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The cod liver oil controversy

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Ever since Dr. Cannell (Vitamin D Council) said cod liver oil shouldn't be taken, scientists & doctors are duking it out on both sides of the issue.

Who would have thought that cod liver oil could be controversial? After all, our grandparents were raised on cod liver oil, and it was given to all children like a religion prior to the 1950s with no apparent ill effects, and lots of good effects ... But when Dr. Mercola, who has a readership of over a million people, sided with Dr. Cannell, and told his subscribers he was no longer recommending cod liver oil, a few readers asked me what I thought of the whole controversy. So, here is my two cents worth. Please remember that I am neither a doctor, nor a scientist - just a health geek that reads a lot and comes to my own conclusions, so take what I say with a good dose of skepticism, just as I think one should of what anyone tells you, including your doctor and your government. Do your own research and make up your own mind about what feels right for you.

Cod liver oil is not only a fabulous source of omega 3 fatty acids, important
for brain function and cardiovascular health, but also a good source of vitamin D and A, especially important in the winter months in parts of the world where there is little sun, and vitamin D deficiency is common. If your shadow is longer than you are when you are in the sun, your body can't make vitamin D.  Because there are not many foods that contain much vitamin D, and people have been frightened away from precisely those foods like lard, liver, eggs etc. due to the mistaken belief that cholesterol and saturated fat are unhealthy, cod liver oil would seem to be an excellent choice in the winter, especially since synthetic vitamin D supplements are less reliable than a food for obtaining health benefits. It should also be noted that the Inuit live in darkness for many months of the year - no sun available at all - and they traditionally relied on food sources for their vitamin D - seal blubber and lots of fatty fish. They did not appear to have any signs of vitamin D deficiency. I would imagine that because we are all biochemically different, we would all require
different amounts of vitamin D and A to be healthy.  There is certainly some indication of that concept based on this study of calcium absorption in Inuit children.

So, what's the problem?  In a nutshell, some cod liver oils are very high in vitamin A in relation to vitamin D, and vitamin A in high doses is not only toxic, but according to Dr. Cannell can actually interfere with the utilization of vitamin D. So by taking in too much vitamin A, according to Dr. Cannell, it can inhibit the binding of Vitamin D to your DNA, thereby affecting the expression of those
genes that are regulated by Vitamin D.  The argument is that in the western world, we get a lot of vitamin A in our diet, and there is no reason to risk supplementation with extra vitamin A, especially at the high levels often found in cod liver oil.  Because both vitamin A and D are fat soluble rather than water soluble, we do not excrete the excess vitamin A and D that we consume, and hence the toxicity danger.  Both vitamin A and D are  tightly controlled by the body, and converted to the active form only as needed in order to reduce the chance of toxicity.  But because the vitamin A in cod liver oil comes in its active form, retinol, it bypasses the body's control mechanism, increasing the chance of toxicity.  In the developing world, vitamin A toxicity is unlikely to be an issue, but in the developed world, some argue that vitamin A toxicity is more common than one would think.

However, according the research of Weston A Price, vitamin A is NOT toxic except in the case of vitamin D deficiency. In nature, foods that contain vitamin D also contain vitamin A, because they work synergistically. Seal oil, a staple of the Inuit diet has far higher levels of vitamin A than cod liver oil. In fact, Dr. Price found that many traditional cultures consumed vitamin A in far greater amounts than we do in current times. The Weston A Price Foundation does not agree at all that there is rampant vitamin A toxicity in the western world, due not only to the general population's fear of saturated fat, but also due to the fact that many (those with thyroid, liver problems, diabetes, children and babies) have trouble converting carotenoids in vegetables into vitamin A. Until there is a similar medical test for vitamin A levels as is available for vitamin D, I guess we won't know who is right. The Weston A Price Foundation also disagrees with Cannell's statement that high levels of vitamin A will interfere with vitamin D regulated gene transcription, stating that  "researchers from Spain recently showed that vitamin D can only effectively activate target genes when its partner receptor is activated by vitamin A". To understand the biochemistry of the interaction between vitamin A and D in more detail, click here, or here for the Spanish study. The key, according to the Weston A Price Foundation, is that the body can use natural food sources of vitamin A and D, as they are packaged in appropriate ratios.  Supplementation is problematic, because frequently not only are those ratios are out of whack, but also synthetic vitamin A and D are toxic.  Once again, rely on food for nutrition, not supplements.

So, what does this all mean for cod liver oil? The problem is that in the modern cleaning and processing of cod liver oil, the vitamins are frequently removed, and then synthetic vitamins are added back in, and not in the same ratios that were naturally in the oil to begin with. Cod liver oil is frequently being turned into a supplement rather than the food it originally was. So often one sees ratios of vitamin A to D of 100:1, which is crazy high in vitamin A with respect to D.  Ratios should be in the range of 10:1 or less, and thankfully there are many natural cod liver oils on the market that meet that requirement.

So rather than throwing the baby out with the bathwater and missing out on the omega 3s and vitamins in cod liver oil, I think we simply need to be very picky about what cod liver oil we choose to use.  Look for naturally occurring vitamin A and D, and make sure the ratio is 10:1 or less. Fermented cod liver oil is probably the best, but is hard to get in Canada at least.   Carlson's is readily available in my neck of the woods, and has 700 to 1200IU vitamin A to 400IU vitamin D in the liquid, a good ratio, and well below the recommended daily allowance of 10,000IU vitamin A a day. Other good online sources include Garden of Life regular dose, Nordic Naturals High Vitamin D cod liver oil, Radiant Life High Vitamin Cod Liver Oil, Wolf River Naturals, and Dr. Ron's High Vitamin Blue Ice.

Remember that fish oils as well as fish liver oils, like vegetable oils, are mostly polyunsaturated fatty acids  and therefore very prone to oxidation, and need to be kept in the fridge in order to prevent rancidity (vegetable oil exceptions are olive and coconut oils which are mostly monounsaturated and saturated fatty acids respectively). Pay attention to expiry dates. Furthermore, this vitamin controversy does not apply to regular fish or krill oils that are used for omega 3 supplementation, as these oils do not have vitamin A nor D in them.

For those of you in the Vancouver area, I will be presenting a two-hour nutrition seminar on Tuesday Jan. 27th from 7 to 9pm. For more information and how to register, contact me and I will forward you the poster and registration information. Hope to see you there!

If you want to search for other posts by title or by topic, go to

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Cannell, John MD et al. Cod Liver Oil, Vitamin A Toxicity, Frequent Respiratory Infections, and the Vitamin D Deficiency Epidemic Ann Otol Rhinol Laryngol 2008;117:864-870.

Cannell, John MD et al. Vitamin D Council Newsletter

Mercola, Joseph MD Important Cod Liver Oil Update Dec. 23, 2008.

Fallon, Sally Update on Cod Liver Oil, Dec. 2008 Weston A Price Foundation

Fallon, Sally Information update on cod liver oil Weston A Price Foundation, Dec. 2008

Wetsel, David Cod Liver Oil -- Notes on the Manufacture of Our Most Important Dietary Supplement Weston A Price Foundation 2006

Fallon, Sally, and Enig, Mary PhD Vitamin A, Vitamin D and Cod Liver Oil: Some Clarifications Weston A Price Foundation, 2007

Sánchez-Martínez R et al. The retinoid X receptor ligand restores defective signalling by the vitamin D receptor. EMBO Rep. 2006 Oct;7(10):1030-4. Epub 2006 Aug 25.

Ruth Sánchez-Martínez et al. Vitamin D-Dependent Recruitment of Corepressors to Vitamin D/Retinoid X Receptor Heterodimers Mol Cell Biol. 2008 June; 28(11): 3817–3829.

Online at the Weston A Price Foundation Cod Liver Oil

Caire-Juvera G et al. Vitamin A and retinol intakes and the risk of fractures among participants of the Women's Health Initiative Observational Study. Am J Clin Nutr. 2009 Jan;89(1):323-30. Epub 2008 Dec 3.

Lam HS et al. Risk of vitamin A toxicity from candy-like chewable vitamin supplements for children. Pediatrics. 2006 Aug;118(2):820-4.

Myhre, et al., Water-miscible, emulsified, and solid forms of retinol supplements are more toxic than oil-based preparations, Am J Clin Nutr, 78 (2003) 1152-9.

Brustad M et al. Vitamin D status in a rural population of northern Norway with high fish liver consumption. Public Health Nutr. 2004 Sep;7(6):783-9.

Aburto, et al., "The influence of Vitamin A on the Utilization and Amelioration of Toxicity of Cholecalciferol, 25-Hydroxycholecalciferol, and 1,25-Dihydroxycholecalciferol in Young Broiler Chickens," Poultry Science 77 (1998) 570-577.

Metz, et al., The Interaction of Dietary Vitamin A and Vitamin D Related to Skeletal Development in the Turkey Poult J. Nutr. 115 (1985) 929-935.

Heaney, Robert P., "The Vitamin D requirement in health and disease," Journal of Steroid Biochemistry & Molecular Biology, 97 (2005) 13-19.

Aburto and Britton, Effects of Different Levels of Vitamins A and E on the Utilization of Cholecalciferol by Broiler Chickens Poultry Science 77 (1998) 570-577.

Copyright 2009 Vreni Gurd

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Comments (19)

Submitted by Anonymous (not verified) on Mon, 02/16/2009 - 8:19pm.

I started seeing a dr last year who recommened that I take cod liver oil by Carlsons becuase it's one of the better brands on the market. I had been taking it faithfully since last May up until about a month or so ago, due to the fact that I amhaving a of hair loss and I did read on the back of a liquid brand (I was using the gel caps) that too much could result in hair loss. I need to know if there is any truth to this. My hair was growing and doing fine and then a few months ago I started seeing lots on the floor and in the sink and I slowed down my intake.

Submitted by Fatty Liver Diet (not verified) on Wed, 10/06/2010 - 8:47pm.

What is the best way to take cod liver oil? Does it come in both liquid and capsule form? I've heard it tastes horrible so I wasn't sure if it comes as a pill or only as a liquid. Is there a recommended way to take it?

Submitted by Vreni Gurd on Wed, 10/06/2010 - 9:05pm.


I like Carlson's Cod Liver Oil, as the ratio of vit d and A is good.

Comes in lemon flavour, and in capsules or liquid.


Vreni Gurd BPHE


Health and Vitality Coach

Corrective Exercise Specialist

Certified Integrated Somatic Therapist (INT)

Metabolic Typing Advisor


Submitted by Gil (not verified) on Tue, 11/23/2010 - 2:27pm.

I am always weary when I buy Fish oil. You never know what you will get. I personally buy the animal Omega. From what i have read it is really pure. Do you know how to tell what is pure?

#5: How
Submitted by hair treatment for hair loss (not verified) on Thu, 11/25/2010 - 2:27am.

How did you know about this cod liver oil? Thanks!

Submitted by hair loss products (not verified) on Mon, 11/29/2010 - 6:53pm.

Cod liver oil really helps?

Submitted by hoodia gordonii plus (not verified) on Sun, 03/20/2011 - 10:59am.

My mother used to gave me COD liver oil since I was a kid but stopped taking in when I was in college. Now I'm planning to do the same with my son, anyone where can recommend a good brand of COD liver oil?

Submitted by Vreni Gurd on Sun, 03/20/2011 - 9:58pm.

Vreni Gurd BPHE


Health and Vitality Coach

Corrective Exercise Specialist

Certified Integrated Somatic Therapist (INT)

Metabolic Typing Advisor


Submitted by fattyliver on Sat, 05/07/2011 - 7:41pm.

I have been taking cod liver oil for most of my life. I am not worried about the vitamin A toxicity concern. I am not overweight and lead a very active lifestyle.

Submitted by Rob Johnson (not verified) on Wed, 05/11/2011 - 5:56pm.

I have heard that hair loss can happen when taking cod liver oil. I am 38 now, and still have a full head of hair. I have been taking cod for a long time now.

Submitted by vitamin supplements (not verified) on Mon, 06/06/2011 - 8:24am.

hmm very informative post...Thanks for sharing it...

Submitted by turns2green (not verified) on Sun, 07/17/2011 - 5:54pm.

On the packaging for organic carrots I bought recently it says one carrot has about 270% of your daily Vitamin A value. Either eating one carrot will overload you with Vitamin A or the daily intake values for vitamin A are way off?

Submitted by Vreni Gurd on Sun, 07/17/2011 - 6:37pm.

Hi turns,

Usually there is very little issue with vitamin toxicity when it comes in food.  Food delivers its nutrients in a food-complex that the body understands.  But when we take a beta caroteen pill or a vitamin A pill, we have taken away everything else that the body thinks should come with vitamin A, and so it has to work hard plucking this enzyme and that vitamin etc. to recreate the complex before it can use it.  Scientists keep trying to look at things in their separate pieces and make definitions of RDAs based on the pieces rather than looking at food complexes and whole food.  So maybe the daily intake values for separate vitamins are really not important. What is important is to eat a wide variety of foods in order to ensure you get the vitamin complexes you need to be healthy. What do you think?

With cod liver oil, where instead of simply taking out any impurities, they also strip the oil of the vitamins, and then put them back in in the ratios they choose.  Therefore cod liver oils are usually quite processed.  If the A and D were simply left in the oil in its natural state, there would be no toxicity problem. 

Vreni Gurd BPHE
Health and Vitality Coach

Corrective Exercise Specialist

Certified Integrated Somatic Therapist (INT)

Metabolic Typing Advisor


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Submitted by Mike F. on Fri, 05/25/2012 - 2:20pm.


Thank you for taking the time to write this article. It was a great read!

I just discovered the works of Weston A. Price a few weeks ago and have ordered his book Nutrition and Physical Degeneration to read. Based on his book reviews and WAP topics I've read online I've come to understand that two crucial things he highly stresses getting into one's diet are high vitamin butter oil and cod liver oil.

I wholeheartedly agree with your statement to "rely on food for nutrition, not supplements." To me, this begs the question of why not just eat high-quality, grass-fed butter and actual cod liver (from a can) rather than debate which synthetic forms of these two items to take. Logically, it makes more sense to me to go to the actual source to obtain the best benefits of health, rather than rely on a manufacturer to produce and mimic elements of food that are already found in nature, in the right ratios (such as A to D) to boot!

I would very much appreciate hearing your thoughts on this matter. Thanks in advance for taking the time to answer!

Mike F.

Submitted by r4i gold 3ds (not verified) on Mon, 03/18/2013 - 8:27pm.

Can you type long blog posts on the PS3 web browser?

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