Cod liver oil is adietary supplement derived fromliver ofAtlantic cod (Gadus morhua).[1] As with mostfish oils, it contains theomega-3 fatty acidseicosapentaenoic acid (EPA) anddocosahexaenoic acid (DHA), and alsovitamin A andvitamin D.
Historically, it was given to children in the United States in the 19th century as apatent medicine and by the end of the century was being praised by doctors in medical journals.[2][3] After it wasshown, in 1920, thatvitamin D deficiency was the cause ofrickets, cod liver oil was given as a rich source of vitamin D.[4][5][6]
Cod liver oil has traditionally come in many grades. Cod liver oil for human consumption is pale and straw-colored, with a mild flavor. ScandinavianVikings produced cod liver oil by laying birch tree branches over a kettle of water, and fresh livers were laid over the branches. The water was brought to a boil and as the steam rose, the oil from the liver dripped into the water and was skimmed off. There was also a method for producing fresh raw cod liver oil.[7]
In theIndustrial Revolution, cod liver oil became popular for industrial purposes. Livers placed in barrels to rot, with the oil skimmed off over the season, was the main method for producing this oil. The resulting oil was brown and foul-tasting. In the 1800s cod liver oil became popular as a medicine and both pale and brown oils were used. Brown oils were common because they were cheaper to produce. Some doctors believed in only using the fresh pale oil, while others believed the brown oil was better. Therancid brown oils tended to cause intestinal upset.[7]
The Möller Process was invented by Peter Möller in 1850. The livers are ground with water into a slurry, then this is gently simmered until the oil rises to the top. The oil is skimmed off and purified.[8] Other methods used in modern times include the Cold Flotation Process, pressure extraction, and pressure cooking. These all require further purification steps to get a pure oil.[9]
Though similar in fatty acid composition to otherfish oils, cod liver oil has higher concentrations of vitamins A and D. According to theUnited States Department of Agriculture, atablespoon (13.6 grams or 14.8 mL) of cod liver oil contains 4,080μg ofvitamin A and 34 μg (1360 IU) ofvitamin D.[10] TheDietary Reference Intake of vitamin A is 900 μg per day for adult men and 700 μg per day for women. Thetolerable upper intake level (UL) is 3000 μg/day. For children ages 1-3 years the vitamin A RDA and UL are 300 and 600 μg/day, respectively, for children ages 4-8 years 400 and 900 μg/day. People consuming cod liver oil as a source of omega-3 fatty acids should pay attention to how much vitamin A and vitamin D this adds to their diet.[11][12]
Cod liver oil is approximately 20%omega-3 fatty acids. For this reason, cod liver oil may be beneficial insecondary prophylaxis after aheart attack.[13] Diets supplemented with cod liver oil have been demonstrated to have beneficial effects onpsoriasis,[14] and daily supplementation has been shown to be correlated with lower rates of high-severitydepression.[15]
For vitamin A, a tablespoon (13.6 g) of cod liver oil contains 136% of the adult UL, 680% of the UL for children ages 1-3 years, and 453% of the UL for children ages 4-8 years. Even a teaspoon a day (1/3 of a tablespoon) exceeds the UL for children ages 1-8 years.[10] Vitamin A accumulates in the liver, and can reach harmful levels sufficient to causehypervitaminosis A.[11]
Reducing fatty acid oxidation and environmental toxin exposure requires purification processes as part of manufacturing of refined fish oil products.[16]
InNewfoundland, cod liver oil was sometimes used as the liquid base for traditionalred ochre paint, the coating of choice for use on outbuildings and work buildings associated with the cod fishery.
InTübingen, Germany, drinking a glass of cod liver oil is the punishment for the participants in the last-place boat at the traditionalStocherkahnrennen, an annualpunting boat race.[citation needed]
Cod-liver oil was a common remedy for all diseases, and it was an unspeakably detestable thing to take.
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