As its name implies, Cod liver oil is an oil extracted from the liver of cod. In contrast, other fish oils are usually obtained from the flesh of oily fish such as salmon or tuna. Cod liver oil naturally contains around three times less of the long-chain omega-3 essential fatty acids EPA and DHA than is found in other fish oil products, but these can be concentrated during processing to increase their percentage. Cod liver oil is popular because, unlike other fish oils, it is rich in vitamin A and vitamin D3.
While cod liver oil may be taken as a supplement by those who don’t eat oily fish, it also has a number of other benefits that could help overall health.
Joints: 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 arthritis. Evidence suggests fish oil (including cod liver oil) helps to maintain joint mobility and flexibility and diminish morning stiffness. In people with rheumatoid arthritis, cod liver oil supplements can reduce the number of non-steroidal anti-inflammatory drugs used as painkillers by over 30% after 9 months (i).
Brain: DHA plays an important structural role within brain cell membranes, improving their fluidity so that messages are passed on more rapidly from one cell to another. EPA is involved in cell signalling and also improves communication between brain cells. Populations with high intake of cod liver oil have lower levels of depression (ii).
Heart: The omega 3 content in cod liver oil could also be beneficial for your heart as they have beneficial effects on blood pressure, blood stickiness, inflammation and are prescribed to lower abnormally high blood fat levels. They may also protect against certain abnormal heart rhythms, especially in heart muscle receiving a poor blood supply (iii). An intake of at least 1g omega-3 fish oils per day (from eating oily fish twice a week, or from pharmaceutical grade supplements) has consistently been shown to reduce the risk of sudden cardiac death by 40% to 45% (iv, v, vi).
Bones: Vitamin D3 is essential for absorbing dietary calcium and maintaining strong, healthy bones. Low intakes increase risk of rickets in children and, in adults, of osteomalacia (softening of the bones) and osteoporosis (brittle bones). Cod liver oil is a rich source of vitamin D3, typically supplying 5mcg per dose (the EU recommended daily amount). A study in Aberdeen showed that vitamin D deficiency was lower among women who took CLO supplements compared to women that did not consume these supplements [2.0% vs. 23.7% in Spring (p = 0.001) and 4.5% vs. 24.8% in winter (p = 0.005), respectively] (vii).
Eyes: According to the Royal National Institute of Blind People (RNIB) many studies reveal that vitamin A provided by fruit and vegetables such as tomatoes, raw carrots, green beans and oranges (in the carotenoid form), as well as the retinol form found in cod liver oil, could help maintain healthy cells and tissues in the eye. Omega-3 fish oils, especially DHA, may protect against progression of age-related macular degeneration. A meta-analysis of nine studies, involving almost 89,999 people, found that a high dietary intake of omega-3 fatty acids reduces the risk of developing late AMD by 38%. Eating fish at least twice a week reduced the risk by 24% (viii).
Do not take if allergic to fish.
Cod liver oil products should not be taken during pregnancy as they contain vitamin A, an excess of which can be harmful to a developing baby.
Cod liver oil: 1g - 1.5g per day
Typically a 1g capsule of high-strength fish 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).
If taking a multivitamin as well, check your total intake of vitamins A and D and do not exceed recommended doses. Vitamin A is best limited to less than 5,000 IU (1,500 mcg) per day although intakes of up to 10,000 IU (3,000 mcg) are considered safe. The EU RDA is 5 mcg (200 IU) per day. A daily intake of 25 mcg (1000 IU) is commonly advised to maintain a healthy blood levels of vitamin D during winter months. The European Food Safety Authority suggest a tolerable upper intake level of 100mcg vitamin D per day (4000 IU) (ix).