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You might be familiar with vitamin A. Necessary for good eyesight, among other things, Vitamin A is one of the essential fat-soluble vitamins required in the human diet.
You may have also heard of where to get it. "Carrots, along with other orange and red vegetables are a source of vitamin A," says Livestrong.com, along with most popular sources on the topic.
Easy enough right? Just get your daily serving of carrots, and you'll avoid all the symptoms of vitamin A deficiency. The only problem is, there is no vitamin A in carrots.
But I must be mistaken–after all, the FDA says carrots have 110% of the RDA of vitamin A, and surely they wouldn't lie?
Unfortunately, it is my obligation to inform you that this is nothing other than a blatant lie. Carrots don't have vitamin A any more than dry ice is made of water.
Perhaps I'm being uncharitable. Carrots do contain a compound that is kind of like vitamin A. But it's not equivalent to vitamin A. In other words,
This compound is of course none other than beta-carotene, a chemical most are familiar with because it's considered to be vitamin A.
Perhaps it's time to more accurately define what vitamin A is. Vitamin A refers to a group of mostly interchangeable compounds including retinol and retinal. These compounds, also called "pre-formed vitamin A", are used directly by the body. Given their structural similarities, people generally refer to them all as "vitamin A".
It's worth mentioning that the pre-formed vitamin A compounds, retinal and retinol, are exclusively found in the diet from foods of animal origin. Conversely, plant foods only contain beta-carotene.
The important point here is that carrots contain beta-carotene, which is not the same thing as retinol/retinal, aka Vitamin A.
So why does the FDA use them interchangeably when talking about the nutrient content of vegetables?
Beta-carotene is sometimes called pro-vitamin A. The reason being, that it can, under the right circumstances, be converted by humans into actual pre-formed vitamin A.
This conversion process is highly variable, somewhat poorly understood, and dependent on a number of circumstantial factors, including the amount of fat you ingest along with it, your DNA, and your current levels of vitamin A.
Estimates for conversion efficiency are around 9-22%, and the efficiency of the conversion decreases the more vitamin A you have (p. 86 of Dietary Reference Intakes).
However, another study points to a "huge interindividual variation of beta-carotene conversion efficiency, possibly due to genetic polymorphisms."
And despite all the research, the question remains controversial. One paper on the subject writes
the notion that the efficiency of conversion of provitamin A from actual food sources such as carrots and dark green leafy vegetables was as high as the convention dictated was questioned. Such an overestimation was deceptive both in the degree that a true problem might be overlooked or underestimated and in the risk that a food-based prescription would be overly optimistic and inappropriate.
It's clear that the actual amount of vitamin A derived from plant foods is largely miscalculated. In particular,
we are currently over-estimating the usual intakes of vitamin A, especially those high reliance on plant protein
However, it's based on this conversion math that researchers have defined the term "Retinal Activity Equivalence (RAE)", which is used to translate between beta-carotene and pre-formed vitamin A based on this expected conversion percentage.
This is the mechanism by which the FDA allows beta-carotene content to be labeled as "vitamin A". When you look at the RDA of vitamin A for carrots, for example, it's actually beta-carotene measured in RAE (the amount of pre-formed vitamin A you're "expected" to get after your body converts it). Of course, those details are omitted from the label.
This sounds good in theory, but it assumes the conversion process is consistent and reliable. Since the conversion efficiency is so variable, in practice this equivalence isn't correct.
It's like if you went to buy a car, and you picked out the model, wired the money, and when it's time to get the keys, the dealer gives you four wheels, an engine, a chassis, and a box of spare parts. Technically, everything needed to make the car is there, but most of you won't actually be able to assemble those parts into a complete car. And you'd probably be pretty pissed.
Selling beta-carotene as vitamin A is similar. You've been told you're getting vitamin A, but you really ended up with a box of parts that could be vitamin A, but most likely won't end up completely assembled.
That's why technically, the FDA isn't completely lying when it talks about beta-carotene as if it were vitamin A. But based on the nuances of this conversion process, I'd argue it's pretty misleading.
Why should we care
The main takeaway from the above is that we are not getting enough vitamin A, even if we think we are. Despite following the FDA's RDA, if the "vitamin A" you're eating is beta-carotene, you are most likely not getting enough due to overestimated conversion.
This is a significant problem, since vitamin A is extremely important. Bad skin, bad eyesight, improper fetal development, immune failure, reproductive problems, etc. can all be caused by vitamin A deficiency. And the RDA is only designed to prevent deficiency– the proper amount for optimal health is unclear, and is most likely much higher (this will be a follow up discussion, but the vitamin A intake of healthy hunter-gatherers was orders of magnitude higher than ours).
This false equivalence should be quite perturbing, because it would lead to nutrient deficiency even if you're doing everything "correctly".
What can we do?
If vitamin A is so important, and its intake so underestimated, we must increase our dietary intake.
How do you know if you're deficient? Since the most dense sources of it are rarely consumed in a typical modern diet, and the common sources are not very potent, unless you make a conscious effort to consume a lot of pre-formed vitamin A, then you're probably deficient.
The solution to this is simple of course– eat foods with high amounts of pre-formed vitamin A. The most vitamin A-dense food by an order of magnitude is liver of any variety. Beef, pork, chicken, or fish liver, notably cod liver oil, are all ridiculously potent sources. You can generally find these in pill form if you'd prefer not to deal with sourcing and eating high quality organs.
Some types of seafood are also potent vitamin A sources, notably eel and tuna.
Another option that may be a bit more palatable is to eat butter– yes, butter.
Since when does butter have vitamins in it? Since always in fact, it's just not commonly talked about.
Note that ghee (mentioned above) has an order of magnitude more vitamin A than sweet potatoes, and ghee is of course none other than clarified butter (aka butter with residual milk proteins removed).
The vitamin A content of butter used to be well known, and has been widely studied, albeit not widely promoted. We can see from a number of sources that butter can range from 200-1000 micrograms of vitamin A, depending most significantly on the cows' diet and the time of year.
As an aside, all of these molecules are yellowy/orange, and this accounts for the orange color of veggies high in beta-carotene, as well as the yellow tint of high quality animal foods, such as butter, cheese, and the fat of grass-fed beef.
This was a lot to digest, so let's go over the key points
- In the context of plant foods, "vitamin A" actually refers to beta-carotene
- Beta-carotene can be converted by humans into pre-formed vitamin A (retinol and retinal), which is actually used by our body
- The conversion process is highly variable, inefficient, and self-limiting, and foods that contain beta-carotene don't have that much compared to foods with pre-formed vitamin A.
- Therefore foods containing beta-carotene should not be relied upon as a potent source of vitamin A
- Vitamin A is extremely important, so we must seek out the pre-formed compounds in our diet
- Foods such as liver, cod liver oil, seafood, butter, and ghee are good sources of pre-formed vitamin A
By now, I hope you've seen the importance of vitamin A, and that even in modern times with all our food security, it's quite easy to get too little of this important micronutrient. I'd also like to stress it's not very difficult to get more of it, if you incorporate some of the foods I mentioned.
I'll conclude this post with a quote from the study above that I think sums up the main problem of modern health nicely:
Agriculture is a system that provides better caloric security than its hunter-gatherer predecessor. The transition has sacrificed food diversity and micronutrient adequacy.
If you found this information valuable, someone you know might be interested as well. Feel free to forward this email, and help your friends learn what nature knows too.