Cod liver oil, as the name suggests, is the essential oil extracted from the livers of Atlantic cod (Gadus morhua).
The exact concentration of nutrients in cod liver oil depends on the species of Gadus family the oil comes from.1
The medical use of cod liver goes back centuries. Its first documented medical use was in 1789, when Dr Darbey of the Manchester Infirmary in England used the oil to treat rheumatism.
Only a few decades later, in 1824, cod liver oil was used as a remedy against rickets. By the 1930s the therapeutic properties of cod-liver oil were well established and it was frequently given to children to help prevent rickets and other conditions caused by vitamin D deficiency.2
The difference between cod liver oil and regular fish oils is that fish oils are extracted from the tissue of deep sea oily fish such as tuna, trout, mackerel, herring, salmon and cod. By contrast, cod liver oil is extracted solely from the livers of cod. Cod liver oil contains lower amounts of omega-3 fatty acids than regular fish oils, but larger amounts of vitamins A and D.
Possible health benefits of cod liver oil
Cod liver oil capsules
Apart from being a good source of nutrients, studies have found that cod liver oil may have some very important therapeutic properties.
Cod liver oil is thought to help relieve joint stiffness associated with arthritis, have a positive effect on cardiovascular health, and help repair wounded teeth, nails, hair, and skin.
Let's take a look at the possible health benefits of cod liver oil in more detail. It is important to note that more evidence is required before any health benefit links are proved definitive.
1) Cod liver oil is the right kind of fat
Fat is essential for every single cell in your body. Eating the right kinds of fats (like the omega 3 fatty acids in cod liver oil) will make the skin glow, increase vitamin and mineral absorption and boost the immune system. Fat keeps you full and satiated. When you consume fat, your brain receives a signal to turn off your appetite. Eating healthy fats with a meal helps slow the breakdown of carbohydrates into sugar, which helps to keep blood sugars levels in your blood stable. Your brain needs to be fueled with fat to function optimally.
A German study, which included 43 patients with rheumatoid arthritis who ingested 1 g of cod liver oil every day for 3 months, found that the patients experienced a decrease in the pain intensity of their stiff joints.4
A separate study concluded that cod liver oil may also help those suffering from osteoarthritis. Researchers at Cardiff University found that cod liver oil helped reduce pain and cartilage damage caused by osteoarthritis, as well as reducing the need for joint replacement. In their study, the investigators found that cod liver oil reduced enzymes linked to pain and cartilage damage caused by osteoarthritis.5
3) Age-related macular degeneration
Several studies have suggested that omega 3s support eye health and prevent macular degeneration. These findings have not been consistent in all studies, however. Other nutrients that have been found to be helpful in preventing AMD are carotenoids, which can minimize the damage and reduce the risk of developing age-related macular degeneration. Cod liver oil is also high in carotenoids. Vitamin A was actually first discovered in butterfat and cod liver oil in 1913.15
4) Coronary artery disease
Daily intake of cod liver oil can help prevent coronary atherosclerosis. Research published in the journal Lipids concluded that ingestion of 1.5 g of n-3 fatty acids per day resulted in "decreased progression/increased regression of established coronary artery disease."6
5) Repairing wounds
One study assessed the effect of topically applying cod liver oil ointment on wounds using a hairless mouse ear wound model. The scientists concluded that topical application of 25% cod liver oil ointment "significantly accelerated both the epithelial and the vascular component of healing compared with saline."7
6) Cognitive performance
Cod liver oil contains a high amount of vitamin D. A link between vitamin D and cognitive performance was identified in a study published in the Journal of Neurology, Neurosurgery & Psychiatry. The authors concluded that Vitamin D may play a key role in maintaining good brain function in old age.8
A review of a historical study from 1848 revealed that cod liver oil could be an effective treatment option for tuberculosis. The disease was stabilized in 18% of participants who received cod liver oil, in comparison with only 6% in the control group.9
Cod liver oil is a vitamin D powerhouse
Cod liver oil is one of the richest sources of vitamin D available, providing over 100% of our daily-recommended intake in just one tablespoon. Recent studies have suggested that up to 50% of adults and children worldwide are vitamin D deficient.
Vitamin D deficiency has been associated with osteomalacia and osteoporosis, an increased risk of cardiovascular disease, hypertension, multiple sclerosis, autism, Alzheimer's disease, rheumatoid arthritis, asthma severity and swine flu, however more reliable studies are needed before these associations can be proven.
Vitamin D plays a substantial role in the regulation of calcium and maintenance of phosphorus levels in the blood, two factors that are extremely important for maintaining healthy bones.
Reduced risk of diabetes
Several observational studies have shown an inverse relationship between blood concentrations of vitamin D in the body and risk of type 2 diabetes. In type 2 diabetics, insufficient vitamin D levels may have an adverse effect on insulin secretion and glucose tolerance.3 In one particular study, infants who received 2,000 IU/day of vitamin D had an 88% lower risk of developing type 1 diabetes by the age of 32.
Pregnant women who are deficient in vitamin D seem to be at greater risk of developing preeclampsia and needing cesarean section. Poor vitamin D status is also associated with gestational diabetes mellitus and bacterial vaginosis in pregnant women. It's also important to note that vitamin D levels that were too high during pregnancy were associated with an increase in food allergy of the child during the first two years of life.
Vitamin D is extremely important for regulating cell growth and for cell-to-cell communication. Some studies have suggested that calcitriol (the hormonally active form of vitamin D) can reduce cancer progression by slowing the growth and development of new blood vessels in cancerous tissue, increasing cancer cell death and by reducing cell proliferation and metastases. Vitamin D has an influence in more than 200 human genes, which can be impaired when D status is suboptimal.14
A link between vitamin D and cognitive performance was identified in a study published in the Journal of Neurology, Neurosurgery & Psychiatry. The authors concluded that Vitamin D may play a key role in maintaining good brain function in old age.13
Nutritional profile of cod liver oil
Nutrients in cod liver oil (value per 100g)*3
Vitamin A - 100,000 IU
Vitamin D - 10,000 IU
Saturated fatty acids - 22.608 g
Monounsaturated fatty acids - 46.711 g
Polyunsaturated fatty acids - 22.541 g
Cod liver oil - the forgotten food
In this video, originally featured on America Now, wellness and nutrition expert Peggy Hall discusses the possible health benefits of cod liver oil and the differences between cod liver oil and fish oils.
Potential health risks of cod liver oil
According to research published in the American Journal of Cardiology, large amounts of fish consumption can cause side effects because of environmental toxins in fish such as mercury, polychlorinated biphenyls, dioxins, and other contaminants.
The authors said that "the risks of exposure to environmental toxins and hypervitaminosis with fish consumption are substantially reduced through purification processes used to develop selected concentrated fish oil supplements and prescription preparations."
Therefore, when choosing fish oil therapies, people should be particularly aware of all available information to assess the oils' safety, including US Food and Drug Administration (FDA) or other regulatory labeling.11
The Upper Level (UL) limit recommended for vitamin D is 4000 IU per day. However, the National Institutes of Health (NIH) has suggested that vitamin D toxicity is unlikely at daily intakes below 10,000 IU/day.