Cod Liver Oil

Cod liver oil is derived from liver of cod. It has high levels of the omega-3 fatty acids, EPA and DHA, and very high levels of vitamin A and vitamin D.
Depending on the quality of the oil, the flavour and aroma range from a mild sardine-like flavour, to an intense and obnoxious odour 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 odour, and a bland, slightly fishy taste. Manufacturers sometimes add flavourings, such as citrus or mint essence, to cod liver oil to make it more palatable.
Cod liver oil is made by cooking cod livers with steam, and then pressing/decanting the cooked livers to extract the oil.
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 don't meet the RDA for Vitamin D.
In 2005, a study 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. 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.
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.
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 high 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.
The best way to avoid this particular problem is to buy a well-known, reliable brand of cod liver oil.