cod-liver oil

Oil obtained primarily from the liver of the Atlantic cod and related fish. It is principally a mixture of the glycerides (see glycerol) of many fatty acids, but its minor constituents, the fat-soluble vitamin A and vitamin D, give it its importance. It was once used to treat and prevent rickets, but the widespread fortification of milk with vitamin D in the United States and Europe beginning in the 1930s eliminated rickets as a significant public health problem. It is still used as a remedy for joint pain caused by arthritis and as a preventive of cardiovascular disease, although these benefits have not been proven scientifically. It is also used in feeds for poultry and other animals.

Learn more about cod-liver oil with a free trial on Britannica.com.

This article is about the fish extract, for the traditional Newfoundland song, see "Cod Liver Oil (song)".

Cod liver oil is a nutritional supplement derived from liver of cod fish. It has high levels of the omega-3 fatty acids, EPA and DHA, and very high levels of vitamin A, and vitamin D. It is widely taken to ease the symptoms of arthritis as well as other health benefits. It was once commonly given to children.

Characteristics

Depending on the quality of the oil, the flavor and aroma range from a mild sardine-like flavor, to an intense and obnoxious odor of rotten fish and rancid oil. High quality cod liver oil is a pale-yellow, thin, oily liquid, having a peculiar, slightly fishy, but not rancid odor, and a bland, slightly fishy taste. Manufacturers sometimes add flavorings, such as citrus or mint essence, to cod liver oil to make it more palatable.

Manufacture

Cod liver oil is made by cooking cod livers with steam, and then pressing/decanting the cooked livers to extract the oil. This is in contrast to fish oils, which are extracted from the cooked whole body tissues of fatty fish during the manufacture of fish meal.

Therapeutic uses

Cod liver oil is widely taken to ease the pain and joint stiffness associated with arthritis, but has also been clinically proven to have a positive effect on heart, bone, and brain, as well as helping to nourish skin, hair, and nails.

Cod liver oil and fish oil are similar, but cod liver oil has much higher levels of vitamins A and D. Many adults do not meet the RDA for Vitamin D.

Cod liver oil is effective in treatment of household burns, due to its high vitamin content, often leaving no burn-related blister.

Cod liver oil has been listed by some as an effective complementary measure for long-term treatment of Multiple Sclerosis, a sometimes disabling autoimmune disease of the human central nervous system.

In 2005, a study by researchers at the University of California found that Vitamin D may lower the risk of developing different types of cancers, halving the chances of getting breast, ovarian, and colon cancers.

Use of cod liver oil during pregnancy is associated with lower risk of Type I diabetes in the offspring. This effect was found only in mothers taking cod liver oil, not in mothers taking multivitamin supplements. It should be noted that cod liver oil contains unsafe amounts of vitamin A for pregnant women. Cod liver oil taken by nursing mothers improves the breast milk by increasing the amount of fatty acids, which promotes brain development, and the amount of vitamin A, which helps prevent infections, but the level of vitamin D is unchanged.

Adverse effects

Because cod liver oil has a very high level of Vitamin A, it is possible to exceed the Recommended Dietary Allowance (RDA) of vitamin A. Vitamin A accumulates in body fat, and can reach harmful levels sufficient to cause hypervitaminosis A. Pregnant women should not take cod liver oil due to the high amount of Vitamin A, which, in high doses is shown to cause birth defects.

The risks of hypervitaminosis and of exposure to environmental toxins such as mercury, polychlorinated biphenyls, dioxins, and other contaminants, are reduced when purification processes are applied to produce refined fish-oil products, which consequently contain raised levels of omega-3 fatty acids, such as EPA and DHA.

A high intake of cod liver oil by pregnant women is associated with a nearly five-fold increased risk of gestational hypertension, although this study did not control for mercury, which can be present in harmful amounts in fish and which is another cause of hypertension.

Some urge caution when taking cod liver oil and other fish-based supplements since they may contain elevated levels of toxins such as mercury and PCBs found in fish. Some supplement companies regularly test cod liver oil for purity, while others do not. Ultimately the specific concerns of mercury in cod liver oil are generally not justified. Consumerlab.com tested 44 fish and cod liver oil supplements and found that all were free of detectable levels of mercury.

Other uses

In Newfoundland, cod liver oil was sometimes used as the liquid base for traditional red ochre paint, the coating of choice for use on outbuildings and work buildings associated with the cod fishery.

See also

• Vitamin A overdose
• Shark liver oil

References