Vitamin D: The History, Discovery and Role in Good Health

Interviewer: We're here with Dr. James Dowd, author of The Vitamin D cure. Tell us what vitamin D is, in a nutshell.

James E. Dowd MD, FACR, ABIHM: Well, vitamin D, we confuse it with vitamins because it has that label in front of it, but vitamin D belongs to the steroid hormone family. And we're familiar with that family. Cortisol is in that family; testosterone, estrogen, progesterone. And we know how powerful these hormones are, and vitamin D really shares a lot of the same functions with other members of its family and actually works with other members of its family to accomplish its tasks.

Interviewer: Why is it called a vitamin if it's a hormone? People know what hormones are and they know what vitamins are. Why did that kind of switch? 

James E. Dowd MD, FACR, ABIHM: Well, most of that has to do with history. When they were discovering these small molecules that they found were important and came from nutrient sources, they just started labeling them sequentially, A, B, C. And they came along to this molecule D, that was associated with bone and rickets and these sorts of problems that they were seeing, both in humans and animals at the time of the discovery. And so they thought it was food sourced and that this was the next small compound that fell in that same line of compounds.

Interviewer: What's its role in our body, vitamin D? Why do we need it? 

James E. Dowd MD, FACR, ABIHM: Well, vitamin D, as a steroid hormone, its primary function is to regulate calcium metabolism. Okay? So it's essential for absorption of calcium in our gut. So in the absence of vitamin D, we do not absorb calcium from our gut. So there's no passive absorption of calcium. You need the vitamin D. And it regulates calcium if your levels drop for whatever reason. It can take calcium out of your bone. It can reabsorb more from your urine and regulate this balance of calcium at any time in your life. Okay? So that's probably its principle function is calcium metabolism.

But what we've learned in the last decade or two, really, is that vitamin D is not only produced, but binds to and functions in almost every cell type in the body, and has very diverse functions beyond its calcium effects. And those are the ones that are really more interesting and that I wrote about in The Vitamin D Cure, that kind of takes you past the calcium equation into a lot more interesting stuff. 

Interviewer: Is that one of the reasons why we associate vitamin D with dairy products? I mean, you see it in milk and things like that, because the two go hand in hand? 

James E. Dowd MD, FACR, ABIHM: Yeah, so the dairy story is interesting. In the pre World War II era, when rickets, the bone disease in children, was really a pandemic. So whenever you went to urban centers, like New York City, London, Paris, Chicago, rickets was widespread. And so it was a serious problem in children who weren't out in the sun, who weren't playing and weren't physically active, and had very different diets in these poor urban areas than they did in rural areas. And so as a public health measure, the Federal Government says, "We got to do something about this because these kids are a mess. They have all kinds of problems, scoliosis, crooked bones, lousy teeth, and they have learning disabilities, they have heart failure. They have all kinds of other health problems related to this deficiency." And so they said, "We got to somehow get it in"--almost like get it in the water. But for kids, that happened to be, "Let's pick something that children are going to consume on a regular basis, that may also have some compatible, if you will, nutrients, and we'll add this to it and maybe this will fix the problem." And so that was their thought. 

Now at the same time in Europe, and in the United States, prior to fortifying milk, everybody was taking cod liver oil and that was an unpleasant experience. And so they said, "Well, maybe we can do something different that would raise compliance." And so they decided to add it to milk, so they fortified milk with A and D. That was around the same time the homogenization process started, so then you started seeing homogenized milk with A and D in it. And then that became sort of set into law. And the amounts that they put in milk of A and D are very effective at preventing rickets, but what we realize now is that those amounts are quite low and don't provide the amount needed for adults to normalize their D status. 

Interviewer: Okay. So we know that vitamin D is not actually a vitamin. It's a hormone. What's the difference between a vitamin and a hormone, in terms of their roles in the body?

James E. Dowd MD, FACR, ABIHM: Well, because the term vitamin was not. . . They didn't derive that term from some functional definition, that everything that functions in a certain way, we're going to call a vitamin and everything that functions in a different way, we're going to call it something else. Otherwise, a lot of the vitamins would disappear. Many vitamins are, sort of, co-factors in reactions. And so they catalyze certain reactions, enzymatic reactions, or they play an accessory role to increase the efficiency of, whether it be DNA replication or methylation of DNA or modification of proteins. 

And so they really, it's an antiquated term that was assigned historically, really in a timewise fashion to molecules as they were discovered. But it's not a unifying terms that tells us anything about what these molecules are doing necessarily. So many vitamins, like vitamin D is very different from vitamin C, is very different from folic acid and B vitamins that are important in methylation are very different from some other things.