Ironically, I have never heard of anyone overdosing on nutrients when the nutrients only came from eating real food. My guess would be if you eat liver every day for 2 weeks, you would naturally get sick of it and not want to eat it for a while. This would probably happen before you got vit A overload. Remember they are talking about daily intake, not just eating a bunch of liver on one day. Ever wonder why you 'get a taste' for some things on some days and other things on other days? It's one of the ways your body tells you what it wants you to eat.

When paleo is talking about eating 'lots' of organ meats, consider that most people don't eat any at all. One thing I do know is that all of the naturally living tribes always for for the organ meats first. There are probably a lot of reasons for this including they are nutrient dense and also perhaps they might spoil faster. But even wolves and carnivores eat the organs first so I am thinking it's mostly a health thing.

However, I do think you bring up a really good point in that one animal caught and killed is only going to have one set of organs and the bulk of the animal is going to be made of muscle meat. So in paleo times, there was probably a natural limit to how much organ meat could be obtained. I think again, the advice to eat a variety of healthy foods is the best advice. Organ meats are healthy but so are many other foods. Best to get a good mix. Unless you have severe food allergies, you need not put all your eggs in one basket.

I find the Vitamin A overdose stuff to be way overblown, especially with the Vitamin D Council joining the fray of late.

I eat beef liver once a week.

Liver has a lot of vitamin A, even beef and chicken liver. There's some evidence that more than 1000 IU per day of pre-formed vitamin A, or retinol, is associated with more cancer, among vitamin D sufficient people.

Vit D and Vit A are heterodimers, meaning they both activate the RXR nuclear receptor. A higher retinol intake means more all-trans-retinoic acid (the active form of vit A) --> which means more retinoic acid activtion of the RXR receptor --> which likely means less calcitriol (the active form of vit D) activation of the RXR receptor --> which may mean there is a less robust expression of vitamin D dependent genes.

Epidemiology out of Scandinavia supports this mechanistic line or reasoning, but nobody knows whether it represents a real phenomenon yet.

In the meantime, let evolution be your guide. If you think that hunter gatherers ate the equivalent of one beef liver per week (as somebody here suggested), go for it. Personally, knowing how much food there is in a cow (or auroch) I don't think the average tribe killed anything close to one cow per week per person. Also, hunter-gatherers did NOT eat dairy, a big source of pre-formed retinol. So, if you eat lots of butter, cream, and eggs, you're already eating a high retinol diet. If you add significant amount of liver, you're in the retinol stratosphere.

I certainly agree that one should exercise caution with supplemental vitamin A. I also agree that a varied diet is important. If the diet is sufficiently varied, then there's virtually no risk of getting too much vitamin A.

The conventional medical wisdom is that sustained doses over 20,000 IU per day are dangerous. That may or may not be true, but the published evidence to support this assertion is pretty weak. Of the published accounts I have read, including a very alarming report about a man who developed total liver failure, none of them validated the vitamin A intake.

I have personal experience with vitamin A, because I took it in very large doses for years in my youth and early 20s. A typical daily dose of fish oil based vitamin A was 100,000. I took it to treat asthma and chronic upper respiratory problems.

At 100,000 IU/d for weeks and months at a time, I had no symptoms of overt toxicity. Sometimes my skin would be slightly dry. I think it contributed to, rather than alleviated, my acne, largely through this skin-drying effect. I didn't get real symptoms of toxicity unless I took 130,000 IU/d and up, at which point I would get the characteristic signs, like bone pain, headache, etc. so I never did that for very long.

Taking these amounts made some of the doctors I saw extremely nervous. We did some liver function tests to be safe, but I always passed with flying colours. There was never a hint of trouble -- no hypercalcemia, nothing. When you consider the standard doses for Accutane (which is isotretinoin, a vitamin A analog) this shouldn't really be surprising.

While taking this amount of vitamin A, I never had any colds.

It was not all wine and roses. I did get small, strange blisters from time to time and seemed unusually prone to warts. I tended to feel cold. Large intakes of preformed vitamin A can have a thyroid-suppressing effect.

My point is this: first, because retinols occur in nature, it's at least likely that humans can tolerate a wide range of intakes, and second, there's probably enormous variability between people. My dad tried, but could never handle the doses I was taking.

Would I take these amounts today? No -- but I went with the best information I had at the time. There does not seem to be any evidence of damage, even temporary.

Given my experience, I suspect the anxiety over vitamin A is misplaced.

"The liver of certain animals — including the polar bear, seal, walrus, and husky — is unsafe to eat because it is extraordinarily high in vitamin A. This danger has long been known to the Inuit and has been recognized by Europeans since at least 1597 when Gerrit de Veer wrote in his diary that, while taking refuge in the winter in Nova Zemlya, he and his men became severely ill after eating polar bear liver. In 1913, Antarctic explorers Douglas Mawson and Xavier Mertz were both poisoned (and Mertz died) from eating the liver of their sled dogs during the Far Eastern Party."