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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

Why do we call vitamin D, vitamin D?

What is vitamin D? While the question would seem to call for a simple answer, the query hasn’t always prompted as straight forward a response as one might expect. Researchers often squabble over whether to classify vitamin D as a “vitamin,” a “hormone,” a “pro-hormone,” a “pre-hormone,” an essential “nutrient” and more. This might lead you to ask, then why do we call vitamin D, vitamin D?

The field of nutrition took off in the nineteenth century by German chemists. They believed that an adequate diet solely consisted of proteins, carbohydrates, fats and minerals; unaware of nutrients we now call vitamins.

Scientists began questioning this, as they noticed certain diseases, like scurvy and beriberi, could be prevented by certain foods. However, when these certain foods were “purified,” they somehow lost their ability to treat the diseases. A biochemist named Casimir Funk coined the term “vital animes,” theorizing that there were vital compounds called animes in food, essential to the diet of animals. This term paved the way for the now current descriptive word, “vitamins.”

Around 1916, Professor Elmer McCullum of the University of Wisconsin-Madison discovered that some type of fat-soluble substance in butter prevented xerophthalmia (dry eyes). He later called this factor “vitamin A.”

In later animal experiments, he used this butter and compared it to cod liver oil. He noticed that in animals that took cod liver oil, they developed neuritis, while the animals taking the butter did not. This was attributable to a set of vitamins they penned “vitamin B,” which was found in the butter but not in the cod liver oil.

Meanwhile, physicians elsewhere discovered a nutrient in food that staved off scurvy in guinea pig experiments. They followed suit and called this factor “vitamin C.”

Professor McCollum transferred to John Hopkins, continuing his experiments on fat-soluble nutrients. Cod liver oil was long known to prevent and cure rickets, and since McCollum and colleagues discovered vitamin A years earlier, they thought that vitamin A might also be responsible for curing rickets. McCollum wanted to know for sure, was it vitamin A or some other nutrient?

In another series of experiments, McCollum aerated and heated cod liver oil to destroy the vitamin A content. He knew he had rid the cod liver oil of the vitamin A because the altered cod liver oil no longer prevented xerophthalmia. When he used this cod liver oil in rickets experiments, it still retained its ability to cure rickets. Thus, he reasoned there must be another nutrient in cod liver oil that prevents and cures rickets.

And so McCollum named this new nutrient, “vitamin D.”

Around this same time, a different group of researchers carried out a set of experiments and independently found that sunlight or artificial UV light could prevent and cure rickets, too. While some scientists observed this connection as far back as a hundred years earlier, these experiments were the first to verify that sunlight indeed plays a role in rickets.

To the bewilderment of scientists at the time, somehow cod liver oil equaled sunshine, requiring much further investigation.

In the 1920s, Professor Harry Steenbock of the University of Wisconsin-Madison carried out a series of experiments, irradiating goats and their food and noticing again that UV light prevented rickets. Furthermore, he found that UV light activated an in-active substance into something vitamin D-like in foods. Thus, he established that UV light could both irradiate foods and animals and induce vitamin D activity.

In the 1930s, researchers were able to pinpoint the structure of vitamin D, and they were also able to identify the structure of its precursor in the skin, 7-dehydrocholesterol, which converts into vitamin D once exposed to UV light.

These findings raised the issue that maybe vitamin D is not a vitamin. A vitamin is called a vitamin when it cannot be synthesized in sufficient quantities by an organism. In these series of experiments, it was shown that with sunlight, rickets could be eradicated just as well with sun exposure as with cod liver oil. Thus suggesting, given adequate sun exposure, maybe the vitamin D from food isn’t necessary, and so maybe vitamin D isn’t even a “vitamin” in the true sense of the word.

This is something we speculate over now, but it is unlikely they speculated over what to call vitamin D then. The field of nutrition, still in its infancy, still didn’t know enough about vitamin D and still sought to know more about nutrition. The term “vitamin D” worked just fine.

About forty years later with advanced technology in place, researchers wanted to know what vitamin D converted into once it entered into the animal body. Through radiolabeling techniques, they discovered that vitamin D turns into 25(OH)D  and then into 1,25(OH)₂D. We commonly refer to 25(OH)D as your “vitamin D level” and “1,25(OH)₂D” as your “activated vitamin D,” the latter usually unimportant in a clinical setting.

This activated vitamin D, they realized, was a hormone, secreted by the kidney into the blood stream, part of a feedback loop with parathyroid hormone and calcium, telling the body how to maintain the right amount of calcium in the blood. This is the basis of why people sometimes refer to vitamin D as a hormone.

But this isn’t quite right either, as vitamin D is not a hormone itself, while its activated form is. Thus some choose to call vitamin D a “pro-hormone” or a “pre-hormone,” meaning that it helps, assists, is a precursor, and is necessary to the production of a hormone.

While this might be a bit more accurate of a description, I can’t envision a world in which we call vitamin D, “prohormone D” or some other name insinuating hormonal activity; mainly because it’s called “vitamin D” and always has been, regardless of the inaccuracy of the word “vitamin.”

And I’m not sure it matters so much. I’ve read my fair share of internet debates, some dim-witted:

“I’m not going to take a vitamin D supplement because it’s a hormone, and I don’t mess with hormones. I’ll let my body do the regulating.”

And some founded and hopeful:

“Doctors would take vitamin D more seriously if they knew it was hormonal.”

What’s important is that we improve the world’s vitamin D status. It’s not known if changing the name of vitamin D would improve this. My guess is that it wouldn’t.

In all this speculation, I think of biotin, a B-vitamin, and something no one takes because the body synthesizes it in the gut. Now let’s pretend for a moment that the research behind biotin is equally compelling to vitamin D’s: many people are deficient in it and treating this deficiency may prevent and treat many diseases. One solution to this issue would be to convince the public to begin supplementing with biotin.

As a guy who’s been out on the ground trying to explain that being aware of vitamin D is important, I can definitely say the word “vitamin” is on my side. It seems to lure people in, even if they know nothing of vitamin D, and how the body can synthesize it when out in the sun. They hear the word “vitamin,” and they assume that it must be something they need.

With biotin, I’m not sure I’m given this benefit. If biotin deficiency were a serious issue, I think there would be bigger barriers in its promotion, as fastidious as that might sound.

In conclusion, it’s interesting to know why vitamin D is called vitamin D, and why some argue that we shouldn’t call it a vitamin, rather a pro-hormone or something of the like. But from a public health standpoint, it’s probably unimportant getting this right and futile to get bogged down by specifics. In fact, the word vitamin might even play to its favor. For all we know, vitamin D could have been ill-graced with a name like biotin.

And without digressing further, what’s important is that we improve vitamin D status on the population level, and with that in mind, calling vitamin D — vitamin D — does just fine.

  About: Brant Cebulla

Brant Cebulla was a staff member for the Vitamin D Council from May 2011 to April 2014. He has keen interests in nutrition and exercise.

11 Responses to Why do we call vitamin D, vitamin D?

  1. pidkb@comcast.net says:

    Brant when you said “They hear the word “vitamin,” and they assume that it must be something they need”, I think reactions can go either way. If I am trying to tell someone about Vitamin D, I usually see the “scepticism” on their face first at the mention of a vitamin and the next words out of my mouth better be “It’s not really a vitamin but a prohormone” then I have their attention and they start to listen
    As someone already pointed out, a while ago, we have been inundated with things that in the end did not “pan” out as first reported. Eggs, that were, extremely bad for our health, Vitamin E that was going to work “miracles” etc. So who is going to really listen about one more vitamin or supplement “miracle”. We are usually told that if we “eat right” that we do not even need to supplement!
    I agree with Rita that calling it a “Vitamin” is so wrong and very misleading! (Too bad that naming mistake was made all those years ago!) I think we are stuck with it though!
    I have been seeing Alternative Health Care Providers for many years because I could find no help in “general medicine”. It was that first doctor that did a Vitamin D test and I was at 11ng/ml. He gave me the prescription Vitamin D to take. I tried to research the subject but at the time there was no “Dr. Cannell” only the Mayo Clinic. Over the years the doctors kept increasing the amount I should take. I finally decided to try and research again. Low and behold I found the Vitamin D Council. (God bless Dr. Cannell!)
    So what got my attention on the website. Vitamin D is a prohormone (the alarm bell started to sound) and that you can go outside in the middle of summer and make “thousands and thousands of units” all on your own. More warning bells! (And I thought thyroid hormone was the “be all end all” of hormones.)
    Never once in my lifetime or my children’s lifetime has one doctor even mentioned Vitamin D and that it actually comes from the sun striking our skin. Just what do they teach doctors at school especially Endocrinologists! This is the biggest medical snafu in history!
    Most people rely on their doctor for this kind of information. So I think that is where the effort needs to be. And “NO” it should not be “piggybacked” on another supplement or fortified in food.
    So how do you tell someone that Vitamin D is not a vitamin, that no they cannot get enough from their diet, that no they cannot make any in the wintertime, that no the 1000 units mixed with their calcium is not enough, no when the doctor tells you that your “level” is fine it probably is not try 50ng/ml and above, that all that talk about too much being dangerous is a myth, that people in charge of federal guidelines, are withholding information so they can make money “down the road”? What a tangled web!

  2. mbuck says:

    In casual conversation, vitamin D can be mis-heard as B, so I always add, ‘vitamin D–the sunshine vitamin’. I always make this association with sunshine because it’s the most natural way we get it. Because our skin can make so much in so little time, it functions like leaves converting light, water and soil into more trees.

    What happens to a plant removed from sunshine? It fails to thrive and withers.

    Thus enters a plethora of ailments, compounded with each succeeding generation.

  3. Ian says:

    In NZ, because it is referred to as a hormone it is virtually banned.
    It is not a hormone, it is a nutrient, mostly endogenously synthesised but also found in foods. The fact the kidney converts 25(OH)D into calitriol does not make vitamin D3 (cholecalciferol) a hormone.

  4. pidkb@comcast.net says:

    To Ian
    Then what is “Pregnenolone” is that also a “nutrient” by your standards? If you say Vitamin D is a nutrient people then think if they “eat right” they will have “no problem”.
    To Mbuck
    I am 54 years old and never heard the term “sunshine vitamin”! I think the term probably stopped before my generation. I will ask my older sibblings if they remember the term.

  5. Ian says:

    Pregnenolone has hormonal activity in vivo. Cholecalciferol does not, as far as we know. Cholecalciferol is also found in some foods, albeit in low concentrations. Nutrient does not mean “found only in foods”.

    Calling vitamin D a hormone only adds to the fears and rationale for restricting it as in Canada, Australia and New Zealand. Bad policy in my mind. Especially as these countries have vitamin D related diseases at high rates. I suspect there also movements in the US to exercise such restrictions too, fortunately Americans can still choose. It would be fine if medical practitioners were well informed and practiced unbiased medicine. You would be hard pressed to get a doctor in NZ to prescribe vitamin D, they too are full of unsubstantiated fears. None of them consult the Vitamin D Council.

  6. pidkb@comcast.net says:

    Ok Ian I see your point! Thanks so much for the insight. First I looked up “nutrients” figuring it would give me foods. It did but it also gave me “water”. Look closer and you find “oxygen” in the definition of “nutrient”. So knowing this I would get the vitamin companies to change the name to “Nutrient D”. Why? That alone might get people’s attention and spur more conversations and news coverage. I do not know if the FDA would approve of this or if they could even stop anyone from doing this. Anyway I think people could relate more in an explanation such as “Just like you need water, air, and food for vitamins and minerals you also need nutrient D. It separates it out from the “vitamins” and does not call it a “prehormone” to scare people and separates it from food because we all really know you can’t get enough that way. Of course education is paramount! When I say to people “it is NOT a vitamin” that gets their attention and then I try and explain. I think this will help me explain better or have an even bigger impact. Thanks! Thanks to Mbuck also I will watch out for the “mis-hearing” “D” as “B”!

  7. Ian says:

    Reinhold Vieth calls it a nutrient.

  8. The arguments about the naming of “vitamin D” have become completely irrational and an extreme waste of energy. To be absolutely correct vitamin D is not a vitamin since we can synthesize it ourselves, given the right conditions. The correct term therefore should be “conditionally essential nutrient”. What’s the condition? Lack of sunshine. If it is a hormone, then we should call the amino acid tyrosine a hormone, since it is the precursor for thyroxin, the thyroid hormone, and adrenaline and nor-adrenaline, the stress hormones. But no biochemist or physiologist would think of calling tyrosine a pre-hormone or a hormone. Its just plain silly.
    Incidentally, tyrosine is not an essential amino acid, since we can make it from phenylalanine, which is an essential amino acid. But under extreme stress the amount of tyrosine and phenylalanine available from diet becomes rate limiting for the production of stress hormones. So tyrosine is another example of a conditionally essential nutrient: It becomes essential when we are subjected to a lot of stress.

  9. Dan says:

    How about a new monker? VT = Vital Nutrient. But all cells having Vitamin D receptors makes it more a…

  10. “Vitamin D is to your body’s immune system and anti-inflammation, as estrogen/testosterone(depending on gender of listener) is to your sex. It is THAT powerful”.

    I find that most people react properly to this analogy. I often also remark, “a 5,000iu capsule has about 125 micrograms, a microgram is 1 THOUSANDTH of a milligram!, of D in it – that is how powerful the chemical is, and why your body makes it in as little as just 15 minutes at high noon in the summer if you run nekkid through the woods.”

    A little humor kind of embeds the notion….but I do it with a deadpan expression, till their eyes react. Then I smile, and say “there is probably nothing I do as a pharmacist to promote health more than to help you get to a mother-nature blood level of vitamin D. Just don’t get arrested doing it…”

    That’s one approach that seems to work well…

  11. Ian says:

    You expended quite a bit if energy there on such an irrational waste of time. I agree with your analogies. To add another, tryptophan is a precursor for serotonin and melatonin, both hormones.