Cod liver oil
- This article is about the fish oil; for the traditional Newfoundland song, see "Cod Liver Oil (song)".
Cod liver oil is a nutritional supplement derived from liver of cod fish. As with most fish oils, it has high levels of the omega-3 fatty acids, EPA and 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.
Cod liver oil was traditionally manufactured by filling a wooden barrel with fresh cod livers and seawater and allowing the mixture to ferment for up to a year before removing the oil. Modern cod liver oil is made by cooking the whole cod body tissues of fatty fish during the manufacture of fish meal.
Cod liver oil is widely taken to ease the pain and joint stiffness associated with arthritis. It may have a positive effect on heart, bone, as well as helping to repair wounded skin, hair, nails, and teeth.
Cod liver oil and fish oil are similar, but cod liver oil has higher levels of vitamins A and D. According to the USDA, a tablespoon of cod liver oil (13.6 g) contains 4080 μg of retinol (vitamin A) and 34 μg of vitamin D. The Recommended Dietary Allowance of vitamin A is 900 μg per day for adult men and 700 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.
Use of cod liver oil during pregnancy is associated with lower risk of Type I diabetes in the offspring. (although see adverse effects below). This effect was found only in mothers taking cod liver oil, not in mothers taking multivitamin supplements. 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.
A Norwegian study of more than 68,000 women reported that female cancer patients who took daily cod-liver oil supplements had significantly reduced mortality (25% for all cancers, 45% for lung cancer) compared to women who did not take such supplements.
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 body fat, 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. High doses of synthetic vitamin A (retinoids) have been shown to cause birth defects. 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 hypervitaminosis and of exposure to environmental toxins such as mercury, polychlorinated biphenyls (PCBs), 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 fivefold 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.
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