Adams: It appears that we have a nation suffering from chronic vitamin D deficiency, and that we are creating a whole new generation of children who are starting out deficient and are therefore at a high risk for diseases like diabetes.
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.
Adams: So why isn't this front page news, why aren't Americans being warned right now to go out and get more vitamin D into their bodies?
Dr. Holick: Part of the problem, I believe is that people just take vitamin D for granted. And in fact I've talked to many dermatologists who blithely will say on TV that you just drink another glass of milk, or you get vitamin D from your diet. And unfortunately it's incorrect. They really are ignorant that very few foods naturally contain vitamin D. And we're talking about oily fish like salmon and mackerel, and you would have to eat salmon and mackerel 3-5 times a week in order to get your vitamin D requirement. Cod liver oil is another good source, although milk or orange juice fortified with vitamin D has some, but there are only 100 units in an 8 oz glass of vitamin D-fortified milk and orange juice. So you would have to drink 10 glasses of milk or 10 glasses of orange juice a day. You cannot get your vitamin D easily from your diet. And even if you take a multivitamin, a multivitamin contains 400 international units of vitamin D, only 40% of what you need. So you would have to make a conscious effort to take a multivitamin, drink 2 glasses of milk, drink a glass or two of orange juice fortified with vitamin D and eat salmon to get the amount of vitamin D that you require to satisfy your body.
Adams: Or you could just walk outside and get natural sunlight on your skin.
Dr. Holick: Or you can use sensible sun exposure, right. I mean, we evolved in sunlight. We were bathed in sunlight, we feel better in sunlight. And sunlight provides us with a gift, which is vitamin D. And so, as you're well aware, in my book, I have tables at the end of the book, where I tell people anywhere on the globe, any time of the year, for any skin type at any time of day, how long they can stay outside to get some safe sun to provide them with their vitamin D requirements, and then to use sun protection thereafter.
Adams: I think that's wonderful that you have that kind of chart in your book, because that's what people are wondering. Can you give an example, let's say someone of African descent living in the UK, for example?
Dr. Holick: Sure. If you were living in the UK, say in July, they're much further north than we are in the U.S., about 10 degrees further north in latitude, so the sun's rays are even weaker, so they probably would need a good 30 to 60 minutes of exposure of arms and legs, or hands face and arms, 2-3 times per week.
Adams: So that's several hours a week they need to be getting.
Dr. Holick: Yes. But for a Caucasian it would probably be no more than 5 to 10 minutes.
Adams: Also 2 or 3 times per week?
Dr. Holick: Yes, so it makes a big difference. A typical African American with very deep skin pigmentation -- they have sun protection that's typical of a sun protection factor of 15-30. And what that means is that they can stay out 15-30 times longer. Which means that they need to be out much longer to satisfy their body's requirements of vitamin D.
Adams: Sure, that makes perfect sense.
Dr. Holick: And to give you an example of how powerful putting sunscreen on is, if you put a sunscreen on with an SPF of 8, it reduces your ability to make vitamin D in your skin by more than 95%.
Adams: So you're pretty much shutting down vitamin D production with even a mild sunscreen.
Dr. Holick: Exactly. And so what we recommend is you go outside for 5 or 10 minutes, enjoy the sun, make the vitamin D in your arms and legs or hands face and arms, and then put the sunscreen on.
Adams: Right. That does sound sensible. Is there a direct calculation where you can say X number of minutes under the sun at this latitude equals a certain number of units of vitamin D?
Dr. Holick: Within reason. The problem is that obviously there are clouds in the sky, and there's pollution in the air including ozone which absorbs the vitamin producing rays... but on average, I tell my doctor friends that if you're on the beach on Cape Cod, here in Massachusetts in June, and you know that you're going to get a mild pinkness to your skin, say 30 minutes of being outside, in a bathing suit, it's equivalent to taking 20,000 units of vitamin D orally.
Adams: OK, so that's 20 times more than they might need.
Dr. Holick: Exactly. So what we recommend is that if you just expose 6-10% of your body, a couple of times a week, that's all you need.
Adams: Another question then. Can, in addition to sunburn which is a totally separate issue, can a person's body actually produce too much vitamin D itself where it becomes toxic?
Dr. Holick: The answer is no. The body is very clever and no matter how much sun you're exposed to, you can never become intoxicated with vitamin D. So if you're a sun-worshipper or a lifeguard, there's never been a reported case of vitamin D toxicity. And the reason is, as we had shown many years ago, that when you're exposed to sunlight, your body makes enough vitamin D, and that any excess that's made is destroyed by the sun.
Adams: So it's a self-regulating system, and that's the best way to go.
Dr. Holick: Exactly. And basically it tells you that Mother Nature really had always programmed for you to get your vitamin D requirements from some sensible sun exposure.
Adams: What about storage of vitamin D in the body. If someone lives in a climate where it gets cloudy for 2 months in a row, what then?
Dr. Holick: Excellent point. Remember I told you about the major circulating form of vitamin D which is 25-hydroxy vitamin D? It's half-life in the blood stream is 2 weeks. So when you build up your vitamin D levels during spring, summer and fall, you can use them because your blood levels are much higher, and also some of the vitamin D is stored in your body fat and is released during the winter time. But the opposite is true also, and that is that if you're obese, we know that most obese people are prone to deficiency in vitamin D, and the reason is that the vitamin D gets sucked into the fat and it can't get out. And so we actually did a study in obese and non-obese individuals, and we gave them either an oral dose of vitamin D or we put them on our tanning beds so that they can make vitamin D in their skin. Obese people could only raise their blood levels of vitamin D about half as much as non-obese individuals.
Adams: Very interesting.
Dr. Holick: And so if a person is in fact overweight, they don't need 1000 units of vitamin D a day, they probably need 2000 units of vitamin D a day.
Adams: That's fascinating, because again that plays into the sensitivity to vitamin D, so there's a vicious cycle going on there in obesity.
Dr. Holick: Exactly.
Adams: It's going to take a lot of vitamin D, a lot of sun exposure to help break that cycle. I've got another question for you here. So if a person has all the vitamin D that their body wants, and it's stored in the fat tissues, how long can they go, is it a period of months?
Dr. Holick: Yeah, I mean if you're getting a really adequate source in the spring, summer and fall, it'll last two to three months. So it'll get you through the winter. But for those that are concerned about this issue, what I always tell my patients is, take a multivitamin, you're getting 400 units and get some sun exposure to really make sure that you're building up your stores of vitamin D. And then during the wintertime especially take at least a multivitamin, and maybe take an additional supplement, a vitamin D supplement that contains another 400-1000 units of vitamin D.