Adams: It seems like vitamin D is misnamed. It's not really a vitamin in the classic sense, is it?
Dr. Holick: It's a good point, and the reason for it is as follows. It was recognized in the mid-1800s that if you gave cod liver oil to children who had rickets, it could cure rickets. And if you gave cod liver oil to children without rickets, it prevented them from getting rickets. So people thought that there was a vitamin present that was necessary for bone health. And that vitamin was finally identified by taking cod liver oil and boiling it, because once you boil cod liver oil, the vitamin A in it gets destroyed. Originally they thought it was vitamin A that was responsible for bone health, but when they boiled it and destroyed the vitamin A, the anti-ricketic activity, that is the bone health activity, was still present in the cod liver oil. And so it was named vitamin D, because there had already been identified a vitamin A, a B and a C, so the next in line was vitamin D.
Adams: So this was many decades ago then?
Dr. Holick: This was back in the early 1900s. And then they realized that if you're exposed to sunlight, or artificial ultraviolet-B radiation, that it also had anti-ricketic properties, i.e. that it had bone health properties. So all of a sudden people began to appreciate that the vitamin in cod liver oil was also being able to be made by your skin. And so you're correct that it really is not a vitamin, but it's a natural substance that we can make, but we can only make it if we intelligently use sunlight for the purpose of satisfying our body's requirements for vitamin D.
Adams: People don't typically think of their skin as being a pharmaceutical factory, and it's a new concept for a lot of people. Can you explain this point?
Dr. Holick: Yes, in fact the skin is the largest organ in your body, and it's solely responsible for producing vitamin D and providing the body with its vitamin D requirements. And you're quite right that it's basically a factory of all types of chemicals that are being made in the skin, some of which probably alter body functions as well. And certainly one of them is vitamin D.
Adams: I've often heard vitamin D being described as a hormone. Is that a valid description?
Dr. Holick: Well, hormone means it's made in one organ, goes into the blood and has an effect on another organ system. And so if you think about it, since vitamin D is made in the skin and gets into your bloodstream and then goes into the liver and the kidney to get activated, and then goes to the intestines and bones to have its biological effects, by definition vitamin D is a hormone.
Adams: In your research on this, how common is vitamin D deficiency in, say, the American population?
Dr. Holick: What's really remarkable is that vitamin D deficiency is epidemic throughout the entire United States, through all age groups. And I'll give you some examples. It's well known that elders throughout the United States are at high risk. And upwards of 40-60% are at risk for vitamin D deficiency. But we also now realize that even younger adults that are otherwise active and who may be always wearing sunscreen before they go outdoors, or they never see the light of day because they're working all the time. When we did a study in Boston, we found that students and doctors 18-29 years of age, at the end of the winter, 32% were vitamin D deficient.
Adams: Wow.
Dr. Holick: More shocking, though, was that we also looked at young girls (working with Dr Sullivan and Dr Rosen in Maine) -- and these are Caucasian girls ages 9-11 - and we found that 48% were vitamin D deficient at the end of the winter. And 17% remained vitamin D deficient at the end of the summer because of wearing all the sun protection.
Adams: Now that's even more shocking, it's obviously a chronic deficiency.
Dr. Holick: But here's even a bigger shock. I had been concerned, and others had been concerned as well, that if you're not exposed to any sunlight or if you have very deep skin pigmentation, that you need 1000 international units of vitamin D to satisfy your body's requirements. And so we reasoned that probably women during pregnancy, even though they're taking their prenatal vitamins that contain 400 units of vitamin D, they're only getting 40% of what they need. So we did a study at our hospital, and we looked at women coming in and giving birth, and we measured their vitamin D levels -- their 25-hydroxy vitamin D levels, and the infants' 25-hydroxy vitamin D levels at birth. 49 infant-mother pairs were looked at, mostly African-American and Hispanic but some Caucasian as well. 76% of mothers were severely vitamin D deficient. 81% of infants were severely vitamin D deficient.
Adams: That's astonishing.
Dr. Holick: And so, what we're now becoming more concerned about, me and many of the experts, is that infants that are vitamin D deficient at birth can remain vitamin D deficient for the first several months after birth, it may put them at risk of developing many chronic diseases later in life, including type 1 diabetes, rheumatoid arthritis, multiple sclerosis, as well as many of the common cancers of the breast, colon and prostate.
Adams: And this trend - can it be reversed through vitamin D supplementation later on in their life? Or is that set in stone?
Dr. Holick: I don't know. What we're concerned about is the possibility that this may be imprint on the infant for the rest of his/her life. And I'll give you an example. There was a study done in Finland, and what they did was they looked at children 1 year of age that received 2000 units of vitamin D as a supplement for the first several years, and they followed them for over 20 years. And when they compared their risk of getting type 1 diabetes as young adults, they had an 80% reduced risk of developing type 1 diabetes.
Adams: Again, wow.
Dr. Holick: 80% decreased risk! And for children at 1 year of age that were found to have rickets and were vitamin D deficient, they had a fourfold increased risk of getting type-1 diabetes.
Adams: Was there any correlation with adult-onset diabetes as well, or was that not studied?
Dr. Holick: Those studies have not been done, but what we do know is that activated vitamin D does a couple of things. It will regulate insulin secretion by your pancreas, which is of course one of the major problems with type 2 diabetes, and it may increase insulin sensitivity. We think that vitamin D deficiency may exacerbate type 2 diabetes, there's some mounting evidence in the literature to suggest that.
Adams: So, if I can summarize, it appears that we have a nation that is suffering from chronic vitamin D deficiency that we are giving to a whole new generation of children who are starting out deficient and are therefore at a high risk for these diseases.
Dr. Holick: I think so, and that's why we're starting to sound the alarm. I'll give you another statistic. The CDC reported that when they looked across the United States at African American women during their child-bearing years, aged 15-49 years of age, 42% were vitamin D deficient at the end of the winter time.