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IRA FLATOW, host:

This is TALK OF THE NATION/SCIENCE FRIDAY. I'm Ira Flatow.

Well, it's a weekend coming up. It's Father's Day. Maybe you bought Dad a backyard grill or a couple of tickets to the ball game. Or maybe you're taking him out to the beach or the lake or someplace where it's going to be really sunny. And we're hoping for sunshine, aren't we? Well, sort of hoping, because remember, you got to bring along that sunscreen. Dermatologists tell you to always wear that sunscreen. But at the recent meeting of the American Association for Cancer Research, an epidemiologist made the provocative suggestion that getting some sun unprotected by sunscreen might actually be good for you because the increased levels of vitamin D created by the sun--You know, sunshine vitamin D?--well, that could help protect against certain cancers.

Joining me now to talk about the idea that some sun may be good for you is Ed Giovannucci, a professor of nutrition and epidemiology at Harvard University's School of Public Health. He's the one that gave the talk at the American Association for Cancer Research meeting.

Welcome to SCIENCE FRIDAY.

Professor ED GIOVANNUCCI (Harvard School of Public Health): I'm glad to be here.

FLATOW: Have you heard all the repercussions yet?

Prof. GIOVANNUCCI: Most of them.

FLATOW: (Laughs)

Prof. GIOVANNUCCI: I guess I opened up a can of worms.

FLATOW: Well, you know, that is--it is, you know, the no--I'm going to say the unwritten rule, but it is the written rule. Go outside, you got to put the sunscreen on. Did you mean not wear any sunscreen and unlimited use of the sun?

Prof. GIOVANNUCCI: Oh, absolutely not.

FLATOW: No.

Prof. GIOVANNUCCI: Yeah. In fact, my talk was really not making the point that necessarily people should go out and get more sun. The context of my talk was that the sun is the main source of vitamin D. And there's a lot of evidence now that indicates that having higher levels of vitamin D is beneficial for cancers as well as other conditions, such as bone fractures, osteoporosis.

FLATOW: So how much time should we be without sunscreen, then?

Prof. GIOVANNUCCI: Well, you know, the question, I think, has to be asked in the context of what our dietary intakes of vitamin D are. The main problem that I have with the current recommendations are not necessarily the avoidance of--you know, avoiding sunburns and excess of sun. But the point is that we recommend about 400 international units of vitamin D. A glass of milk has a hundred units. So four glasses of milk, for example, would give about 400 units.

But the evidence, if you look at--you know, because sun makes a lot more vitamin D than we get from diet, we may need up to about 2,000 units of vitamin D. So we can either get that by getting more sun exposure or by really getting more vitamin D intake.

On the other hand, some people are worried about the toxicity of getting too much vitamin D from their diet. So I--no, my point really is more, I think--I mean, more research needs to be done, but I think we really have to update the intake of vitamin D.

FLATOW: Yeah. It sounds like the Total commercial here. You have to eat so many bowls of Total to get all those vitamins when you could just go out and get some sunshine.

Prof. GIOVANNUCCI: Right, yeah. So I think there's a balance there. I mean, for most people, you know, get some vitamin D from sun and some from diet. But the reality is because diet is really low in vitamin D that most of the vitamin D actually comes from the sun. So until we get the dietary intakes up or put more in supplements, for example, then really the only way we can get close to achieving what I believe are optimal levels of vitamin D is through some sun exposure.

FLATOW: Give us a guideline of what would be the right way to get the sun exposure.

Prof. GIOVANNUCCI: Well, I mean, the--you know, first of all, I totally, you know, support recommendations to avoid, you know, any kind of extreme sun exposure such as that would cause a sunburn. But on the good side, you don't really need a lot of sun exposure to get vitamin D. Like, for--just to give you an example, and I'm not necessarily recommending this, but on the beach on a sunny day, you know, with just a bathing suit on, so you have a lot of your skin exposed, an individual in 20 minutes can make 10,000 to 20,000 units of vitamin D.

FLATOW: Wow.

Prof. GIOVANNUCCI: So in 20 minutes, you make the equivalent of, you know, a hundred to 200 glasses of milk. So, you know, we're really talking almost minutes of exposure here. But many people don't even get that. So, you know, I'm certainly not recommending people going out there and, you know, frying in the sun. And I think it's particularly children, adolescents have to--you know, you have to use caution in how we tell them, you know, about sun exposure. But I think for older adults, I'm not, you know, personally convinced...

FLATOW: Yeah.

Prof. GIOVANNUCCI: ...that five or 10 minutes a day of some sun is a harmful thing.

FLATOW: Yeah. And, you know, in fact, when people put on sunscreen, they don't really put it on the right way to begin with, do they? I mean, they're getting that sun exposure through it anyhow.

Prof. GIOVANNUCCI: That's--there's some truth to that. The sunscreen also, you know, blocks--it's very effective in blocking vitamin D. So if you put on sunscreen, not in an ideal way, you might still get some of the harmful effects of being exposed to the sun, and at the same time you're blocking a lot of the vitamin D production. So that's absolutely correct, yeah.

FLATOW: Does it matter if--you know, we keep hearing that over the years that if you have light skin, you know, if you have skin that easily burns, you shouldn't stay out as long as people who have, you know, dark skin and tan up very easily.

Prof. GIOVANNUCCI: Yes. That actually raises another interesting point in that the--that's why when you asked me, you know, to make a recommendation...

FLATOW: Yeah.

Prof. GIOVANNUCCI: ...the reason I was a little hesitant was that it really varies a lot by a person's skin color and by age, for example. So I think children--I think it's important to, you know, avoid excessive sun exposure, particularly because that may be a risk factor for melanoma, particularly in childhood.

But in terms of avoiding sun exposure, very light-skinned people are very susceptible to skin cancer and to the effects--you know, burning. At the same time, the lighter your skin, the more vitamin D you make. In fact, like the melanin, the pigment in skin, you know, which protects us from sun also in a sense, you know, blocks the ultraviolet from making vitamin D. So a darker-skinned person has lower levels of vitamin D in general. It's particularly a problem in African-Americans that, in general, is a group that is very vitamin D-deficient because the melanin in the skin blocks the production of vitamin D.

So in terms of a guideline that the--it's hard to make, you know...

FLATOW: Yeah.

Prof. GIOVANNUCCI: ...a statement that applies to everybody for all ages.

FLATOW: As a nutritionist, you talked about milk, which is fortified with vitamin D. Are there any foods that naturally have vitamin D in it that we could eat?

Prof. GIOVANNUCCI: Essentially, the only common food that is high in vitamin D is fatty fish. So if you have fish such as salmon--but it has to be a fatty fish, not--you know, like some types of fish are low in fat...

FLATOW: Your omega-3 types.

Prof. GIOVANNUCCI: Exactly. Yeah. Yeah. Yeah. And in fact, as an aside, I wonder--as you know, like, there's some studies that suggest the benefit of omega-3 from fatty fish. And I'm not convinced that vitamin D isn't actually part of that benefit.

FLATOW: Oh, really?

Prof. GIOVANNUCCI: So people eating a lot of fatty fish and getting a lot of omega-3s are also getting a lot of vitamin D. So it is possible that some of the benefit, at least, is from vitamin D. But that's essentially the only food that's high in vitamin D.

FLATOW: And what is the--you know, I think none of us ever think about the benefits of vitamin D. What is vitamin D good for? What kind of benefits does it have?

Prof. GIOVANNUCCI: Well, it's a very interesting story. To make it short, vitamin D has been established to be beneficial for us to absorb calcium. So we hear a lot about getting more calcium in our diets. Actually, I think that message is a little bit off in the sense that while it's important that we get enough calcium, if you don't have enough vitamin D, you don't absorb much of the calcium. And I think more people are probably deficient in vitamin D than are deficient in calcium. So I think--so vitamin D would be--there's studies that prove vitamin D would prevent fractures, at least lower the risk of fractures, osteoporosis. So anything related to bone function, vitamin D is important.

Now that was the classic established function of vitamin D. But in the last 20 years, a wide body of research has suggested many other potential benefits of vitamin D. Now vitamin--every cell, actually, has the capacity--or almost every cell--has the capacity to use vitamin D in different ways. It's almost--you can think of it as a hormone. And when we're deficient in vitamin D, then functions in a lot of different types of cells get affected. And so, for example, vitamin D levels seem to correlate with cell proliferation. So cells that are replicating more rapidly might be at higher risk for cancer. And that's why we believe vitamin D actually may be important against cancer for a wide variety of tissues.

FLATOW: Which kind?

Prof. GIOVANNUCCI: Well, the best evidence to date is for colon cancer, colorectal cancer, which, you know, kills about 50 to 60,000 people in the US every year. There's some evidence for other types of cancers--stomach cancer, esophagus, even breast cancer and prostate cancer. So a lot of cancers have actually been correlated with vitamin D levels or to sun exposure. So we estimate that, you know, as many as--well, we really have to firm this up a bit, but at least there's some evidence that perhaps as many as 20 percent, even 30 percent of cancers, could be related to vitamin D deficiency.

FLATOW: Wow. So you better get your dose of the sun if you want to think about preventing those things.

Prof. GIOVANNUCCI: Well, either the sun or more from diets or supplements.

FLATOW: Maybe they should've had sunlight on that food pyramid that they just came...

Prof. GIOVANNUCCI: (Laughs) Yeah, perhaps. Yeah. You'll really get me in trouble here.

FLATOW: (Laughs) Well, then I'll stop because we've run out of time and you won't have to put your foot in your mouth ...(unintelligible).

(Soundbite of laughter)

Prof. GIOVANNUCCI: OK.

FLATOW: But it was interesting. Thank you for, you know--and I hope the furor, you know, boils down a little for you. So I want to thank you for taking time to talk with us.

Prof. GIOVANNUCCI: No problem.

FLATOW: Ed Giovannucci, who is a professor of nutrition and epidemiology at Harvard University's School of Public Health.

We're going to take a short break and change gears. And when we come back, we're talking about bees. Boy, everything you want to know about bees--I learned a lot reading books of our guests coming up. So if you have bee questions--you know, how to take care of them--did you know that some bees don't have stingers on them? Interesting history of how bees came to this country, brought over by the Europeans, the stinger type. So stay with us. We'll be right back after this short break.

I'm Ira Flatow. This is TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

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