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Cod liver oil is a nutritional supplement derived from liver of cod fish (Gadidae). As with most fish oils, it has high levels of the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Cod liver oil also contains vitamin A and vitamin D. It has historically been taken because of its vitamin A and vitamin D content. It was once commonly given to children, because vitamin D has been shown to prevent rickets and other symptoms of vitamin D deficiency.
Contents
- Is cod liver oil rancid or healthy
- Manufacture
- Therapeutic uses
- Potential adverse effects
- Other uses
- References
Is cod liver oil rancid or healthy
Manufacture
Cod liver oil has traditionally come in many grades. Cod liver oil for human consumption is pale and straw colored, with a mild flavor. Ancient Scandinavian Vikings 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.
In the Industrial 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. However the brown oils tended to cause intestinal upset.
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.
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.
Fermented Cod Liver Oil is made using a trade secret process, but is thought to be similar to the method to produce brown oil in the 1700s and 1800s. Testing has shown FCLO has high levels of free fatty acids and a high acid value, indicating possible prolonged rancidity. However, free fatty acids and acid value may not be the correct marker to reflect the oxidation level of this product.
Therapeutic uses
Though similar in composition to fish oil, cod liver oil has higher concentrations of vitamins A and D. According to the United States Department of Agriculture, a tablespoon (4 drams or 15 ml) of cod liver oil contains 4080 μg of retinol (vitamin A) and 34 μg of vitamin D. The Dietary Reference Intake of vitamin A is 900 μg per day for adult men and 700 μg per day for women, while that for vitamin D is 15 μg per day. The "tolerable upper intake levels" are 3000 μg/day and 100 μg/day, respectively, so 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. A 300-mg soft gelatin capsule contains about 88 μg vitamin A per dose.
Rich in omega-3 fatty acids, cod liver oil may be beneficial in secondary prophylaxis after a heart attack. Diets supplemented with cod liver oil have also been demonstrated to have beneficial effects on psoriasis.
Potential adverse effects
Per tablespoon (13.6 g), cod liver oil contains 136% of the established daily tolerable upper intake level (UL) for preformed vitamin A (retinol). Vitamin A accumulates in the liver, and can reach harmful levels sufficient to cause hypervitaminosis A. Pregnant women may want to consider consulting a doctor when taking cod liver oil because of the high amount of natural forms of vitamin A such as retinol. A toxic dose of retinol (vitamin A) is around 25 000 IU/kg (see Retinol#Retinoid overdose (toxicity)), or the equivalent of about 1.25 kg of cod liver oil for a 50-kg person.
The risks of fatty acid oxidation, hypervitaminosis, and exposure to environmental toxins are reduced when purification processes are applied to produce refined fish oil products.
A high intake of cod liver oil by pregnant women is associated with a nearly fivefold increased risk of gestational hypertension. The study noted that "possibly, the amount of n-3 LCPUFA may have positive effects up to a certain level, while becoming detrimental in high doses."
Fish oil preparations that are offered with a doctor's prescription undergo the same FDA regulatory requirements as other prescription pharmaceuticals, with regard to both efficacy and safety.
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.
In Tübingen, Germany, drinking a glass of cod liver oil is the punishment for the loser at the traditional Stocherkahnrennen, a punting boat race by University groups.