Once known for its ability to prevent rickets, manufacturers of cod liver oil now tout its benefits as an alternative to fish oil as a source of omega-3 fatty acid. Some manufacturers add vitamins D or E to their cod liver oil. Cod liver oils that claim "no added vitamin D or E" do not have either added to their products. Natural cod liver oil contains omega-3 fatty acids DHA and EPA, vitamin A and vitamin D. Cod liver oil does not naturally contain vitamin E.
Manufacturing Process
The manufacturing processes today remove much of the vitamin D from cod liver oil, so some manufacturers add vitamin D back in. If the product states that no vitamin D was added, manufacturers did not replace the vitamin D lost during processing. Cod liver oil will still retain some vitamin D, however. A manufacturer that does not add back vitamin D states that their cod liver oil contains between 0 and 19 International Units of vitamin D, or 0 to 5 percent of the recommended daily allowance (RDI).
Reasons for Adding Vitamin D
Manufacturers sometimes add extra vitamin D in addition to the amount removed during processing to protect you from excess levels of vitamin A. High levels of vitamin A can cause birth defects in pregnancy as well as central nervous system disorders, liver damage and low bone density, which can lead to osteoporosis. Norwegian researchers conducting a meta-analysis of existing studies on vitamin A reported that giving vitamin D along with vitamin A reduced the toxicity of vitamin A, as reported in the December 2003 issue of the "American Journal of Clinical Nutrition."
Reasons for Adding Vitamin E
If you take fish oils, which include cod liver oil, for long periods of time, your vitamin E levels drop. For this reason, as well as to preserve the fish oil and keep it from going rancid, many--but not all--manufacturers add vitamin E to their cod liver oil. If the label states the product contains no added vitamin E, the cod liver oil will not contain any vitamin E.
Considerations
Joseph Mercola, D.O., a well-known author and critic of many standard medical practices, feels that cod liver oil contains too much vitamin A and too little vitamin D to have any positive health benefits. In his opinion, unless cod liver oil contains a significant amount of added vitamin D, cod liver oil is likely to cause vitamin A toxicity. A product with no added vitamin D will have a much higher ratio of vitamin A to vitamin D. Ask your doctor whether she feels you would benefit more from cod liver oil with or without added vitamin D or E.
References
- American Journal of Clinical Nutrition"; Water-Miscible, Emulsified, and Solid Forms of Retinol Supplements are More Toxic Than Oil-Based Preparations; Anne M Myhre, et al.; December 2003
- MayoClinic.com; Omega-3 Fatty Acids, Fish Oil, Alpha-Linolenic Acid; April 2011
- Office of Dietary Supplements: Vitamin A
- Spectrum Fish Oil: Fish Oils
- Healthier Talk; Important Cod Liver Oil Update; Joseph Mercola; December 2008
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