Cod liver oil, as its name suggests, is an oil extracted from the liver of cod. This differs from other fish oils which are obtained from the flesh of oily fish, such as salmon or tuna, or from crustaceans such as krill oil. Cod liver oil health benefits relate partly to its long-chain omega-3 fatty acids, EPA and DHA, and partly to its high levels of vitamin A and vitamin D3.
Fermented cod liver oil
The traditional method of extracting cod liver oil from cod livers is by fermentation. The cod livers are soaked in brine and fermented by salt-tolerant, lactic acid bacteria which convert liver glycogen (a form of starch) to lactic acid. This fermentation process releases free fatty acids, vitamin A, vitamin D and other fat-soluble liver components, which float to the top and are drained off. Fermented cod liver oil also includes some vitamin K produced by the fermenting lactic acid bacteria.
Fermented cod liver oil is strong-smelling and has a tart, acid taste which is sometimes ‘diluted’ with butter fat to improve the flavour.
Modern processing methods separate the cod liver oil using gentle heat and/or solvents. Distillation then removes impurities such as mercury and dioxins, as well as saturated fats and other unwanted substances, including the more smelly amino acid breakdown products. This process also removes the vitamin A and vitamin D3 which is added back in.
Some people prefer fermented cod liver oil, as it retains the natural vitamins, although these are present in variable amounts that may be significantly higher than other forms of cod liver oil. Others prefer ‘pure’ deodorise cod liver oil, which has a known amount of both vitamin A and vitamin D added back in.
Cod liver oil health benefits
Because fish livers concentrate fat soluble vitamin A and vitamin D3, cod liver oil is a rich source of these important nutrients. While cod liver oil naturally contains around three times less omega-3 than other fish oils, these can be concentrated by modern distillation processes to increase their percentage to an equivalent amount – check labels to see how different brands compare.
Cod liver oil benefits
Cod liver oil was traditionally given to children as a source of vitamin D, both to prevent and treat rickets. Cod liver oil is now widely used to reduce joint pain and boost immunity – especially during winter months when the ability to make vitamin D in the skin is restricted.
In Russia, doctors prescribe cod liver oil clinically to prevent further furring up of the arteries (atherosclerosis) in people with arterial disease, to lower triglyceride levels, and to treat rheumatoid arthritis joint pain.
Cod liver oil and kids immunity
Vitamin D plays an important role in immunity and, by reducing the frequency and severity of colds, can protect against asthma, reducing the chance of experiencing a severe asthma attack or having to go to hospital. The omega-3 in cod liver oil also has an anti-inflammatory effect to reduce airway sensitivity.
During winter and spring, a hospital clinic in New York gave 1 teaspoon of a lemon-flavoured cod liver oil to infants and young children, together with a children’s multivitamin and mineral supplement that included selenium and other trace elements.
A similar clinic 1.1 miles away enrolled a control group that were not given the cod liver oil and multivitamin supplements.
During that year’s cough and cold season, the number of paediatric clinic visits for upper respiratory tract infections was reduced by 36% to 58% in those taking the cod liver oil and vitamin supplements.
There was no change in the control group who had just as many coughs and colds as usual.
Cod liver oil and osteoarthritis
Omega-3 fatty acids, especially DHA and EPA, are converted in the body into substances (series 3 prostaglandins and series 5 leukotrienes) that reduce inflammation. The anti-inflammatory properties in cod liver oil are beneficial for joint health and the symptoms of osteoarthritis. Anecdotal evidence suggests that cod liver oil helps to maintain joint mobility and flexibility while reducing pain.
Surprisingly, this has not been widely researched. A study from Cardiff University assessed the effects of taking 2g cod liver oil or placebo every day in 31 people with osteoarthritis of the knee who were scheduled to have knee replacement surgery. At the time of operation, 10 to 12 weeks later, 86% of those taking cod liver oil had absent or significantly reduced levels of the enzymes that cause cartilage damage and joint pain, compared to 26 per cent of those taking placebo. The professor of orthopaedics who led the trial suggested that people with sporting injuries which increase the chance of early onset osteoarthritis should consider taking cod liver oil to slow the progression of joint deterioration.
Cod liver oil and rheumatoid arthritis
Rheumatoid arthritis is an autoimmune inflammatory disease in which the synovial lining of certain joints becomes swollen and inflamed. The use of non-steroidal anti-inflammatory drugs (NSAIDs) to reduce pain is limited by side effects and a concern about long-term health risks. Cod liver oil can help by reducing pain and morning joint stiffness.
In a pilot study, 43 people with rheumatoid arthritis took 1g of cod liver oil (one capsule) daily for 3 months. This reduced morning stiffness by 52.4%, painful joints by 42.7%, swollen joints by 40% and pain intensity by 67.5%. Around 7 out of 10 rated cod liver oil as good or very good for improving their symptoms.
Another study then compared the effects of cod liver oil against placebo in 97 people with rheumatoid arthritis, who took either 10g of cod liver oil (containing 2.2 g of EPA + DHA) or identical placebo capsules every day for 9 months. After 12 weeks treatment, they were asked to gradually reduce and, if possible, stop taking their NSAID painkillers. Of those who took cod liver oil for at least 9 months, 59% were able to reduce their daily use of NSAIDs by more than a third compared with 19% of those taking placebo. This study suggests that cod liver oil supplements can help to reduce the need for NSAID painkillers in people with rheumatoid arthritis.
Cod liver oil and heart health
The omega 3 content of cod liver oil will have the same beneficial effects on blood pressure, blood stickiness, and triglyceride fat levels as omega-3 fish oils. high blood fat levels.
Taking cod liver oil helps to thin the blood by reducing platelet aggregation and the formation of unwanted blood clots. The omega-3 fatty acids in cod liver oil may also protect against certain abnormal heart rhythms, and reduce the risk of complications following a heart attack.
In men who had experienced a heart attack, taking cod liver oil supplements significantly lowered levels of triglyceride fats for 6 weeks while they were taking the supplements, compared to another 6 week period when they did not take them.
Taking cod liver oil does not have a significant effect on total cholesterol or ‘good’ HDL cholesterol levels, however.
Cod liver oil and depression
Cod liver oil supplies the long-chain omega 3 fatty acids, DHA and EPA, which improve the fluidity of brain cell membranes, and promote optimum communication between brain cells. In countries where cod liver oil is a popular supplement, there is a lower risk of depression.
A study from Norway, for example, which involved 21,835 adults, those who took cod liver oil every day were 29% less likely to have depressive symptoms than non-users after adjusting for all other factors, including smoking habits, coffee and alcohol consumption, level of exercise and education.
Cod liver oil and bone health
Vitamin D3 is essential for absorbing calcium and phosphorus from the diet to maintain strong, healthy bones. Low intakes of vitamin D can lead to rickets in children and to osteomalacia (softening of the bones) and osteoporosis (brittle bones) in adults, and this was one of the main reasons why cod liver oil was originally recommended.
Cod liver oil is an excellent source of vitamin D3. A study from Aberdeen in Scotland found that the level of vitamin D present in cod liver oil supplements was sufficient to prevent vitamin D deficiency throughout the year in most of the postmenopausal women studied – even during winter. Only 4.5 % of those taking cod liver oil supplements developed a vitamin D deficiency during winter, compared to 24.8% of those not taking cod liver oil supplements.
The best cod liver oil supplements
The usual recommended dose is 1g – 2g cod liver oil per day.
Cod liver oil is available as a liquid or capsules. If you like strong flavours, you can take fermented cod liver oil, but if you prefer less fishy flavours, then deodorised versions that are flavoured with essential oils offer a better taste experience.
Typically a 1g capsule of cod liver oil contains around 500mg of the important long-chain omega-3 fatty acids, EPA and DHA. Those described as high or extra high strength provide the highest amount of omega-3 fatty acids (check labels).
Modern manufacturing processes remove impurities and pollutants, but this also removes some of the fat soluble vitamin A and D which must be replaced. Check labels to ensure that these important vitamins have been added back.
One teaspoon of cod liver oil produced by traditional cold pressing or fermentation typically provides 400 IU (10 mcg) vitamin D3.
Some processed cod liver oils provide only 1IU to 20 IU vitamin D per teaspoon (5 ml) while some cod liver oil is fortified to provide a concentrated amount of 1,000 IU (25 mcg) vitamin D per teaspoon.
Cod liver oil side effects
Obviously, do not take cod liver oil if you are allergic to fish.
Do not take cod liver oil (or any other liver products, including eating liver) during pregnancy as excess vitamin A can be harmful to a developing baby.
If you are already taking a multivitamin, check your total intake of vitamins A and D do not exceed recommended doses.
The safe upper level for vitamin A is 5,000 IU (1,500 mcg) per day from both food AND supplements in the UK. The EU and US suggest a tolerable upper level from both food and supplements is 3000 mcg per day for men and women of child-bearing age (post-menopausal women may need more to reduce the risk of bone fractures).
If taking both a multivitamin and a cod liver oil, check the combined amount of vitamin A does not exceed the recommended daily amount of 800 mcg (2,664 IU) which leaves room for the amount likely to come from your food.
For vitamin D, the European Food Safety Authority suggest a tolerable upper intake level of 100mcg vitamin D per day (4000 IU).
What NOT to do with cod liver oil
Urologists in Qatar had to treat 8 patients who had cod liver oil injected beneath the skin of the penis to increase its size. This lead to a range of serious side effects, including swelling of the foreskin, abscesses and tissue destruction, all of which required emergency surgery. The urologists stated that increased public awareness was needed to avoid this problem which is the only reason I mention it here. Don’t do it!