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Updated November 11, 2019
Since the 1780s, something fishy has been going on in the world of medicine.
Around this time, a doctor in Manchester began prescribing his patients—mainly children afflicted by a condition known as rickets—a supplement of cod liver oil. Caused by a lack of sun exposure, rickets is a debilitating condition, one which this fishy oil seemed to prevent and cure.
The medicinal lore of cod liver oil centers around its use as a fantastic source of vitamin D—hence its ability to cure rickets. However, cod liver oil is also a great source of several other vitamins, nutrients, and fatty acids, meaning it can have wide-ranging health benefits for many people.
As the name suggests, cod liver oil is a dietary supplement which is made from the liver of the cod fish. One tablespoon contains about 123 calories, 14g of total fat (3g saturated), and 78mg of cholesterol. While it’s commonly consumed in liquid form (taken by mouth), you can also find cod liver oil in gel capsules as another way to supplement.
What makes cod liver oil different from other fish oil and omega-3 supplements? The source. Fish oil comes from the bodies of oily fish like mackerel, sardines, herring, anchovies, and salmon. Cod liver oil, on the other hand, comes from pressing the oil from the liver of just one kind of fish—the cod.
Both types of supplements contain high amounts of omega-3 fatty acids. By weight, fish oil actually contains a higher percent of omega-3s.
What makes cod liver special is that it contains high amounts of vitamins A and D—something fish oil doesn’t have. This is because the process isolating fish oils removes most vitamins.
Most fish oil is processed from the fish after canning. Through the isolation and micro-distillation of the oil, vitamins are stripped out, leaving only the EPA and DHA. Fish oil supplements with added vitamin D, vitamins K1 and K2, and astaxanthin are able to pack more of a punch than standard fish oil supplements alone.
What makes this oil particularly potent and rich in nutrients is that it comes from the liver of the fish. It’s packed with essential vitamins and minerals which have accumulated in this nutrient-dense organ.
Our brain, nervous system, eyes, blood, and cellular membranes all need fatty acids to perform functions and protect our health.
In particular, the omega-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA) are a crucial part of any diet. While we can synthesize a small amount of fatty acids like EPA/DHA, others, such as ALA, are essential. This means they must be consumed in the diet, otherwise we can become deficient. For optimal EPA, DHA, and ALA, outside sources are often necessary.
Deficiency in fatty acids leads to problems. Omega-3 deficiencies are associated with metabolic syndrome, brain abnormalities, and non-alcoholic fatty liver disease, among other conditions.
Many Americans are either not consuming enough EPA and DHA, or consuming an improper ratio of omega-6 to omega-3 (we get too many omega-6 fatty acids). Similar to a deficiency, an imbalance can contribute to health issues.
Ideally, the omega-6 to omega-3 ratio should be between 2:1 to 5:1. A typical modern diet is around 15:1 in favor of omega-6. This may be owed to several reasons. Either the food sources of EPA / DHA aren’t being consumed enough, or food sources high in EPA / DHA don’t contain the levels of fatty acids they once did. We're also probably consuming too many foods high in omega-6 fatty acids.
Cod liver oil is a fantastic dietary source of omega-3s, containing about 9% and 14% EPA and DHA by weight, respectively.
Consuming cod liver oil high in omega-3s is a great way to help favor your omega-3 / omega-6 ratio toward the more beneficial omega-3s
When this occurs, they start to “kick out” omega-6 fatty acids from cell membranes and lipids.
Traditional fish oil supplements don’t contain vitamins, but cod liver oil is full of them. 1tsp (5ml) of cod liver oil contains 4500 IU of vitamin A—about 90% of the recommended daily value. A fat soluble vitamin, vitamin A is important for vision, proper immune system function, reproductive health, and for proper functioning of the lungs, kidneys, and our internal circadian rhythms.
Vitamin D levels are also high in cod liver oil. 1tsp contains around 450 IU of vitamin D—112% of the recommended daily value. Vitamin D is one of the most important vitamins around. We need it for proper hormone synthesis, blood pressure control, to fight infections, and to lower the risk of cardiovascular disease.
While beneficial on their own, the nutrients found in cod liver have a more potent effect when consumed together.
This means more health-boosting and disease-protecting properties are present in cod liver oil versus your traditional multi-vitamin. Research has done a lot to back up the anecdotal and historical use of cod liver oil.
One of the most commonly-cited benefits of omega-3 consumption is the ability to prevent chronic inflammation.
Acute consumption 50ml of cod liver oil has been shown to reduce levels of pro-inflammatory molecules like tumor-necrosis factor alpha (TNF-ɑ) inside blood vessels just three hours after consumption.
Another study noted improved endothelial function (the ability to properly regulate the contraction and relaxation of blood vessels as well as blood clotting) following cod liver oil consumption, but this wasn’t accompanied by a decrease in inflammatory markers.
Does cod liver oil influence blood lipids? Several studies have been done in healthy as well as diseased participants with elevated risk factors that lend support to this claim.
Following six weeks of supplementation of 20ml of cod-liver oil in young healthy men, omega-3 quantity increased in their blood.
Supplementing might have more benefits for “at-risk” individuals.
14 months of supplementation with cod liver oil in patients with high cholesterol significantly changed the fatty acid composition of their blood serum to a more beneficial omega-3 dominant profile, which is associated with better metabolic health and lower inflammation.
Nobody likes being sick. Nutrition has long been recognized as one way for people to avoid infections and other ailments.
Other than avoiding being coughed on by your coworkers, preventing illness can be as easy as eating foods and supplements that can strengthen the immune system. Cod liver oil is one of those supplements.
Although most research has been done in children, it seems like cod liver oil may have an impressive ability to suppress infection. A supplement containing a multivitamin mix (selenium and cod liver oil) was shown to reduce pediatric visits for respiratory illness by 36% - 58% throughout the winter and early spring months—times of increases susceptibility.
One interesting experimental study in mice revealed the infection-fighting power of cod liver oil. After six weeks of cod liver oil supplementation, mice which were injected with pneumonia showed increased resistance against the disease, mounting a larger inflammatory immune-defense response against the infection and experiencing less infection-induced cell death (apoptosis).
The mechanism of increased defense is proposed to be due primarily to the omega-3 content of cod liver oil, since omega-3s are known to benefit both innate and adaptive immune system capabilities.
The high content of vitamin D in cod liver oil makes in potentially beneficial for bone health, which requires adequate vitamin D in order to absorb calcium and phosphorous from the foods we eat. This may be especially important for “vulnerable” individuals like older women or those with other risk factors who may also be prone to vitamin D deficiency.
An interesting Norwegian cross-sectional study of cod liver-oil consumers found a negative association between regular intake of cod liver oil and joint pain, with people who experienced more intense pain seeming to gain a more pronounced benefit.
In another observational study, postmenopausal women who had a higher daily intake of vitamin D from cod liver oil also had greater levels of active vitamin D during all seasons of the year—which was associated with less bone resorption and bone loss, and healthy bones.
Seasonal variation in many areas of the world may reduce sunlight exposure throughout the year, and cod liver oil supplementation seems to prevent the low vitamin D associated with a lack of Mr. Sunshine.
For instance, in Norway, values for vitamin D status are 10% - 50% higher during the summer months compared to the winter months due to the variation (i.e. lack of) exposure to ultraviolet rays. It’s no wonder they were the ones to discover the power of cod liver oil.
The anti-inflammatory effects of cod liver oil omega-3s can also benefit musculoskeletal health, and arthritis might be a prime target. Taking 1g of cod liver oil a day (in capsule form) reduced morning stiffness, painful and swollen joints, and pain intensity in patients with rheumatoid arthritis.
Cod liver oil might work similar to a typical non-steroidal anti-inflammatory drug (NSAID). In fact, people suffering from arthritis were able to reduce their use of NSAIDs by over 30% when they instead supplemented with cod liver oil for nine months.
A woman who decides to supplement with cod liver oil might not be the only one to benefit; her child might too. A variety of health benefits and protections have been observed in children of moms who are avid users of cod liver oil.
For instance, pregnant women who supplemented with 10ml of cod liver oil until three months after delivery had children who scored higher on tests of mental processing (higher IQ) compared to children of mothers supplemented with just corn oil.
In another study from Norway, mothers who took cod liver oil during pregnancy gave birth to children with a lower risk of type-1 diabetes.
Evidence that cod liver oil is beneficial for the cardiovascular system is strong like a good heart.
Supplementing with cod liver oil has been shown to lower blood pressure and maintain this reduction for up to five weeks after supplementation ends.
One study investigating how cod liver oil affects blood vessel function in pigs observed that 30ml of cod liver oil per day was able to improve endothelial function and boost the release of beneficial vessel-relaxing substances.
Remember that harmful high omega-6 diet we talked about? Cod liver oil can help with that too.
When a western diet was supplemented with 40ml of cod liver oil per day, omega-6 content of cell membranes was reduced (in favor of omega-3s), and blood platelet reactivity declined—indicating a lower risk for cardiovascular events.
Whether due to a lack of sunshine, poor diet, or other factors, insufficient vitamin D is consistently associated with higher odds of depression.
Similarly, intake of omega-3 fatty acids has been shown to correlate with depression and bipolar disorders.
High in both vitamin D and omega-3s, cod liver oil should then at least be considered as a strategy for boosting mood to enhance mental health and brain function.
One population-based study indicated that people who consumed less cod liver oil had a greater amount of depressive symptoms and cases of major depressive disorder.
While these studies are observational, they all point to the fact that a consistent dietary habit of cod liver oil consumption seems to have great health outcomes for a lot of people. Cod liver oil doesn’t taste good enough just to eat for fun…they must be onto something.
Convinced by the benefits? If so, it’s time to consider what you’ll use and the regimen you’ll follow to get the most from supplementing with cod liver oil.
In terms of which formulation is the best, this might depend on preference. A supplement does no good if its too much to swallow. Some people just have problems ingesting gel caps. In this case, a liquid cod liver oil might make more sense.
There are some nutritional differences between the two forms that need to be addressed. When comparing vitamin A and D content, liquid beats gel. One cod liver oil soft-gel contains about 25% and 34% of your daily vitamin A and D needs, respectively. A teaspoon of liquid, on the other hand, has about 80% and 100% of vitamin A and D.
What about the omega-3s? Again, the liquid form takes the cake. While a soft-gel has about 37mg of EPA and DHA, one teaspoon of cod liver oil liquid has 350mg of each.
Obviously, this inequality could be remedied by ingesting a few more gel caps, but even this has some considerations. Cod liver oil supplements also contain high levels of vitamin A, of which it’s important not to consume too much due to the risk for vitamin A toxicity.
Unfortunately, we don’t have a recommended daily allowance for “cod liver oil” or even any recommended doses to supplement with. Therefore, the dosing for this supplement is based on dietary recommendations of its various components—the omega 3s and vitamins A and D.
For healthy adults, the daily recommendation is about 1 tsp - 4 tsp per day (four on the higher end to treat a deficiency). A standard serving is 1 tsp (5 ml), and unless you think you need more, will probably give you what you need.
Rancid, oxidized oil is good for no one, and could be toxic.
Proper storage (and purchase of the right kind) of cod liver oil is essential to get the most benefits and avoid side-effects.
Liquid oil can be stored in the fridge until opening. After opening, continue to store in the fridge and be sure to use within 90 days. If you won’t use it all within this time, freeze the oil until you plan to use it again.
Soft-gels should NOT be refrigerated—this might actually compromise the gel, causing the liquid inside to oxidize. Store gels in a cool, dark cupboard, where they should last up to two years, although it might be best to replace regularly for safety and freshness.
By nature, these are going to taste a bit fishy. So when supplementing with cod liver oil, many people try to mask the flavor by pairing it with something else. This isn’t as easy to do with gels (we don’t recommend blending or mixing these in with other foods) but can be effective if the liquid form of cod liver oil is used.
Smoothie person? Try blending a dose of cod liver oil in with your morning blend of protein powder and almond milk. Another tactic might be mixing cod liver oil with a splash of lemon juice, some of your favorite yogurt, or even in a scoop (or four) of almond butter.
There aren’t many reasons not to take cod liver oil. While it may interact with some medications like blood thinners, the side effects are generally non-existent (as long as you don’t take too much).
If you already have a strong supplement routine, cod liver oil might be the missing piece to your stack. A unique blend of vitamins and omega-3 fatty acids from a natural fish source make cod liver oil potently healthy. If you’re in need of some extra fatty acids or lacking in one or more critical vitamins, cod liver oil might just be the supplement you’ve been waiting for.
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