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Diet & Health : Nutrition Last Updated: Apr 20, 2011 - 9:38:09 AM

Cod liver oil could do more harm than good
By David Liu Ph.D.
Dec 10, 2008 - 9:34:48 AM

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Wednesday Dec. 10, 2008 ( -- Lack of vitamin D is associated with a wide range of conditions including respiratory infections.   Studies have showed intake of high doses of vitamin D reduced risk of respiratory infections drastically.   There is some evidence suggesting that taking high doses of vitamin D may be more effective than flu vaccine at preventing colds and flu.


Cod liver oil has been popular in the West because it provides three major nutrients, omega-3 fatty acids, vitamin D and vitamin A.   Many parents give it to their children.  But many people, even some nutritionists, may not know that today’s cod liver oil is actually not as good as thought.


John Cannell, MD and more than a dozen of other vitamin D experts questioned the value of cod liver oil in their commentary published in a recent issue of Annals of Otology, Rhinology and Laryngology. They were concerned that cod liver oil contains too little vitamin D and too much vitamin A.


The recommended daily allowance (RDA) for vitamin A is 2000 IU for children at 9 to 13, and 2000 IU for people at 14 and older.   The RDA for Vitamin D is 200 IU for all people under 50 and 400   IU for people between 50 and 75 and 600 IU for those older than 75.


Many vitamin D experts agree that the RDA for vitamin D is way too low.   According to Dr. John Cannell and his colleagues, 1,000 IU daily may be needed for a 25-pound child.


According to the Agricultural Research Services, a research arm of the U.S. Department of Agriculture, 100 grams of cod liver oil contain 100,000 IU of vitamin A and 10,000 IU of vitamin D.   That is, one teaspoon (5 ml) may contain 5,000 IU vitamin A and 500 IU vitamin D.      


What does the ratio means? Dr. Cannell and his colleagues suggested that the high amount of vitamin A and low amount of vitamin D together could do more harm than good. Remember that this data come from unprocessed cod liver oil and the ratio of vitamin A to D in cod liver oil sold today can be much worse because vitamin D gets lost during the processing of cod liver oil.


Vitamin A in cod liver oil by itself may cause toxicity.   The body does not have much control over high intake of vitamin A from cod liver oil meaning that it is easy to render a toxic effect if you take too much of vitamin A.   Because of this, many nutritionists say it is better to take beta-carotene, which can be converted into vitamin A and never exert any toxicity in a dose of up to 20,000 IU a day.   Actually you do not have to take any supplement at all if you use lots of fruits and vegetables in your diet.


Low serum vitamin D has been known to cause a wide array of diseases and health conditions.     Some cod liver oil contains as little as 20 IU per teaspoon.   Even if you take the unprocessed cod liver oil and you get 500 IU of vitamin D per teaspoon, chances are good that you are still vitamin D deficient.


Some cod liver oil contains a relative high level of vitamin D.   The manufacturers are likely to add vitamin D back to cod liver oil to compensate the loss due to the processing.   Still the ratio of vitamin A to D is too high.


One more thing bad about cod liver oil is when vitamin A and vitamin D are used together, the benefit from the already low intake of vitamin D may be further reduced because of the presence of vitamin A. Cannell and colleagues said vitamin A interferes with the functionality of vitamin D.  Large amounts of vitamin A could actually make the tiny intake of vitamin D ineffective.   Because of this, Dr. Cannell recommended that vitamin A supplements and cod liver oil should not be taken, particularly by pregnant women.

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