The following is part one of an eight-part interview with Dr. Michael Holick, author of "The UV advantage" and one of the world's most respected authorities on vitamin D and the health benefits of natural sunlight. His work can be found at www.UVadvantage.com . Be sure to print out the vitamin D myths, facts and statistics page summarizing the key points of this interview.

Adams: Today we're speaking with Dr Michael Holick, Thank you for joining us today Dr Holick.

Dr. Holick: Oh, it's my pleasure.

Adams: For those who may not be familiar with your work and your website, can you give a brief introduction of what you cover and how you got into it?

Dr. Holick: Sure, I've been doing research in the vitamin D field for, now, more than 30 years, and I happened to be in the right place at the right time as a graduate student at the University of Wisconsin, and worked with one of the authorities in vitamin D, Dr. Hector DeLuca. As a graduate student my PhD project was actually the isolation and identification of the active form of vitamin D, and my roommate and I, over the next two years, were the first to chemically synthesize it. And what was really neat about that experience was that we actually gave this to patients when I was in medical school -- and patients that had bone diseases associated with kidney failure, that were wheelchair bound, that had severe bone pain started walking again.

That was my first introduction into one of the major benefits of activated vitamin D and the development of it for the treatment of a bone disease.

Adams: Does this mean you and your colleague were the first to synthesize this form of vitamin D?

Dr. Holick: Yes, the active form of vitamin D that's made by the kidney, it's called 125-dihydroxy vitamin D.

Adams: Is this procedure more widely used now, for example to make vitamin D supplements?

Dr. Holick: No, because this active form of vitamin D is available only by prescription. It's used to treat osteoporosis in Europe and Japan. And it's also used to treat bone disease and kidney failure patients, and has a lot of other uses as well.

Adams: So as you were doing the research on this, you were able to immediately observe the health impact of it, right away.

Dr. Holick: Exactly, and what we began to realize was that vitamin D was much more complex than thought. We always knew that vitamin D was made in your skin when you are exposed to sunlight, but it was only in the 1970s that it was finally appreciated that it actually had to go on this circuitous journey, first to your liver to get hydroxylated, kind of activated, modified -- what's called 25-hydroxy vitamin D - it's the major circulating form of vitamin D that doctors should be measuring in your blood to determine your vitamin D status. But that is also inactive, and it has to go to your kidneys, and then in the kidneys it gets modified again, to its active form, which we call 125-dihydroxy vitamin D. And it's this 125-dihydroxy vitamin D that's responsible for telling your intestines to absorb calcium from your diet more efficiently, and to make sure that your blood calcium is normal and that you have healthy bones.

Adams: So if there is a failure of any of these body systems along the chain, that can suppress the circulating active vitamin D then?

Dr. Holick: Exactly, and in fact if you have severe liver disease, for example, you have two problems. One is that you may not be able to modify it, to get the 25-hydroxy vitamin D, and secondly if you have a fat malabsorption problem where you can't absorb dietary fat, since vitamin D is a fat-soluble vitamin, then you can't absorb vitamin D and you become deficient in vitamin D. Then if you have any kind of kidney disease, you need either activated vitamin D or one its analogs in order to be able to maintain healthy bones.

Adams: In the testing then that you mentioned, was this active form being given through injection?

Dr. Holick: You could either take it orally or by injections.

Adams: Interesting. So you mentioned the positive impact on people who had trouble walking, who had osteoporosis, and various bone diseases. What other effects did you observe?

Dr. Holick: We also realized a few years later was that your skin doesn't only make vitamin D, which I think we'll talk about a little bit more in a minute, but it also recognizes activated vitamin D. And what was really, to me, quite amazing, was that in 1985 we realized the possibility that if you take activated vitamin D and put it in skin cells that you culture from humans, it turns out that activated vitamin D was probably one of the most potent inhibitors of skin cell growth. So I reasoned back in 1985 that if that was true, maybe you could take advantage of it by developing it to treat the hyperproliferative skin disorder psoriasis. And indeed it's one of the treatments of choice now worldwide. Both activated vitamin D and its analogs are used worldwide as the first line therapy for treating psoriasis.

And so again it shows you the breadth of activity that vitamin D has. Not only just to regulate calcium metabolism and bone health, but to regulate cell growth. And that's why we started realizing that people who live in higher latitudes and are more prone to vitamin D deficiency and are more prone to developing common cancers and dying of them, such as cancer of the colon, prostate, breast and even ovaries. And we think that that's in part due to the body's inability to make enough activated vitamin D to help regulate cell growth and to keep cell growth in check.

Adams: That would explain the links between breast cancer, prostate cancer, colon cancer and vitamin D deficiency.

Dr. Holick: Exactly. And then the key factor that we found was that, as I mentioned to you originally, we realized that the kidney was the major source of the activation of vitamin D. And the function of that is to make activated vitamin D for bone health. But we now also know that the prostate, breast, colon and many other tissues in the body can also activate vitamin D. And by doing so, we think that it locally produces this 125-dihydroxy vitamin D, which then regulates cell growth. It's a cell growth modulator. And I spell all this out in my book "The UV advantage" at www.UVadvantage.com