Many people confuse fish oil with cod liver oil. Ever since 1999, when James Donadio suggested that fish oil slows the progression of a kidney disorder called IgA nephropathy, many kidney patients have taken fish oil. Cod liver oil has no such track record. It has no benefits at all for the kidneys of healthy people and can be downright dangerous for kidney patients.
Cod Liver Oil
Unlike fish oil, which is made from the bodies of whole fish, cod liver oil is made from the livers of codfish. Nutritionally, it is very different from fish oil. One tablespoon of cod liver oil has 13,600 IU of vitamin A and 1,360 IU of vitamin D. This is 582 percent of the daily value of vitamin A for women and 340 percent the daily value of vitamin D.
Vitamin A
The kidneys of patients with advanced kidney disease are unable to remove excess vitamin A from the blood. Writing for the January 2011 issue of "Journal of Renal Nutrition," Handelman and Levin note that levels of vitamin A in kidney patients typically are quite high. The additional vitamin A in cod liver oil could easily cause vitamin A toxicity.
Relative Risk
The risk of vitamin A toxicity, also called hypervitaminosis A, caused by cod liver oil is even higher if it is taken in large doses. Kidney patients often take 12 g of fish oil per day, especially if they are trying to get the 1.9 g of eicosapentanoic acid and 1.4 g of docosahexanoic acid recommended by Donadio in his 1999 paper. Under these circumstances, confusing cod liver oil and fish oil could cause liver damage, hemorrhage and coma.
Other Risks
Since cod liver oil is made from the liver, contamination by polychlorinated biphenyls and other toxic wastes and pollutants is a concern because such substances tend to accrue in that organ. If you must take cod liver oil, make sure you purchase it from a reputable source to minimize this problem. If necessary, consider reviewing reports from a testing lab or consumer protection agency.
References
- "Journal of Renal Nutrition;" Guidelines for Vitamin Supplements in Chronic Kidney Disease Patients: What Is the Evidence?; G.J. Handelman and N.W. Levin; January 2011
- U.S. Department of Agriculture: Cod Liver Oil
- Foundation for IgA Nephropathy: Fish Oil
- "Journal of the American Society of Nephrology;" The Long-Term Outcome of Patients with IgA Nephropathy Treated with Fish Oil in a Controlled Trial; James V. Donadio, MD, et al.; August 1999
- Linus Pauling Institute; Vitamin A; Jane Higdon, Ph.D.; December 2003
- Berkeley Wellness Letter: Cod Liver Oil
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