Evidence: Very High Possible Benefits: Very High Safety: Reasonable
TABLE OF CONTENTS
What is cod liver oil?
Cod liver oil is a popular supplemental form of omega-3 that also contains a high amount of vitamin A and some vitamin D. Most people use the supplement for improving cognitive, emotional, and cardiovascular health. Unfortunately, cod liver oil is often contaminated with methylmercury and other harmful chemicals, which is why algae oil is almost always a better alternative for most people. This article is about the main benefits of cod liver oil, its potential side effects, the best time to take it, and more.
What does cod liver oil do for the body?
Cod liver oil contains high amounts of vitamin A, vitamin D, and omega 3 fatty acids.
Since omega 3 fatty acids are essential, you need to consume at least some amount of them to survive.
There are 3 main types of omega-3 fatty acids: DHA, EPA, and ALA. ALA (alpha-linolenic acid) is a plant-based form of omega 3 that can be converted into EPA and DHA in the body, but the conversion rate is low, typically less than 5%. This means that a person would need to consume large amounts of ALA to get the same benefits as EPA and DHA.
High intake of ALA has been shown to improve cardiovascular health, blood sugar control, inflammation, cholesterol levels, and more. However, whether or not any of these benefits are specific to ALA or achieved through its conversion to EPA and DHA is not yet clear.
DHA (docosahexaenoic acid) is a major component of the brain and is important for brain development and function. Studies have shown that DHA is associated with improved cognitive function, mood, and mental health. The same also applies to EPA, though to a lesser degree.
DHA is important for the development of the fetus during pregnancy and may be beneficial for the mother’s mental and emotional well-being.
It is also a major component of the retina and is important for eye health. Studies have shown that DHA is associated with a reduced risk of age-related macular degeneration.
EPA (eicosapentaenoic acid) is very effective at reducing triglycerides and symptoms of depression and anxiety.
Both EPA and DHA have anti-inflammatory properties and can help to reduce inflammation throughout the body. This can be beneficial for people with conditions such as rheumatoid arthritis, asthma, and other inflammatory conditions.
Both EPA and DHA have also been shown to have beneficial effects on heart health. EPA has been shown to lower blood pressure, reduce triglyceride levels, and improve the health of the blood vessels. DHA has been shown to improve heart rate variability, which is a measure of the flexibility of the heart. Together, they can help to reduce the risk of heart disease.
Possible benefits
The benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.
Major benefits
Correcting a vitamin A and D deficiency – A severe vitamin D deficiency can have a terrible impact on health and overall quality of life. The symptoms of vitamin D deficiency include mood swings, depression, poor bone health, high blood pressure, multiple sclerosis, severe asthma in children, poor immune system functioning, and much more. If you experience some of these or you know your vitamin D levels are too low, taking the supplement is almost a must. Vitamin A deficiency is not as common but can also lead to a variety of health problems.
Reduced triglycerides – Both EPA and DHA are extremely effective at reducing triglyceride levels. The reductions are in the range of 15-30%. Those with higher baseline triglycerides often see the biggest improvement.
Reduced symptoms of depression – Cod liver oil and other omega 3 supplements are comparable to pharmaceuticals, such as fluoxetine, in majorly depressed people. There is also a lot of anecdotal evidence suggesting that vitamin D supplements can reduce symptoms of depression.
Reduced intensity of measles – The supplement can reduce the risk of measles complications or death in children with measles and vitamin A deficiency.
Reduced symptoms of lupus – The supplement can reduce the symptoms of systemic lupus erythematosus by as much as 50%. Most studies show an improvement of about 30%. Interestingly, doses of 160mg EPA and 140mg DHA work better in this regard than higher doses.
Improved well-being – This benefit applies mainly to depressed individuals but also to those who do not suffer from depression.
Minor benefits
Reduced anxiety – An improvement was observed in medical students and likely applies to anyone with a stressful lifestyle.
Reduced cognitive decline – 900+ mg of DHA has been shown to slow down cognitive decline but lower doses do not seem to have much effect if any.
Improved insulin sensitivity – Vitamin D increases pancreatic insulin secretion, which leads to an improvement in insulin sensitivity. This benefit applies primarily to type 2 diabetics but likely applies to healthy individuals as well.
Improved reaction time – This benefit is relatively mild but applies to most people with low omega-3 intakes.
Reduced symptoms of ADHD – DHA doses of 300+ mg can reduce the negative symptoms of ADHD in children.
Reduced cortisol – This effect is small and likely secondary to the other benefits.
Reduced symptoms of bipolar disorder – The supplement does not directly affect manic phases but it can reduce the symptoms of depression related to BPD.
Improved photoprotection – High doses of omega 3 (1800+ mg of EPA) can reduce the risk of DNA damage, immunosuppression, and erythema in response to sunlight. It can also prolong the time required for sunlight to induce reddening of the skin and prevent sunburns.
Reduced blood pressure – The supplement can reduce blood pressure in those with abnormally high blood pressure. In otherwise healthy individuals, cod liver oil and other omega 3 supplements do not affect blood pressure.
Reduced inflammation – The evidence on this is highly mixed and unreliable. With that said, cod liver oil does seem to positively influence some inflammatory cytokines.
Reduced aggression – This benefit is secondary to improving mood and general well-being.
Increased HDL-C – This benefit is small and only applies to people with unhealthy cholesterol levels. In these individuals, the supplement may also reduce LDL-C and vLDL-C.
Improved exercise-induced oxygenation – This metric is shown to be improved in elite-level athletes. However, it is not as reliable as some fitness influencers claim.
Reduced liver fat – The reduction is seen in people with NAFLD.
Improved memory – The supplement may improve memory but the evidence is limited.
Reduced risk for cancer – Getting to your optimal vitamin D levels reduces the risk for colorectal cancer by around a half. The supplement has also been shown to reduce the risk for some other types of cancer, such as breast and pancreatic cancer, to some degree.
Improved bone health – Vitamin D supplements have been shown to reduce bone fracture risk and increase bone mineral density at doses of 800 IU or more. This amount is found in as little as 8 mL of cod liver oil.
Improved processing accuracy – This improvement was noted in healthy adults and was assessed by the number of errors in a cognitive test.
Increased infant birth weight – Mothers with higher omega 3 intakes (from either food or supplements) give birth to infants with higher birth weights independent of gestational age.
Reduced insomnia – A notable improvement was noted in women with PMS.
Reduced all-cause mortality – Those with optimal levels of vitamin D live longer than those with suboptimal levels. The vitamin slows down aging by keeping your telomere length normal.
Reduced headaches – Women with PMS tend to experience headaches less often and less severely when they take cod liver oil or other omega-3 supplements.
Increased testosterone – While this effect is not too significant, it has been shown consistently in multiple studies that vitamin D supplementation does increase testosterone levels in men. It is important to note that no correlation between the supplement and free testosterone has been found. This effect only applies to total testosterone levels.
Height – While the supplement doesn’t seem to increase height in adults, it can support the growth of children. Those who had higher vitamin D levels in their childhood are overall slightly taller as adults. It is important to point out that no effect of vitamin D on growth hormone levels has ever been noted.
Possible side effects
These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.
Nausea
Stomach cramps
Diarrhea
Fishy aftertaste
Fishy burbs
Blood thinning – Omega-3s can act as blood thinners, so it’s important for people taking blood-thinning medication or about to have surgery to talk to their doctor before taking omega-3 supplements.
Allergic reactions – People who are allergic to fish and seafood should avoid omega-3 supplements made from cod liver oil. Algae oil is usually safe in this regard.
Omega 3:6 imbalance – Omega 3 and 6 have to be kept in balance as too much of one can cause problems if not enough of the other is present. The optimal ratio between the two is somewhere between 1:4 to 4:1. Most people get too much omega 6 and too little omega 3s but if you consume high amounts of fish and take cod liver oil while getting a low amount of omega 6, too much omega 3 can also lead to an imbalance.
Increased LDL-C – Omega 3 supplements like cod liver oil can increase LDL-C by about 5-10% in people with high triglycerides.
Oxidation – Omega 3 from cod liver oil is prone to oxidation and can become a pro-oxidant that can easily cause more harm than good in the body. This is why you need to choose the brand you get omega 3 from carefully and store the supplement well.
Vitamin A toxicity – Mild toxicity can cause liver damage, fatigue, hair loss, nausea, vomiting, dry skin, cracked lips, and headaches. Severe toxicity could lead to death. However, that would only happen if you took extremely high doses of vitamin A or ate certain types of liver in huge quantities. The side effect doesn’t really apply to carotenoids since they are very unlikely to cause toxicity in most people.
Birth defects – Too much vitamin A can cause birth defects, especially in the first 8 weeks of pregnancy.
Imbalance in fat-soluble vitamins – Vitamins A, D, E, and K get broken down in the body by the same mechanism. Since they share the same breakdown pathways, consuming lots of one vitamin may increase the breakdown of the others. So if you take too much vitamin K, your body may turn on this pathway and break down more of the other vitamins as well. Put simply, megadosing one of those fat-soluble vitamins is not the best idea unless you also increase your intake of the other ones. Fortunately, this is not as big of a problem when it comes to supplementing vitamin K as it is with vitamin A, D, or E.
Kidney stones – A higher risk of kidney stones occurs when people take vitamin D together with calcium supplements.
Omega 3 toxicity – While acute toxicity is extremely rare, taking high amounts of omega 3 could lead to chronic toxicity and cause some health problems. To prevent chronic toxicity, it is best to stay below 4 grams a day unless you have a great reason to take more.
Heavy metal toxicity – Fish, krill, and cod liver oils tend to have notoriously high levels of methylmercury in them. This is why it is usually the best option to take algae oil instead of fish oils.
Contamination – Besides mercury, cod liver oils are also often contaminated with PCB, dioxin, and organochlorine.
Who should not take cod liver oil?
You should probably avoid taking the supplement if you:
are willing to take algae oil instead (it is typically much safer and just as beneficial)
experience a severe adverse reaction after taking the supplement
take blood thinners
are pregnant (too much vitamin A can cause birth defects, especially in the first 8 weeks of pregnancy)
suffer from liver disease (too much vitamin A can make the disease worse)
are on a tight supplement budget (since there are more cost-effective supplements on the market for most people)
Who will benefit the most?
You should consider taking the supplement if you:
experience symptoms of vitamin A deficiency or you know you are deficient from blood tests
are on a low-fat diet
consume very little omega 3
eat high amounts of omega 6
have high triglycerides
suffer from depression, ADHD, or bipolar disorder
suffer from lupus
have genetics that make you poor at converting carotenoids to retinol (around 50% of us have an impaired ability to convert carotenoids to retinol by 50-75%)
suffer from hypothyroidism, zinc deficiency, or iron deficiency (since these can hurt the conversion of beta-carotene to retinol)
take calcium (vitamin D helps calcium move from places like joints and arteries where it does more harm than good to places where it’s useful, such as bones)
Different omega 3 supplements
There are many different types of omega 3 oils. The most popular ones include:
Fish oil – Fish oil is the most common supplemental form of omega-3. It is typically made from cold-water fish such as salmon, mackerel, and anchovies. This is usually the cheapest but also the most contaminated type of omega 3 supplement.
Krill oil – Krill oil supplements are a newer form of omega-3 supplement made from small crustaceans called krill.
Cod liver oil – The main difference between cod liver oil and krill oil is that cod liver oil contains a high amount of vitamins A and D. This can be a great thing for people deficient in those nutrients but it can also be problematic for those who already consume too much vitamin A.
Flaxseed oil – Flaxseed oil is a plant-based source of omega-3s, primarily ALA. ALA has a lower conversion rate to EPA and DHA than the other forms of omega-3s, so to get the same benefits as EPA and DHA, a person would need to consume larger amounts of flaxseed oil.
Algae oil – Algae oil supplements are made from a type of microalgae called Schizochytrium sp. which is rich in DHA. These supplements are suitable for vegetarians and vegans. Even if you are not a vegan or a vegetarian, algae oil is superior to the other form in the vast majority of cases because it tends to contain significantly lower levels of contaminants.
What omega 3 supplement is the best?
In the vast majority of cases, algae oil is much safer than fish oil, cod liver oil, or krill oil. This is mainly because algae oil is far lower in contaminants, such as methylmercury, PCB, dioxin, and organochlorine.
Fish oil is usually the cheapest option but also the worst one for health. It is the most contaminated form and doesn’t have additional benefits other than providing omega 3 fatty acids.
Cod liver oil is worth consideration for people who suffer from a vitamin D or vitamin A deficiency. The oil can provide a high amount of both of these nutrients. However, this can also be a bad thing if you already consume too much vitamin A. In that case, you should stay away from cod liver oil and take a different type.
If you do decide to go for cod liver oil because of its vitamin A and D content or for fish oil because of its cheap price, make sure to find a high-quality brand selling non-oxidized, wild-caught oil low in contaminants.
TL:DR, algae oil is almost always the best option.
How much cod liver oil should you take?
1 mL of cod liver oil contains anywhere from 200-1000 IU of vitamin A. If you suffer from a vitamin A deficiency, use cod liver oil primarily to correct the deficiency. If you already get enough vitamin A, other omega 3 oils, such as algae oil, are likely a better option.
The amount of omega 3 in cod liver oil can differ from brand to brand. Fortunately, they almost always specify how much EPA and DHA they contain.
The safe and effective dose range of combined EPA and DHA can be anywhere from 300 mg to 3 grams, depending on your goals.
2 grams of combined EPA and DHA appear to be the best daily dose for most people. This amount should provide most of the benefits without meaningful side effects.
Some people may benefit from doses higher than 2 grams. These include people with high triglyceride levels and rheumatoid arthritis.
Counter-intuitively, some people may benefit more from lower doses than higher doses. For example, people with lupus benefit the most from doses of about 160 mg of EPA and 140 mg of DHA.
Keep in mind that omega 3 should also be kept in balance with omega 6. The optimal ratio between the two is anywhere from 1:4 to 4:1.
The upper safety limit for omega 3 is not well-established. To stay on the safe side, don’t take more than 4 grams of combined EPA and DHA daily unless you have a great reason to do so. Higher amounts may cause problems if you take the supplement for a prolonged period.
Food sources of omega 3
Fish are by far the richest food sources of omega 3 fatty acids, followed by some nuts and seeds.
Here is a list of foods rich in omega 3s and how much they contain: Salmon: 2,200 mg Tuna: 1,000 mg Sardines: 1,800 mg Anchovies: 1,200 mg Mackerel: 1,500 mg Herring: 1,500 mg Flaxseeds: 55,000 mg Chia seeds: 32,000 mg Walnuts: 12,000 mg Spinach: 120 mg Kale: 150 mg
Please keep in mind that the plant sources, such as flaxseeds and chia seeds, mostly contain omega 3s in the form of ALA, which further has to convert into EPA and DHA and the conversion rate is relatively small.
Therefore, if you are a plant-based eater or avoid fish, it may be a good idea to supplement with omega 3s.
While some nuts and plant oils are high in omega 3, they also tend to be very high in omega 6 and therefore typically do not support a good balance between omega 3 and 6.
Best time to take cod liver oil
Omega 3 fatty acids and vitamins A and D from cod liver oilare fat-soluble so make sure to take the supplement with food to absorb it well.
Whether you take the supplement in the morning or the evening doesn’t matter much.
Unless it feels too impractical, spread the daily dose into 2+ smaller doses throughout the day.
Interactions
Omega 6 Omega 3 and 6 have to be kept in balance as too much of one can cause problems if not enough of the other is present. The optimal ratio between the two is somewhere between 1:4 to 4:1.
Vitamin E Vitamin E protects omega 3 fatty acids from oxidizing, both inside and outside the body. It is important to note that if omega 3 fatty acids have already oxidized, vitamin E cannot fix them back to normal. Taking vitamin E with oxidized cod liver oil will not make it beneficial or non-harmful. With that said, the more omega 3 fatty acids you take, the more vitamin E you will need.
Green tea Omega 3 fatty acids increase the bioavailability of EGCG and other catechins in tea.
Turmeric Turmeric and omega 3 appear synergistic for reducing breast cancer cell proliferation. In theory, this combination may also lead to increasing BDNF (brain-derived neurotrophic factor) but more evidence is needed to support this.
Fucoxanthin These two supplements may be synergistic for anti-obesity effects.
Statins Omega 3 works synergistically with statins in terms of improving cardiometabolic parameters.
Where to buy cod liver oil
Which brand you chose will have an enormous effect on how you react to the supplement. Unfortunately, many brands sell oxidized cod liver oils or capsules which are likely to do more harm than good.
Amazon is the best option for ordering omega 3 supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.
Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.
FAQ
You can take the fatty acid daily and do not need to cycle it. However, it is certainly not a problem if you don’t take it every day. Not taking the supplement every once in a while could lead to better absorption. That is yet to be proven or disproven.
All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, you may need a highly accurate scale to dose them correctly (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes some time that can add up over months or years. The disadvantage of capsules is that they often contain bovine gelatin, which rarely comes from an ethical source.
Yes. Most fatty acids, including omega 3 in cod liver oil, absorb and digest well if you take them before falling asleep. The supplement should not impact sleep quality in any significant way.
Cod liver oil can oxidize and become harmful if kept in bad conditions. Unfortunately, many omega 3 supplements are already heavily oxidized by the time you buy them, which is why choosing a high-quality brand is important.
Keep the supplement in a cold, dark, and dry place, and it should remain just as potent for many months.
Yes. The main issue in this regard is that cod liver oil contains a very high amount of vitamin A (anywhere from 200-1000 IU per mL). Too much vitamin A can lead to toxicity and an imbalance in other fat-soluble vitamins. Many cod liver oils also contain high levels of mercury and other harmful chemicals. It is best to stay below 4 grams of combined EPA and DHA a day to prevent these side effects.
You may need more of this fatty acid if you: – don’t get enough omega 3 from food – consume too much omega 6 – wish to lower your triglycerides – suffer from lupus – suffer from depression, ADHD, or bipolar disorder – eat high amounts of omega 6 – consume very little omega 3
The half-life of DHA in the body is about 3 days. For EPA, it is about 5 days. ALA only stays in your body for a few hours before it gets utilized.
In the long term, you need to take the supplement for about 2-4 weeks to begin noticing the benefits.
Cod liver oil is not vegan-friendly. However, you can buy algae oil that is vegan-friendly and is often superior to other sources of omega-3 because it is generally not as contaminated with mercury and other harmful chemicals. If you buy algae oil in a capsulated form, beware that the capsules often contain animal-based gelatin. Instead, find a brand that puts its products into cellulose capsules.
Omega 3 fatty acids and vitamins A and D from cod liver oil are fat-soluble, so you need to take them with food to absorb them well.
Cod liver oil should not break a fast unless you take a very high dose at once (anything under 20 grams should be safe). If you practice time-restricted eating, take cod liver oil during your eating window to make sure it absorbs well and doesn’t break your fast.
References
Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything said in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.
