflammation and altered adipocyte lipid metabolism. A double-blind RCT in gestational diabetes patients found CLO significantly reduced HOMA-IR and fasting glucose compared to placebo. Omega-3s have been shown to improve insulin resistance in obese and non-obese patients with an inflammatory phenotype.
DHA is highly concentrated in retinal photoreceptors and observational studies consistently associate higher omega-3 intake with lower risk of age-related macular degeneration. However, the large AREDS2 RCT did not find that omega-3 supplementation significantly slowed AMD progression.
DHA is essential for hippocampal neuronal membrane function, synaptic plasticity, and memory consolidation. Supplementation studies show modest memory benefits, particularly in early-stage cognitive decline. Evidence in established dementia is less consistent.
Omega-3 fatty acids from cod liver oil address multiple metabolic syndrome components: triglycerides, blood pressure, insulin resistance, and inflammation. A meta-analysis of 8 RCTs found omega-3 supplementation significantly reduced triglycerides and systolic and diastolic blood pressure in metabolic syndrome patients.
Vitamin A is the biochemical precursor to retinal, the visual pigment in rod photoreceptors responsible for low-light vision. Cod liver oil is a dense source of preformed vitamin A. Deficiency causes night blindness, and supplementation with vitamin A-rich foods like CLO corrects this deficiency.
Cod liver oil's vitamin D supports intestinal calcium absorption and bone mineralization, directly opposing the mechanisms of osteoporosis. Clinical data show vitamin D supplementation increases bone mineral density at the lumbar spine and femoral neck, reducing fracture risk. CLO has been used as an osteoporosis prevention strategy since the 20th century.
Cod liver oil's vitamins A and D support immune reconstitution and tissue repair during recovery from illness. DHA and EPA reduce post-infective inflammation. Evidence from COVID-19 and general upper respiratory infection contexts suggests cod liver oil users have improved recovery trajectories.
DHA from cod liver oil supports fetal brain and retinal development; vitamin D supports fetal bone mineralization. CLO use during pregnancy has been associated with reduced perinatal complications in gestational diabetes. Evidence from a Norwegian study links prenatal CLO use with lower type 1 diabetes risk in offspring.
Fish oil supplementation including cod liver oil has shown beneficial effects in psoriasis in some clinical studies. EPA competitively inhibits arachidonic acid-derived leukotriene B4, a key inflammatory mediator in psoriatic plaques. Omega-3 and vitamin D combinations show promise in reducing plaque severity.
Cod liver oil's EPA and DHA suppress the inflammatory mediators that drive rheumatoid arthritis. Clinical trials have shown reductions in morning stiffness, swollen and painful joints, and NSAID requirements. A double-blind RCT found 39% of RA patients could reduce daily NSAID use by >30% with cod liver oil supplementation.
Cod liver oil addresses two converging drivers of seasonal mood decline: vitamin D deficiency (which peaks in winter) and omega-3 insufficiency. Large observational studies link CLO use with lower rates of depression in populations with limited winter sunlight. Seasonal affective disorder involves both nutrient deficiencies.
Omega-3 fatty acids maintain skin elasticity and hydration by being incorporated into epidermal lipid membranes and reducing inflammatory collagen degradation. Vitamin A in cod liver oil (as retinol) is structurally related to clinically proven anti-aging retinoids, supporting cell turnover and collagen synthesis.
Cod liver oil reliably lowers serum triglycerides, the most robust and consistent lipid effect documented for marine oils. The mechanism involves reduced hepatic VLDL synthesis. Studies show reductions of 15–30% at typical therapeutic doses.
Cod liver oil's vitamin D reduces susceptibility to respiratory tract infections by supporting innate and adaptive mucosal immunity. An observational study (HUNT study, Norway) found regular cod liver oil intake was associated with lower incidence of adult asthma. CLO's anti-inflammatory properties also modulate airway inflammation.
Topical and oral cod liver oil supports wound healing through multiple mechanisms. Vitamin A promotes epithelial cell proliferation; vitamin D supports immune response and tissue repair; omega-3s reduce excessive wound inflammation. An experimental study found topical CLO ointment accelerated wound healing in an animal model.
Body systems that Cod liver oil may help support.
Go back