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Cod liver oil is a poison and the research has always said so

Warning:  This post may be a bit painful.  We were all very much deceived into believing the myth of cod liver oil being a "health food".  I hope this post wakes people up to this health-damaging product.  Please share this post with anyone you know who is still under the false spell/myth that cod liver oil (CLO) is “good for them”, and particularly to help them stop giving it to their children and starting them on a potential lifetime of poor health.

First, you may want to use the little search box above the blog-forum to search this site for “cod liver oil”.  If you don’t believe the research below, please read the anecdotes from other people (especially other well-meaning mothers) who took cod liver oil and/or gave it to their children and slowly watched all of their health decline.  Quite the opposite of what they were promised by the pseudo-nutrition gurus preaching ”appeal to nature” (if it’s natural, it must be good and safe) and ”appeal to tradition” (if people in the past used it, like Weston Price, it must be better than what we’re doing now) fallacies.

Let’s go as far back as possible and note the first “coincidental correlation” with cod liver oil and disease.  No, I don’t believe in coincidences.  Note how many of the following observations are from the 1930s.

Introduction of oral vitamin D supplementation and the rise of the allergy pandemic

English cities in 1880 were characterized by an extremely high rickets prevalence, the beginning of commercial cod liver oil production, and the near absence of any allergic diseases. By 1930 hay fever prevalence had risen to about 3% in English-speaking countries where cod liver oil was preferentially used for the treatment of rickets. In 1980 vitamin D was used nation-wide in all industrialized countries as supplement to industrial baby food, thus eradicating nearly all cases of rickets. At the same time the allergy prevalence reached an all-time high, affecting about 30% of the population.

Is it Vitamin A?  Is it Vitamin D?  CLO has them both!  They are both problems.  I’m trying to stick to CLO as a single package in this post.

Regarding the idea that because cod liver oil is “natural”, it must be safe, right?  What happened to dogs when they were fed CLO for 8-20 months?  They got heart disease as shown on ECGs:

The Appearance of the Electrocardiogram in Heart lesions produced by Cod liver Oil Treatment.

Eight dogs treated for from 8 to 20 months with cod liver oil in a dose 0.1‐l‐(5) cc. of oil per kg. bodyweight per day, show obvious alterations of their electrocardiogram and degenerative heart lesions of the usual type.

As may be expected from the comparatively small dose of oil, the alterations of the Ecg. are rather small, mainly consisting of alterations in the size and direction of the T‐summit and prolongations of the times of the curve. Clear changes of these kinds occur in all the cases and are rather uniform. Curves such as those occurring in bundle branch block are indicated only in two cases, one of which received the greatest dose of oil administered.

There is certain evidence that even so small a dose as 0.1 cc. of oil per kg. bodyweight per day is injurious to the heart of the dog.

The alterations of the Ecg. may occur within 2–4 months after the commencement of the treatment.

There are some key words that are used that make it obvious that the above researchers KNEW about cod liver oil's negative effects:  "obvious", "usual", "expected", "clear", "rather uniform", "certain evidence".  Isn't it amazing how this was pedestrian to the scientists back then, yet everyone is so ignorant of this science now?

Did the great Weston A. Price himself have any concerns about cod liver oil being toxic, considering that it is his past work that so many CLO pushers today lean on?  Yes, he absolutely did.  From 1932:

Control of Dental Caries and Some Associated Degenerative Processes Through Reinforcement of the Diet with Special Activators by Weston A. Price D.D.S., M.S., F.A.C.D.

”I have frequently had mothers bring this question to me as a serious nutritional problem with their children. They had desired to do all they possibly could for their children and, in their efforts, had tried to follow the directions on the bottle or as otherwise provided, which often meant large doses of cod liver oil. They have reported to me the difficulty they had in combating the rebellion of their children against the use of cod liver oil, which may have been in part a reaction of self-preservation. Many of the children were reported to regurgitate the oil when it was forced down. Since it has been demonstrated that only the oil that is utilized contributes to the well-being of the human being or animal, it can readily be anticipated that compulsion to take such a toxic product could be very injurious.

If kids are fighting back tooth and nail to avoid eating something, do you think that they might instinctually know what they are doing?  If they are vomiting something back up, do you think their BODY is outright rejecting that thing being forced on it?  Have you ever noticed how strongly kids will reject brightly colored vegetables, in favor of white (often starchy) foods?  Have you ever noticed how hard it is to get kids to eat liver?  Do you think G-d/Nature had a REASON for doing these things?  All these things are generally high in Poison/”Vitamin A”!!!

More from Dr. Price, from the book Nourishing Traditions, page 391 (I’m absolutely NOT recommending this book, just quoting from it):

Cod liver oil can be given in moderate doses without injury and to great advantage.  Seldom, however, should the child be given more than one teaspoonful a day for extended periods, because of toxic effects that often develop.

– Weston Price DDS, Letter to His Nieces and Nephews, 1934

Extended periods of taking cod liver oil causing toxic effects to often develop?  Sounds like a slow case of poisoning to me!  Thanks for clearing that up, Dr. Price.  Too bad nearly everyone (including myself, in my younger years) simply ignored those massively important parts of your legacy and paid a price for it. (pun intended)

Wait, there’s another paper from 1934 (when Price wrote that letter above) that discusses these “toxic effects” of cod liver oil?  Yes, there is.


Cod liver oil and its concentrated forms have played an important rôle in the nutrition of infants. But like many other food substances they have at times been responsible for “upsets” in the allergic child, manifesting themselves in the form of vomiting, diarrhea, urticaria, eczema and asthma, or in a combination of these syndromes. Because of this frequent complication we have been searching for a product which could be given to children sensitive to cod liver oil, whose diets, for allergic reasons, have been inadequate in vitamin-containing foods. One can readily appreciate the likelihood of dental caries and the lowered resistance to infection in any child whose diet must be limited to a few foods, and who in addition is unable to tolerate cod liver oil in any form.

We wish to report the cases of four allergic children in whom, owing to the addition of cod liver oil to their diets, various types of allergic manifestations developed other than the one for which they first came seeking relief, but who manifested no untoward symptoms when carotene concentrate fortified with Vitamin D was substituted.

I’m working on getting the whole paper, I will add it here (and add the case studies to the appropriate section) once I have it.  Hey, have you noticed that there is an allergy and asthma epidemic in the “civilized world” these days, particularly in the kids?  Maybe you can start putting this all together too.

This next paper will take a while to unpack, and it's very important, from 1934:


Numerous experiments have shown that therapeutic doses of cod-liver oil cause toxic effects and organic changes of a regressive type.

"Numerous" means multiple.

"Therapeutic doses" means quantities commonly given in the hopes of treating a disease or condition.

"Toxic effects", I hope I don't have to explain this one.

"Organic changes of a regressive type" means changes related to returning to a former or less developed state (regressive) in the tissues of the test animals.

That one sentence is full of bad implications.

Agduhr (1) demonstrated that cats and dogs showed no sign of heat when doses of 1 cc. to 5 cc. of cod-liver oil per kg./day were added to the basal diet beginning at the age of one month and continuing for one year. The number of red blood corpuscles was decreased simultaneously with a fairly steady increase of the relative haemoglobin value. The spleen was abundantly supplied with blood pigments, a sign that the disintegration of red blood corpuscles was above the normal. Histological changes in different organs chiefly of a regressive nature were found but no mention was made of the thyroid gland. The weight curves of the mice as well as the microscopical examination of their organs showed many disturbing alterations.

Summary of the above:

  • "No sign of heat" means that the dogs and cats were made INFERTILE.
  • The decrease in red blood cells (corpuscles) and the increase in blood pigments (hemoglobin) in the spleen means that a hemolytic anemia was induced.
  • Hopefully you understand that "disturbing alterations" of the organs and the microscopic level is VERY BAD.

In 1925 Slagsvvold (2) noted poisoning among cattle by cod-liver oil while rodents thrived on the same oil. Norris and Church (3) point out that the toxic effect of large doses of some cod-liver oils is not due to hypervitaminosis due to excess of vitamins A and D. Continued small doses of isoamylamine in amounts which may be found in cod-liver oil produce paralysis, convulsions, and lack of growth; the toxic effect may be prevented or cured by added yeast.

What they really showed above was that there are ADDITIONAL toxic things than only Poison/"Vitamin A" and Hormone-D in cod liver oil!

Harris and Moore (4) report that results obtained have been distinguished by a remarkable regularity in the retarding action of the vitamins A and D concentrates upon growth rates.

People give their children CLO hoping they'll grow well, while the research shows that quite the opposite is true.

Since large doses of cod-liver oil have, as a rule, been followed by a decrease in the number of red blood corpuscles and marked regressive tissue changes, it was decided to run basal metabolism determinations and to study the thyroid gland since this organ has a definite function in basal metabolism.

OK, so what did they find?

No change in basal metabolism was produced in any of the animals during the investigation. When sections of the thyroid glands were studied  at the termination of the basal metabolism tests, marked changes were noticed only in the glands of the rats that had received normal cod-liver oil. The thyroid glands were nearly depleted in acinar colloidal content. The thyroid glands of the 30 control rats showed no deviation from the normal when compared to the glands of a group of animals that had received onlv the normal basal diet.

In 27 rats that received 1 to 5 cc. cod-liver oil per kg./day a decided change was produced in the thyroid gland, namely, a depletion of the colloidal content of the acini. Three control groups of ten animals each received, respectively, corn oil, viosterol and cod-liver oil from which the vitamin A was removed by heat and oxidation. In these the thyroid was not affected.

CLO that contained Poison/"Vitamin A" = bad changes in the thyroid tissue.

CLO that had NO Poison/"Vitamin A" in it = no changes in the thyroid tissue.

So until I started writing this article, I had no idea that way back in 1941 that scientists knew that cod liver oil had been demonstrated produce MUSCULAR DYSTROPHY (lesions in the skeletal muscles) in “rabbits, guinea pigs, goats, and sheep.”  I will comment on the Vitamin E further down.


(see link for paper)

1961.  Another paper on the damaging effects of cod-liver oil, and trying to prevent the effects with Vitamin E.

Prevention of the injurious effects of excessive cod-liver oil by its fortification with vitamin E.

(see link for paper)

My big post on Vitamin E is here.  I do not believe it to be a panacea/cure-all to preventing all the problems with cod liver oil or Vitamin A, however, if done PROPERLY I do believe it can be quite helpful.  Vitamin E in supplements can be overdone, and many common Vitamin E supplements are sourced from red palm oil and/or annatto (both ASTONISHINGLY high sources of Poison/”Vitamin A” carotenoids), so this is not a subject I take lightly or give off-the-cuff recommendations for.  If I was taking a Vitamin E supplement that is a (dark) brownish or reddish color–or somewhere in between the two–if it were me, I would throw it in the garbage, as it is full of Poison/”Vitamin A”.

Moving on to asthma and allergies.

Multiple studies linking increased asthma and allergies (atopy) to cod liver oil use in CHILDREN.

Multiple studies linking increased asthma to cod liver oil use in ADULTS.

2008…Women who consumed cod liver oil as CHILDREN were found to have lower bone mineral density as 50-70 year-old ADULTS (aka BMD, used to assess progression towards osteopenia and osteoporosis).  Yet another example of how Poison/"Vitamin A" toxicity must be actively depleted and detoxed, or else the problems will follow one for their ENTIRE LIFE:

Childhood cod liver oil consumption and bone mineral density in a population-based cohort of peri- and postmenopausal women: the Nord-Trondelag Health Study.

It is not known whether childhood cod liver oil intake is related to variations in bone mineral density (BMD) or fractures in adult life. In 2001, a total of 3,052 Norway women aged 50-70 years had forearm BMD measured in a substudy of the population-based Nord-Trøndelag Health Study. Women reporting no childhood cod liver oil intake had statistically significantly higher BMD than those with any ingestion of cod liver oil. The odds ratio for low BMD (>1 standard deviation below age-specific mean) in women reporting cod liver oil intake throughout the year as compared with women with no intake was 2.3 (95% confidence interval: 1.4, 3.9), adjusted for body mass index, smoking, menopausal status, estrogen use, and current milk consumption. There were indications of a negative dose-response effect of childhood cod liver oil intake on bone.

Next, a paper from 2015 warning about cod liver oil being related to a “risk of over-consumption” (of nutrients).  Gosh, which one(s) do you think they were most concerned about?

Contribution of cod liver oil-related nutrients (vitamins A, D, E and eicosapentaenoic acid and docosahexaenoic acid) to daily nutrient intake and their associations with plasma concentrations in the EPIC-Norfolk cohort

Almost everyone in the supplement + vitamin A group reached the estimated average requirement; however, guideline levels were likely to be exceeded.
CLO-related [Cod Liver Oil-related] nutrients contribute substantially to nutrient intake, with a risk of over-consumption.

Do you see what "over-consumption" leads to from the rest of this post and the rest of this blog-forum?  A lifetime of poor health until the problem is fixed.  Moving forward.

More arthritis in those who used CLO:  Cod liver oil supplement consumption and health: cross-sectional results from the EPIC-Norfolk cohort study.

“Participants, who had prevalent heart attack or stroke, were less likely to report CLO supplements; however, self-reported arthritis was associated with increased CLO use.

Fermented cod liver oil is a WHOLE other layer of nastiness.  I like this article about the topic: Can you ferment cod liver oil?  Also, you can find Dr. Kaayla Daniels' controversial report on the analysis of "fermented" cod liver oil, or you can get a great infographic summary of it here.  (Spoiler:  you can't ferment oils/fats, and if it tastes rancid, it IS rancid).  Rancid cod liver oil is EVEN WORSE for people than "regular" cod liver oil, and haven't I shown you that the "regular" is bad enough?

On to the researched toxins in cod liver oil!  There are Persistent Organic Pollutants in cod liver oil (an example of a POP is DDT, heard anything about it maybe?), and POPs extracted from cod liver oil (!!!) have been shown to have negative effects on hormone production when applied to pig testicular cells:

Steroidogenic differential effects in neonatal porcine Leydig cells exposed to persistent organic pollutants derived from cod liver oil.

“Seafood products, including fish and fish oils, are major sources of persistent organic pollutants (POPs) which may cause endocrine disruption related to reproductive dysfunction in males. Primary porcine neonatal Leydig cells were exposed to three extracts of POPs obtained from different stages in production of cod liver oil dietary supplement, in the absence and presence of luteinizing hormone (LH). No reduced viability was observed and all POP extracts showed increased testosterone and estradiol levels in unstimulated cells and decreased testosterone and estradiol secretion in LH-stimulated cells. A decrease in central steroidogenic genes including STAR, CYP11A1, HSD3B and CYP17A1 was obtained in both culture conditions with all POP extracts. We implicate both small differences in composition and concentration of compounds as well as "old" POPs to be important for the observed steroidogenic effects.”

What are POPs?

Persistent Organic Pollutants (POPs) are organic chemical substances, that is, they are carbon-based. They possess a particular combination of physical and chemical properties such that, once released into the environment, they:

  • remain intact for exceptionally long periods of time (many years);
  • become widely distributed throughout the environment as a result of natural processes involving soil, water, and, most notably, air;
  • accumulate in the fatty tissue of living organisms including humans, and are found at higher concentrations at higher levels in the food chain; and
  • are toxic to both humans and wildlife.

The Environmental Working Group (EWG) has this to say about POPs, particularly in regards to women's POP exposure during pregnancy and nursing:

Everyone knows that women eat – and often crave – different foods when they’re pregnant. But an Environmental Working Group (EWG) analysis of government data shows that some of the things they eat more of give their babies an extra dose of toxic pollutants at the most delicate stage of life. These persistent organic pollutants (POPs) include chlordane, dieldrin, DDT, heptachlor and heptachlor epoxide, hexachlorobenzene, and toxaphene. Although men generally eat more, pound for pound, than women, this changes when women become pregnant or are nursing, when their caloric and nutrient requirements are at a lifetime high. Of the 50 foods that are most contaminated with POPs, there are 16 that women eat more of (relative to their weight) than men – including such staples as milk, hamburgers, cheese and butter. By following what her doctor recommends as a healthy diet during pregnancy and lactation, a woman will increase her intake of POPs during a time when both she and her fetus are highly vulnerable to insult from environmental toxins.

Women commonly alter their diets during pregnancy and nursing to accommodate the nutritional needs of the fetus and infant. EWG’s analysis of data on the eating habits of these women shows that this diet shift dramatically increases their own and their baby’s exposure to highly toxic pollutants like DDT, hexachlorobenzene and other POPs. This exposure is of great concern because most POPs (including DDT) disrupt the normal function of the endocrine (hormone) system in the mother and the fetus. Normal endocrine function is essential to the healthy development and functioning of many critical organ systems, particularly those involved in sexual development, reproduction, and behavior. Many scientists strongly suspect a link between fetal and neonatal exposure to POPs and the increase in a number of diseases including testicular cancer, hypospadias, endometriosis, and breast cancer. Other phenomena, such as the dramatic drop in sperm count reported in many industrialized countries, and the significantly younger age at which children now reach puberty, are also linked to POPs exposure in the scientific literature. Women should not feel guilt or take blame for the POPs in their food, and they definitely should not sacrifice nutrition to avoid POPs. Instead, the food supply should be cleaned up.

Pregnant and nursing women should be the LAST people being recommended cod liver oil based on the above.

Do you need more proof to question the cod liver oil myth?  Why didn't the cod liver oil pushers make us all aware of this research that has been around for 80 YEARS???  When we know better, we can do better.  Please share this so we can stop poisoning ourselves and our children.  Don't forget, I have a comprehensive Poison/"Vitamin A" Detox Program, along with my individualized Nutritional Restoration work, that can undo much of the damage.  It does take persistence and effort though, and the rewards in adults and children are well worth it.

Dr. Garrett Smith, the "Nutrition Detective"
Licensed Naturopathic Physician (NMD) in Arizona, home of the Love Your Liver program
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