I don't quite understand how come? I'm sure not everyone is eating liver?
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"Everyone" is a pretty broad group to be clinically "deficient". From the looks of it, a good amount of the SAD foods are fortified with it, and the grassfed eggs/dairy/meats easily provide a day's supply. So, unless you're avoiding organs / seafood / meat / dairy / SAD foods or fruits / vegetables / starches / herbs and unable to convert enough carotenoids over, you should be able to scoot by. Your average breakfast cereal has a ton of retinol, and I can hit 100% just in butter before I eat any food.
From what little I understand, vitamin A (in the form of retinal) is one of those things your body likes to have too much of IF you have plenty of the other stuff (vitamin D, for one). If you get it all from plant sources your body will hedge its bets (for fear of inadequate vitamin D etc...) and only convert enough beta carotene to retinal to stave off deficiency. If you get a lot of vitamin D (combine sun, food, and possible supplementation) then the more vitamin A the merrier (within reason) and, so, eat your liver and onions kids!
TLDR: I don't think you'll have a deficiency if you eat plenty of beta carotene but you won't reap the benefits of an excess either.
Not a scientist, no clue.
The paleo answer might be:
You're body only needs a small amount to stave off deficiency, but ideal intake and not being deficient are two different things. I may be making this up, but I think i've seen you only need 600iu of A per day...again probably made that up. Beta carotene I believe is converted at a 5-1 to 15-1 rate.
Again...no clue what I'm talking about.
Inefficient absorption doesn't mean you're vitamin A deficient. Inefficient conversion of beta carotene to vitamin A doesn't mean you're vitamin A deficient.
His 3% figure in human adults is an in vitro study, a test tube experiment, not a study in, you know, actual humans.
45% of humans don't convert beta carotene to vitamin A, he says. The study he's linked as been talked about before. They study just 11 men, hardly a number capable of estimating the general population! If you couple this would the equally small study in done with women before this… the numbers show that adequate vitamin A consumption inhibits beta carotene conversion, while low vitamin A consumption ramps up the conversion.
Downvote for Kresser. :(