Several commenters have asked for my opinion on recent statements by prominent health researchers that many Americans are suffering from unrecognized vitamin A toxicity. Dr. John Cannell of the Vitamin D Council is perhaps the most familiar of them. Dr. Cannell's mission is to convey the benefits of vitamin D to the public. The Vitamin D Council's website is a great resource.
Vitamin A is a very important nutrient. Like vitamin D, it has its own nuclear receptors which alter the transcription of a number of genes in a wide variety of tissues. Thus, it is a very fundamental nutrient to health. It's necessary for proper development, vision, mineral metabolism, bone health, immune function, the integrity of skin and mucous membranes, and many other things. Vitamin A is a fat-soluble vitamin, and as such, it is possible to overdose. So far, everyone is in agreement.
The question of optimal intake is where opinions begin to diverge. Hunter-gatherers and healthy non-industrial cultures, who almost invariably had excellent dental and skeletal development and health, often had a very high intake of vitamin A (according to Dr. Weston Price and others). This is not surprising, considering their fondness for organ meats. A meager 2 ounces of beef liver contains about 9,500 IU, or almost 200% of your U.S. and Canadian recommended daily allowance (RDA). Kidney and eye are rich in vitamin A, as are many of the marine oils consumed by the Inuit and other arctic groups.
If we can extrapolate from historical hunter-gatherers, our ancestors didn't waste organs. In fact, in times of plenty, some groups discarded the muscle tissue and ate the organs and fat. Carnivorous animals often eat the organs first, because they know exactly where the nutrients are. Zookeepers know that if you feed a lion nothing but muscle, it does not thrive.
This is the background against which we must consider the question of vitamin A toxicity. Claims of toxicity must be reconciled with the fact that healthy cultures often consumed large amounts of vitamin A without any ill effects. Well, you might be surprised to hear me say that I do believe some Americans and Europeans suffer from what you might call vitamin A toxicity. There is a fairly consistent association between vitamin A intake and bone mineral density, osteoporosis and fracture risk. It holds true across cultures and sources of vitamin A. Chris Masterjohn reviewed the epidemiology here. I recommend reading his very thorough article if you want more detail. The optimum intake in some studies is 2-3,000 IU, corresponding to about 50% of the RDA. People who eat more or less than this amount tend to suffer from poorer bone health. This is where Dr. Cannell and others are coming from when they say vitamin A toxicity is common.
The only problem is, this position ignores the interactions between fat-soluble vitamins. Vitamin D strongly protects agains vitamin A toxicity and vice versa. As a matter of fact, "vitamin A toxicity" is almost certainly a relative deficiency of vitamin D. Vitamin D deficiency is also tightly correlated with low bone mineral density, osteoporosis and fracture risk. A high vitamin A intake requires vitamin D to balance it. The epidemiological studies showing an association between high-normal vitamin A intake and reduced bone health all sported populations that were moderately to severely vitamin D deficient on average. At optimal vitamin D levels, 40-70 ng/mL 25(OH)D, it would take a whopping dose of vitamin A to induce toxicity. You might get there if you eat nothing but beef liver for a week or two.
The experiment hasn't been done under controlled conditions in humans, but if you believe the animal studies, the optimal intake for bone mineral density is a high intake of both vitamins A and D. And guess what? A high intake of vitamins A and D also increases the need for vitamin K2. That's because they work together. For example, vitamin D3 increases the secretion of matrix Gla protein and vitamin K2 activates it. Is it any surprise that the optimal proportions of A, D and K occur effortlessly in a lifestyle that includes outdoor activity and whole, natural animal foods? This is the blind spot of the researchers who have warned of vitamin A toxicity: uncontrolled reductionism. Vitamins do not act in a vacuum; they interact with one another. If your theory doesn't agree with empirical observations from healthy cultures, it's back to the drawing board.
High-vitamin cod liver oil is an excellent source of vitamins A and D because it contains a balanced amount of both. Unfortunately, many brands use processing methods that reduce the amount of one or more vitamins. See the Weston Price foundation's recommendations for the highest quality cod liver oils. They also happen to be the cheapest per dose. I order Green Pasture high-vitamin cod liver oil through Live Superfoods (it's cheaper than ordering directly).
This suggests that vitamin A toxicity may be less of a concern when vitamin D status is good.
33 comments:
Regarding bone density health: as a 53 year old male my doctor was very surprised (as I was) when earlier this year I was x-rayed and found to have osteopenia, the precursor to osteoporosis. he kept saying how unusual this was. I walk miles and miles each week but do not lift weights - the x-ray was due to a back injury from a very light schedule of weight-lifting and an accident involving slipping. More than likely I would not have been injured had my bone health been better.
I am wondering if "conventional" wisdom that men do not suffer bone density problems until later in life is masking another problem with our terrible nutrition in this country.
I need clarification regarding vitamins: you say sources for A + D can come from supplements? Any recommendations brand-wise, etc.
Also, what would you say as a biochem knowledgeable person: I keep wondering about synthetic vitamins and the right-handedness versus lefthandedness specificity of receptor sites - do you know what I mean? It's been 30 years since I had any biochemistry so I don't know if these terms are still used. In other words how many synthetic vites are just a waste of money if not actually dangerous? So what would you use for A + D sources?
Thanks for an interesting read based on interesting science!
Hi Sel,
This is not medical advice, just information. The most important thing is for you to increase your intake of vitamins K2 and D3. There have been a number of trials showing remarkable effects of K2 on bone health. Not surprising, since osteoporosis/osteopenia are probably caused by K2/D3 deficiency to begin with. It's important to get the MK-4 form of K2, also called menaquinone-4 and menatetrenone.
You can get D3 from sunlight (whether your skin makes D in the winter depends on your latitude), supplements or high-vitamin cod liver oil (I recommended a CLO in the post). If you supplement, go for 4-5,000 IU D3 if you don't go outside much. Don't take that much if you get a lot of sun. Vitamin D3 supplements come from wool oil or fish livers so are naturally sourced. The only way to know your blood level for sure is to have it tested. I wrote a post on vitamin D a while back if you want more info.
You can get vitamin K2 from pasture-raised butter (there's not much in conventional butter), the organs and fat of pastured animals, seafood and fish eggs. You can also supplement. I wouldn't take more than 1 mg per day. Thorne research sells drops you can use that are 1 mg apiece.
It may also help to balance your omega-6/omega-3 ratio. It impacts bone health. In practice, that means avoiding industrial vegetable oils like soybean and corn oil, and the processed foods that contain them. It also means eating more high-quality animal fats, especially marine fats like wild fish.
Vitamin A supplements typically supply all-trans retinol, which is the same form of vitamin A commonly found in animal foods. But supplementing vitamin A is unnecessary as long as you eat butter, eggs, liver and other organs.
I forgot to mention, the best K2 supplement is high-vitamin butter oil. Green Pastures makes it.
This is a somewhat related question to your post as I have been perusing your fat-soluble vitamin posts: something happened to me along with the bone density problem and that was kidney stones AND mild hypertension. I noticed one post regarding vitamin D a discussion of the kidney: “The kidney converts 25(OH)D3 to 1,25(OH)D3 as needed. This is the major hormone form of vitamin D. 1,25(OH)D3 has profound effects on a number of tissues.” And “Low vitamin D levels associate with nearly every common non-communicable disorder, including obesity, diabetes, cardiovascular disease, autoimmune disease, osteoporosis and cancer. Clinical trials using vitamin D supplements have shown beneficial and sometimes striking effects on cancer, hypertension, type 1 diabetes, bone fracture and athletic performance. Vitamin D is a fundamental building block of health.”
Finally, another post said “The body clearly has mechanisms for creating and preserving bone density in the face of an acid-yielding diet, it's just a question of whether those mechanisms are working properly.”
I’m obviously groping here but I wonder how the body’s mechanism (especially my body’s mechanism) reacts to poor diets. I look at the irony of me growing kidneys stones, which when tested, were the common calcium oxalate, while my bones were becoming thinner……One thing the nephrologist told me is that my urine lab work showed uric acid crystals, precursors to stones.
Any ideas or directions, links to send me to, or have you any posts, as it seems to me there might be correlations between kidney stones and osteopenia.
Sel,
You might want to look at your Omega 3:6 intake.
Balance your Omega3 and 6 plant based fats. Intake of Omega 6 should be low under 2% or 3% calories depending on whose figures you accept.
Most common vegetables oils are very high in Omega 6, and they are the main source of the problem.
Get at least a grams day of DHA and EPA combined in the form of oily fish fish oil etc.
High Omega 6 and low Onega 3 links to lower bone density in men and women.
Improving the Omega 3:6 status also reduces oxidative stress, and inflammation.
Stephan has some good posts and I have written a book on the subject which I am currently updating.
There is a resource page on my web site.
Robert Brown
Author
Omega Six The Devils Fat
www.omegasixthedevilsfat.com
Hi Sel,
Kidney stones may be a symptom of vitamin K deficiency. They are becoming more and more common, even in kids. Vitamin K2-dependent proteins prevent the precipitation of minerals in the urine. See this link for a discussion of it:
http://www.gofrolic.org/gofrolic/food_blog/Entries/2008/10/28_Kidney_Stones_Increase_in_Kids%3A_A_matter_of_diet.html
Elevated uric acid suggests that you eat sugar regularly; is that the case? It's typically a result of too much fructose (from sugar). Some doctors will tell you to cut back on meat if your uric acid is too high, but meat is not the problem.
I think cutting back on fructose and increasing your intake of fat-soluble vitamins (particularly K2) would be an effective preventive strategy for kidney stones and health in general.
A working link for the kidney stone post is here.
Your argument makes sense, especially since we've lost so many of our natural sources of vitamins D and K, but still get a decent amount of vitamin A from food. Vitamin A toxicity would be yet another symptom of D and K deficiency.
Debs
Food Is Love/Seattle Local Food
Thanks to all of you: Stephan asked if I eat sugar and after his most recent post on the glycemic index with the high serum uric acid levels due to fructose consumption made me see myself as self-deluded.
Obviously I am new to this blog but I have already begun to make more sense out of my own health than with all the various one-point-of-view books I've read on nutrition and even the Mayo website. And I go to Mayo here in Jacksonville for my health needs!
After I read the most recent post I called my nephrologists office and found out that yes, my uric acid level was too high and that crystals were seen in the urine.
My nephrologist and my urologist both suggested that I cut back on fats/meats; never once has anyone, except my family practitioner, suggested I look at the fructose content of my diet.
My wife is a part-time cake and sweets baker; weddings, birthdays etc. Guess who is asked to taste all her work? Guess who has all the extras/overmades after dinner every night, (just about)?
Guess who is walking away from all that?
And looking hard at my total caloric intake I failed to realize that even with a correct daily caloric total if the fructose amounts are 25% (? I'm guessing) of an otherwise healthy total you are missing out on the minerals, vitamins and the needed fat to help metabolize it correctly.
I have walked and walked for the last year, sometimes walking up to seven miles at a time, almost always 3 miles and yet my weight never went down past a point. It seems ridiculous now but I really thought that being below a certain caloric total + the exercise = weight loss AND better health.
It has not been so, much to my frustration and some despair.
Sadly, nutrition is not much of a component of a doctor's training.
I am ever gathering data and will start both a food journal and an exercise journal soon and keep reading everything I can find.
I can't say how much I appreciate the complexity of the whole subject and cringe at my lack of judgment in embracing simplistic "popular" dieting fads.
Moderation is all things someone said....
Many thanks to all of you. Thanks to all of you: Stephan asked if I eat sugar and after his most recent post on the glycemic index with the serum uric acid levels due to fructose consumption made me see myself as self-deluded.
Obviously I am new to this blog but I have already begun to make more sense out of my own health than with all the various one-point-of-view books I've read on nutrition and even the Mayo website. And I go to Mayo here in Jacksonville for my health needs!
After I read the most recent post I called my nephrologists office and found out that yes, my uric acid level was too high and that crystals were seen in the urine.
My nephrologist and my urologist both suggested that I cut back on fats/meats; never once has anyone, except my family practitioner, suggested I look at the fructose content of my diet.
My wife is a part-time cake and sweets baker; weddings, birthdays etc. Guess who is asked to taste all her work? Guess who has all the extras/overmades after dinner every night, (just about)?
Guess who is walking away from all that?
And looking hard at my total caloric intake I failed to realize that even with a correct daily caloric total if the fructose amounts are 25% (? I'm guessing) of an otherwise healthy total you are missing out on the minerals, vitamins and the needed fat to help metabolize it correctly.
I have walked and walked for the last year, sometimes walking up to seven miles at a time, almost always 3 miles and yet my weight never went down past a point. It seems ridiculous now but I really thought that being below a certain caloric total + the exercise = weight loss AND better health.
It has not been so much to my frustration and some despair.
Sadly, nutrition is not much of a component of a doctor's training.
I am ever gathering data and will start both a food journal and an exercise journal soon and keep reading.
I can't say how much I appreciate the complexity of the whole subject and cringe at my lack of judgment in embracing simplistic "popular" dieting fads.
Moderation is all things someone said....
Many thanks to all of you.
Hi Sel,
Glad to hear it makes sense. Keep us filled in on your progress!
I just learned of a Norwegian study of 3000 women between the ages of 50 and 70 which found that those who had taken cod liver oil as children had less bone density than those who did not. It surprised the researchers. I'm wondering if high-vitamin cod liver oil might be too much of a good thing?
Deb,
Just took a look. It's a bizarre paper. First of all, they're looking at the childhood CLO intake of women who are 50-70 years old, and drawing associations. That's a long time between cause and effect! I'd be interested to know if there were other differences between the groups in childhood, for example, if people in certain socioeconomic groups were more or less likely to give CLO. They are also relying on these womens' memories of how frequently they took CLO as children. The finding is difficult to interpret in my opinion.
The second strange thing is they found no association between current CLO consumption and BMD, yet they chose to focus on the childhood association in the abstract. They didn't even mention the fact that current CLO consumption is not associated with reduced BMD, which is quite a big omission.
I don't find this study to be a challenge to cod liver oil at all. But I still think it's a good idea to make sure your vitamin D intake is adequate anytime you are eating a lot of vitamin A. High-vitamin CLO has a favorable ratio of A to D (10 to 1 by weight), while some supermarket varieties have a poor ratio (20 to 1 or higher) that could perhaps contribute to reduced BMD.
I heard about the Norwegian CLO study on NPR a while back. If I remember correctly (it's too close to bedtime to dig it up just now), they said that they believed that it could be excess vitamin A added to the oil that ultimately caused an imbalance in D. Does that make sense? I'm sure you can find the story at NPR's website.
P.S. This is a lovely blog. It has just the right combination of average joe and science.
Thanks Julie; that would be a logical explanation. It may have been in the paper, I didn't read it very carefully.
Maybe they didn't focus on the current use of CLO because, as I understand it, Norway etc. has changed the amount of Vitamin A they allow in the CLO, afraid of Vit A overdose. I'm just guessing, but I think high-vitamin CLO is more like the type of CLO these women would have had as children.
Stephan,
Great summary here! How about the converse: when taking higher doses of vitamin D, how important is increasing vitamin A intake to avoid toxicity of D?
Secondly, did you see the latest Vitamin D Council newsletter that Dr. Cannell sent today? (It's not on the website yet.) The topic is vitamin A toxicity. Cannell says that no extra vitamin A is needed while taking vitamin D. He also seems to think that carotenoids can supply the vitamin A requirements in a typical diet, which I think is questionable given their poor conversion to retinol.
Cannell also makes the following statement, which IMO is ridiculous: "The idea that the human genome evolved eating liver is absurd. By the time humans could hunt large mammals, the genome had already evolved. Humans evolved eating a diet not dissimilar to the Great Apes, vegetables, fruit, roots, and some bugs."
Hi Tom,
I did see Dr. Cannell's latest newsletter. Apparently Dr. Cannell doesn't have a foundation in human archaeology or anthropology as it relates to diet. We've been eating meat in significant quantities for a good 3 million years, and our closest recent relatives, the Neanderthals, were carnivores.
It's frustrating to see him making categorical statements like that when he clearly hasn't looked into it in detail. All it would take is a 5-minute call to an archaeologist or nutritional anthropologist to set him straight.
I do think it's important to maintain vitamin A levels when vitamin D levels are high. It's probably not as important as the converse, though.
I received the newsletter focusing on vitamin A toxicity and the "dangers" of cod liver oil also. Couldn't help but wonder if the scare tactics about getting nutrients from cod liver oil will boost the sales of the vitamin D supplements Cannell is telemarketing. How to boost sales: While making folks scared to use cod liver oil, provide them with the solution--the vitamin pills you just "happen" to be selling. He announced the launch of the vitamins in the Oct. 2008 council newsletter. Strange coincidence?
http://www.vitamindcouncil.org/newsletter/2008-october.shtml
The product description is here:
http://www.purityproducts.com/product.asp?sku=1203&dept%5Fid=41&mscssid=DPR94UWKJGPS8P45KVGTG86XVBRS4S9F#details
p.s. This is my first post here & don't know if the links will fit in ok.
I received the newsletter focusing on vitamin A toxicity and the "dangers" of cod liver oil also. Couldn't help but wonder if the scare tactics about getting nutrients from cod liver oil will boost the sales of the vitamin D supplements Cannell is telemarketing. How to boost sales: While making folks scared to use cod liver oil, provide them with the solution--the vitamin pills you just "happen" to be selling. He announced the launch of the vitamins in the Oct. 2008 council newsletter. Strange coincidence?
http://www.vitamindcouncil.org/newsletter/2008-october.shtml
The product description is here:
http://www.purityproducts.com/product.asp?sku=1203&dept%5Fid=41&mscssid=DPR94UWKJGPS8P45KVGTG86XVBRS4S9F#details
p.s. This is my first post here & don't know if the links will fit in ok.
Hi Zoey,
Interesting. I'm going to give him the benefit of the doubt this time but I'll keep my eyes peeled.
A large carrot contains roughly 10,000 IU of vitamin A; so eating a lot of carrots (like I do) could give you an A - D imbalance? Does the body metabolize Vit A differently from carrots? I'm 51, have never had a fracture or break in my life, and a recent x-ray (for a sports injury) showed that I have really good bones (at least in that leg!). Very informative blog.
Hi Bruce,
Here's the thing. Carrots contain beta-carotene rather than true vitamin A. The digestive tract converts a fraction of beta carotene to vitamin A, somewhere around 1/10 or 1/12 of it. Sometimes less. It depends also whether there is fat in the meal, with more fat leading to greater conversion.
So carrots really don't supply as much vitamin A as is claimed, not even close. In fact, excessive beta-carotene may actually interfere with vitamin A signaling. Nutrition information will list beta-carotene as if all of it will be converted to vitamin A, which is really misleading. You can divide those numbers by 10, at a minimum. Animal sources of vitamin A are true vitamin A so there is no need for conversion.
hi Stephen,
Thank you. It seems like nutrient metabolism is just as important a factor as food choices themselves. I'll share this info with my family members.
I wonder if Dr. Cannell is pro-vegetarian? That would explain his strange view of our nutritional history and his endorsing vegetable sources of vitamin A (or betacarotene).
He is an old peace/social rights activist, so that would fit in the stereotype too... ;-)
http://www.vitamindcouncil.org/cannellBiography.shtml
Do you like the regular cod liver or the fermented version more, and why??
Michael,
I've been taking the fermented version because it's less processed. It's a matter of principle.
Hi Stephan,
I was wondering about the effects of relatively rapid weight loss on your levels of fat soluble vitamins. When switching to a more paleo lifestyle (many thanks to you and your fellow blogites), I lost 20lbs in a matter of weeks. I know a fair amount of this would be both glycogen and water, but what happens to the vitamins stored in your own body fat when you burn thru it? Is there a possibility of reaching excess levels?
I'm asking because 7 months later, I've been diagnosed with kidney stones, even though I'm doing everything I thought was right, (vitD,K2/O3 supplements, paleo diet/exercise etc).
Do you think a sudden change in diet could precipitate kidney stones, or are they more likely a remnant of my previous lifestyle, come back to haunt me?
I do recall noticing that during my weight loss phase, my skin seemed very dehydrated all the time, no matter how much water I drank...
Hi Pete,
I really don't know. Sorry to hear about your kidney stones. That is rather suspicious timing, isn't it?
Nephropal has written quite a bit about kidney stones
He's a NEPHROLOGIST with a Paleolithic Standpoint so what he says is interesting.
If you use Control F enter stone in the new searchbox you will be able to find all the references.
I didn't know "Magnesium is an inhibitor of kidney stones."
If you have recently improved your vitamin D status that may affect our calcium levels as your body can now absorb more from calcium from your diet.
The actions of calcium are counterbalanced by magnesium.
So raising Vit d raises calcium and reveals mangesium deficiency.
Dietary Magnesium deficiency is almost as common as vitamin d deficiency.
Like those with kidney stones I'm supposed to pass 2 litres of urine a day. I find drinking sufficient water to produce that amount challenging. (My problem isn't kidney stones though)
Stephan,
There's another vit D council newsletter on the topic. Cannell postulates that because (i) there is little seasonal variation in serum vit D levels in Scandinavia (I guess implying more vit D intake is dietary) and (ii) cod liver oil is commonly consumed in there, the people with the highest vitamin D levels in these countries may also have high very retinol intakes, on average.
Cannell postulates that retinol thwarts some of the anticancer effects of vit D, perhaps because retinoids activate the RXR/VDR less robustly than does calcitriol.
Cannell further postulates that the correlation between high intakes of vitamin D and very high intakes of retinol in Scandinavia account for the relatively narrow U shaped curve for vit D in several population studies there (on colon, prostate, and pancreatic cancers).
I also noticed that the most positive vit A study of which I am aware was based in Sweden. (See http://www.ajcn.org/cgi/content/abstract/85/2/497.) This study found that those in the 4th quartile of vitamin A (median 5933 IU/day) fared better than those in the 3rd quartile (median 3810 IU/day).
It's unclear if the implications work in reverse in Sweden: high retinol intake implies high cod liver oil intake implies high vit D intake. If so, the protective effect found for vit A in this gastric cancer study may in fact be due to vit D and not vitamin A.
Also, I'm not sure how much retinol early humans would have had. There is only 1 liver per animal, and they didn't consume dairy. Even eggs may have been seasonal. The Inuit are an exception and do not define our evolutionary history. Vit D on the other hand was strong all year long in the Tropics.
Stephen,
Came across the Feb 2010 Newsletter from Vitamin D council.
http://www.vitamindcouncil.org/newsletter/vitamin-d-vitamin-a-and-cancer.shtml
I have been supplementing Vitamin D3 and A (thru green pastures CLO). I have stopped CLO for now. I do not know what to do.
Can you please comment?
Thanks Venkat
Light-mediated retinoic acid production
If it is the case in human that light exposure increases Vitamin A synthesis then it may be the case, in Northern latitudes where UVB exposure is limited but light intensity may be higher when reflected from snow, the potential for Vitamin A toxicity is higher.
Hi Stephan
I think cod liver oil is getting cornered. I have been taking cod liver for some time to compensate for the lack of sunshine, as I do continuous night shift and hardly see the sun all week long, as I get up around 15h and spend the rest of the afternoon inside. Cod liver is very similar in composition to CLO, as it is almost entirely made up of fat, with the difference that it is delicious, too, and can be eaten on a toast with pepper and chopped onions. Recently, having been alarmed by some articles on vitamin A toxicity that I found accidentally on the Net, I decided to do some research on my own. There is a lot of controversy about the issue, nevertheless a serious scientific report has convinced me to stop eating cod liver. Here is the link:
http://www.csuchico.edu/grassfedbeef/research/documents/sources/Melhus%20H%20%20PDF.pdf
I think, it is a fairly reasonable approach, if you want to test a particular foodstuff, to look for a part of the world, where it is widely consumed. If you are curious about the effects of beer drinking, go to Germany, for rice, go to China etc. The largest amount of cod liver (the stuff itself or its oil) per capita, I reckon (it has to be verified, though), is consumed in Scandinavia. According to the study I refer to, the bone health of the Scandinavians is nothing to boast about, it is one of the poorest in Europe.
The study is not perfect, it’s true. It relies on self-reporting, to begin with. Anyway, the diagnostics as to bone health are scientific. Its principal short-coming, I reckon, is that it does not differentiate between the sources of vi-tamin A, whether it is fortified milk, or CLO. They chuck it all into the same hat. We don’t know for example, how the Swedish fortify their skimmed milk, do they add natural substances to it, or synthetical vitamins.
Some more sophisticated research will be needed to sort out these details. Anyway, while I am waiting for them to be undertaken, I thought it wise to suspend cod liver consumption, at least on a daily basis. I experience it as real loss, it was so delicious. I am completely at a loss as to what vitamin D sup-plement to take now. Maybe I will have to opt for a syntetical pill, at least I am not aware of any other natural stuff that could be used as vitamin D supple-ment other than cod liver. If someone has a suggestion, give me a hint, please.
One more remark: It is not true that our ancestors all thrived on organ meat. I have come across an article stating that some bones dating back to prehistoric times (homo erectus) show the typical signs of hypervitaminosis A, presumably as a result of over reliance on organ meats.
Stephan, if you have a comment, I am curious to read it.
I would also like to see Stephan's take on the studies in the above posts. The Vitamin D Council one, which I read, seems somewhat rhetorical, calling cod liver oil a "poison" and assuming Scandinavians must get all their D from cod liver oil because they are Scandinavians, therefore their health problems are to blame on Vitamin A from cod liver oil, seems rather tenuous reasoning.
I am more concerned with this scientific paper I came across:
Alcohol, vitamin A, and ß-carotene: adverse interactions, including hepatotoxicity and carcinogenicity which seems to indicate any sort of A supplementation, either beta carotene or retinol, is bad news if you drink alcohol. Since I enjoy wine and beer, does that mean I should not supplement A at all? I thought A supplementation was essential if one is taking D and K2, at least for those of us not getting enormous amounts of beta carotene from vegetables.
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