While cod liver oil comes from a fish and is often casually referred to as fish oil, don't confuse products labeled "fish oil" with those labeled "cod liver oil." These are two very different supplements with very different benefits and risks. Kidney patients should steer clear of cod liver oil because this product can cause vitamin toxicity.
Cod Liver Oil
Cod liver oil comes from the livers of cod fish. Parents in the first half of the 20th century often warned their kids that they'd have to take cod liver oil if they were on the verge of getting sick. It is very unlikely that this had any benefit. As of 2011, most people who take cod liver oil are older adults who suffer from osteoarthritis. Available in both capsules and liquids, it is very high in vitamins A and D.
Fish Oil
Fish oil, on the other hand, is made from oil from the bodies of whole fish. The Mayo Clinic rates it a "B" or better in the treatment of hypertension, cardiovascular disease, rheumatoid arthritis and in the prevention of cyclosporine toxicity. While the benefit of fish oil in kidney patients is less certain, patients with chronic kidney disease often take large doses in the hope that it will retard the progression of kidney disease.
Warning - Vitamin A
The nutritional needs of kidney patients are very different from healthy people. For example, serum levels of potassium, phosphorus and vitamin A can be dangerously high in patients with advanced disease. Cod liver oil, with its high vitamin A content, can cause toxicity in these patients, especially if taken in the large doses associated with fish oil.
Contaminants
The Berkeley Wellness Guide to Supplements cautions that contamination with polychlorinated byphenyls, also called PCBs, may be a concern for people who take cod liver oil because toxins accumulate in the livers of fish. This is not a problem with regular fish oil because these toxins concentrate in the fish's liver, not the body oil.
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