While investigating the facts and fiction of vitamin A hypervitaminosis, I found myself able to confirm with published scientific evidence why one should NEVER eat bear or seal liver. By never I mean never-ever, even if facing starvation somewhere far away from any civilization. Tempting as it is to learn how people discovered this, I ended-up digging for scientific information published nearly 75 years ago, in 1943, by Drs. Rodahl and Moore of the Dunn Nutritional Laboratory of the University of Cambridge, England.
I found it easier than I thought, free of charge, in the archives of the Biochemical Journal edited for the Biochemical Society by Cambridge University Press. One would surely agree: top trusted evidence.
The story that lays behind this scientific report relied on the longtime knowledge passed from one Inuit, Yupik, or Aleut generation to another, confirmed by arctic travelers, and recently by many fellow Canadians, that polar-bear liver is poisonous if ingested by either men or dogs. Apparently, this knowledge was transmitted by word of mouth since the 16th century. As early as 1861 J. Richardson – a story teller and explorer himself – put the story in writing and published it in his famous work Polar Regions. His writings describe how members of an arctic expedition in 1596 – an expedition led by Barentzoon and originally headed to Novaya Zembla – eat polar-bear liver and became ill. “In three cases the illness was severe, with loss of skin from head to foot“, Richardson wrote and was recounted in the later published article by Rodahl & Moore. Around the same time in history, when Richardson was publishing Polar Regions, E.K. Kane published a historical report entitled Arctic Exploration in the Years 1853-1855. Apparently Kane experimented with bear liver and found the poisoning incidence to be inconsistent. He did mention two trip instances when everyone became ill after eating polar-bear liver, but also mentioned other instances when nothing happened.
Here I can only agree with you that polar-bear liver must have been really yummy if people would simply not give up eating it! I mean, once you kill a polar-bear, the meat should satisfy an arctic expedition for a long-enough time. Did they really-really-really have to eat the bear liver too?! For instance, I know that red mushrooms are poisonous. I don’t care how hungry I’d be, I just know that they would kill me – so I’m not going to touch them!! Golly, what was so difficult to understand?? That’s polar bear liver being poisonous was known since 1596! Was a bear liver feast so tempting that some adventurous culinary geeks had to “experiment” eating it to validate that it was or not really poisonous? I guess it must have been! It was a similar experiment that surely happened with tomatoes as well, centuries ago people thought they were poisonous until some adventurous culinary geeks experimented…
Most recently for Rodahl and Moore, a three year long English expedition heading to Franz Joseph Land (1894-1897) offered the opportunity to feast on polar-bear liver and they experienced the same: all got ill. Fifteen years later, the story repeats itself. We are in the grace year 1913 and this time the members of the expedition decided to stew liver with bear heart and kidneys. A total of 19 people got sick. Luckily – if one could even say that! – the more recent the facts, the more details reached us. Reportedly, two of the victims became ill in a few hours, while all the others got sick over night.
“The symptoms described were drowsiness, sluggishness, irritability or irresistible desire to sleep, and severe headache and vomiting. During the second 24 hours, the skin of 10 out of 19 of the patients began to peel around the mouth, beginning in spots and gradually spreading over larger areas. In some cases the peeling was confined to the face, but in several it was general. J. Lindhard also described three other cases in which the skin peeled from head to foot after eating bear liver”.
In 1924, a Norwegian explorer – F. Nansen – shared that eating small portions of bear liver in two instances had no consequences. In my humble opinion, humans do have an itch and unstoppable temptation to ingest things they know to be dangerous for them! However, crazy or not, Nansen’s adventurous diet enabled for the first time a hypothesis. Potentially the poisonous effect had something to do with the amount of bear liver eaten at once. It must have been something in the bear liver that, if consumed in smaller amounts, was perfectly fine for humans. Trying to reenact in my mind the thinking of some explorers back then, I can only say “well, if the bear lives with that liver, we should be able to live too…“. Indeed, the bear was 3-5 times the size of an adult man. At that size the bear could live happily with his liver. Just saying…
Knowing this, here we are in 1940 when the history repeated itself AGAIN. J. Doutt reports more cases of poisoning after eating polar-bear liver. The news made it to the Dunn Nutritional Laboratory at the University of Cambridge and triggered a scientific expedition to the North-East of Greenland later that year. This time the scientists collected polar-bear livers from a 2-year old female, a 4-year old male and a third bear whose age was not indicated, with the clear intent to determine the toxic substance causing the ill effects reported time and again throughout the previous 350 years. For comparison, they also brought back a seal liver from a species of seals named Phoca barbata. This is what Rodahl and Moore reported:
“On chemical and biological examination these specimens were found to be very rich in vitamin A, as also was a specimen of liver from P. barbata. It seems probable that this high concentration of vitamin A is the cause of toxicity, and that the ingestion of more than small amounts of liver leads to hypervitaminosis A.”
I could go over the techniques that led them to these findings, but I will spare you the headache. In brief: the research is sound, accurate and trusted by the peer-review of the Biochemical Journal. Beyond of a doubt, their data indicates that the poisoning must have been due to hypervitaminosis A. The authors describe that both the liver of the 2-year old female and the one of the 4-year old male contained 18,000IU/g vitamin A. The third bear liver specimen contained 13,000IU/g vitamin A. The only seal liver specimen also contained 13,000IU/g vitamin A.
As a scientist, I can tell you that this is not particularly impossible. Vitamin A is stored in the liver. If it gets absorbed (and it does!), unless is utilized by the body immediately, it will be stored in the liver. If we consider that the highest vitamin A dose on the market, available without prescription, is 25,000IU per softgel (meaning one daily dose), and we also consider that it is packed in polysorbate 80 and soybean oil for maximized absorption – it is likely that at least 12,500IU will be absorbed by our small intestine. Now, based on all I have read, it is impossible for the human body to use all 12,500IU in a day. They will get stored in the liver. Let’s say that at least 5,000IU of the 12,000IU get stored in the liver every day. That means that a liver will reach 150,000IU stored in 30 days of taking 25,000IU daily. I must say: these are reserved calculations. My personal gut guess will be for much higher accumulation, but I want to be conservative in what I am telling you. A human liver weighs between 1.44 and 1.66kg. Thus, we can calculate that 150,000IU distributed equally to 1,600 grams of liver will account for roughly 93IU/g. It very much seems that the human liver is not “designed” to carry huge amounts of vitamin A, not even when heavily supplemented. I’d humbly say: maybe we simply do not need that much?
However, back to the polar bear story, when you eat polar-bear liver, for each gram of liver you basically intake 18,000IU of vitamin A. For the sake of the argument, say that an arctic explorer’s portion was a measly 300 grams of liver. This will equate to a total one time ingestion of 300 x 18,000IU = 540,000IU. That is over half a million IU of vitamin A. No wonder the arctic expedition fellows got poisoned!
What should we learn from this? There is a lot of learning! First and foremost, be realistic about the fact that one bottle of 300 softgels of 25,000IU vitamin A each may easily take one to over 1 million IU vitamin A, if ingested all at once. I mean – people! – having this commercially available without prescription is very much like selling rat poison! It is simply unsafe, for God’s sake! This could fatally intoxicate more than one person. Agree, it would be a very displeasing taste to take them all at once. But taking one a day until you finish them all is not safer either!! Because vitamin A accumulates in the liver! IF really needed AND administered at the recommendation AND under the supervision of a clinical professional, that must be a dramatic case of vitamin A deficiency! Not everyone is THAT CASE. Do not get fooled! Never take them simply because your drug or grocery store has them on-sale and the word “vitamin” sounds healthy to you! Second, DO NOT take them because you want a nicer skin either! There are cosmetic creams with vitamin A for that purpose! They DO NOT get absorbed past your skin and DO NOT intoxicate you as rapidly! If nothing else, please remember this.
Let’s see what else happened with the experiments of Rodahl and Moore 75 years ago at Cambridge. They took portions of one gram of the polar-bear liver and fed them to rats. It seems that rats were reluctant to eat them (yeah, thought that was interesting!). The authors state:
“We have observed the same disinclination in rats when’ given the livers of other rats which had been allowed to accumulate very high reserves of vitamin A”.
Wow! Smart creatures…the authors go further describing one particular rat:
“One rat ate a total of 33.1 grams of the bear liver during a period of 22 days, an amount containing an average of 15,000 i.u. of vitamin A/day. It became anaemic and the hind legs were paralysed. When moribund it was killed. At autopsy, the profuse internal haemorrhage typical of hypervitaminosis A was found”.
We further find out that one rat who ate much less (5.3 grams of liver over 9 days) accidentally cut a paw on the wire of its cage. The poor fellow bled to death despite the small wound which wound have never caused a similar unfortunate end in a normal animal. It is terribly sad that these animals died, it is beyond upsetting that humans have died too. This all was for you to learn and tell others that generally healthy adults should NOT take vitamin A supplementation. In fact, the Food and Nutrition Board of the Institute of Medicine advises against beta-carotene supplements for the general population, except as a provitamin A source to prevent vitamin A deficiency (see Health Risks from Excessive Vitamin A). This recommendation does not apply to young children and pregnant mothers. The vitamin A requirements in kids and mothers, including lactating mothers are different. If you smoke, DO NOT take any form of vitamin A supplementation! Findings from the ATBC and CARET clinial trials show that beta-carotene and retinyl palmitate supplementation increased the risk of death, incidence of cardiovascular disease, and risk of lung cancer. Despite the Physicians Health Study showing no significant increased in cancer occurrence, we should be realistic that the premises of this more recent study evaluated a population with only 11% current and less than 40% past smokers.
I do not know about you, but I am not planning to supplement my vitamin A intake anytime soon. I am NOT juicing carrots daily either – although I love carrots! I do buy carrots for regular cooking, but none of us has ever turned orange! Sure, except for my mom, 20 years ago – a story that you can read here, together with my early vitamin A learning.
I am sure that you understand where I stand on this. Send me your feedback below or on the forum or contact me if you have any questions. I will be more than happy to discuss any specifics of a particular situation. Stay healthy in the mean time and say “NO” to the chef for the bear liver stew 🙂
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