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Oh, That Summer Glow: Healthy or Harmful?

A discussion on the risks and benefits of sun exposure

| From BU Today | By Chris Berdik

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Barbara Gilchrest, a MED professor and former chair of dermatology, and Michael Holick, a School of Medicine professor of medicine, physiology, and biophysics, discuss the risks and benefits of the sun.

Summer’s finally here, and with it the sunshine controversy.

Recent research on the multiple health benefits of vitamin D, stimulated by sun exposure, has led Michael Holick, a School of Medicine professor of medicine, physiology, and biophysics, to argue that many of us could use a few more rays; an overblown fear of sun exposure has exacerbated a common deficiency of vitamin D, he says, which strengthens bones and protects against certain cancers and cardiovascular disease.

But Barbara Gilchrest, a MED professor and former chair of dermatology, points to nearly the 70,000 new cases of melanoma (and more than 8,600 melanoma deaths) every year in the United States. She contends that the public already underapplies sunscreen and that eating more vitamin D–rich food, such as salmon, milk, and fortified cereals, should be enough to cover any “D” deficiencies.

Bostonia asked Gilchrest and Holick to discuss the controversy face-to-face, or at least screen-to-screen, excerpted in the video above. An edited transcript of their longer conversation follows.

Gilchrest: Hello, I’m Barbara Gilchrest, prior chair of the department of dermatology here at Boston University. I’m here with my colleague Mike Holick. Mike?

Holick: I’m Mike Holick, a professor of medicine, physiology, and biophysics, and a former professor of dermatology at Boston University Medical Center.

Gilchrest: We are here this morning to discuss the pseudocontroversy between vitamin D sufficiency and sun exposure. This has been a very contentious topic in the media, of considerable interest to dermatologists, nutritionists, and endocrinologists. We have several specific questions frequently asked by the media and by our patients, and Mike and I would like to try to explain them. The first question that has been posed is, what is sensible sun exposure? Would you like to respond to that, Mike?

Holick: Humans evolved in sunlight, and we’ve always depended on the sun for our vitamin D requirement, because you can’t get it all from your diet. I’ve always recommended sensible sun exposure, which is maybe no more than 5 to 10 minutes on arms and legs, a couple of times a week, here in Boston from about mid-April until about mid-September, followed by good sun protection, and always wearing sun protection on your face.

Gilchrest: I would completely agree with that recommendation. The difficulty has been that this safe sun exposure message has been heard by many teenagers and young adults as let’s go to the beach all day without sunscreen. It has also suggested to many people that safe sun practices will prohibit them from having an adequate vitamin D level. A few minutes a day, several times a week, of unprotected sun exposure on limited parts of the body is completely reasonable, but it’s not what we see young people doing at the beach.

Holick: I agree. But as you know, young people have been doing this forever. Back in the ’60s and ’70s they were out there putting baby oil on.

Gilchrest: Which is exactly why we have an epidemic of skin cancer, more than a million cases a year in this country. In addition, essentially everyone by middle age in this society has unattractive photoaging changes in their skin. You mentioned how we evolved in sunlight, and that’s certainly true. Nature set up a wonderful system for people who are going to be dead by age 40. But today most people are living into their 70s and 80s and 90s, and it is those individuals who enjoyed unlimited sun exposure in their youth who are having such terrible problems with chronic sun damage and skin cancer.

And although I am aware that you and others are concerned that many people have less than optimal vitamin D levels, we have a pretty healthy developed world. People are living into their 80s on average. These are healthy people, and there’s no shortage of the next generation. So it would seem that we are managing to get adequate vitamin D from the combination of sun exposure and diet, and supplements, which are used by many individuals, particularly if they are concerned about their vitamin D sufficiency.

Holick: The problem with that concept is that more than 50 percent of the world’s population is vitamin D–deficient. And last year, we showed that even among healthy adults in Boston, essentially 100 percent were vitamin D–deficient.

Gilchrest: There’s a problem with your definition of deficiency. It has classically meant a state in which there is an illness, where there is a health problem that is correctable by giving additional vitamin D. I cannot accept your statement that 100 percent of the population is vitamin D–deficient. You mean that their 25 hydroxy vitamin D levels during the winter fall below what you and some others would consider to be optimal levels?

Holick: No. What we’re saying is that your body responds by removing calcium from your skeleton if you don’t have a blood level of vitamin D at least 20 nanograms per milliliter. Anything less than that is considered to be vitamin D deficiency.

Gilchrest: So it is your opinion that 100 percent of people in Boston during the winter have a disease that would be correctable by vitamin D supplements?

Holick: What we’re saying is that they have an increase in parathyroid hormone levels, and as a result, they’re stealing calcium out of their skeletons because they can’t efficiently absorb the calcium they get from their diet due to insufficient vitamin D. And so yes, that’s why even young and middle-aged adults lose an average of about a quarter to half a percent of their bone mass per year. If you had adequate calcium and vitamin D on board, you would prevent that.

Gilchrest: Perhaps we should move along to question number two, which is: have Americans gone overboard when it comes to protecting themselves from the sun?

Holick: A lot of the dermatologists had been advocating abstinence from direct sun exposure. I think that’s put people at risk for vitamin D deficiency. We showed that under controlled conditions, if you put on sunscreen with the sun protection factor of 30, you reduce your ability to make vitamin D in your skin by as much as 99 percent. We showed in a group of farmers that when they wore sunscreen all the time, by the end of the winter, being outside all the time, essentially all of them were vitamin D–deficient. So I think that unprotected sun exposure like we had talked about before — 15 minutes a couple of times a week on arms and legs — is not unreasonable, followed by good sun protection. But I don’t think suggesting abstinence from any direct sun exposure is a healthy recommendation.

Gilchrest: I think you’re somewhat overstating the position of the American Academy of Dermatology. Nobody, no healthy individual, is abstinent from sun exposure. We are not talking here about very elderly or very unhealthy individuals. We’re talking about healthy teenagers and young adults who are outdoors every day. They probably have a good hour on average of exposure, hopefully protected by sunscreen, and that will certainly allow them the equivalent of your unprotected sun exposure 5 to 10 or 15 minutes a day. You get that sun exposure through your sunscreen. While it is possible to use an SPF 30 sunscreen as requested by the manufacturer to block 97 percent of the UV energy that causes cancer and causes vitamin D production, most people don’t use their sunscreens that way. It’s well established that almost everyone applies their sunscreen in a manner that permits much, much more transmission of UV, on average probably 80 percent protection rather than 97 percent protection, even with the very high SPF sunscreen. So I just can’t accept your suggestion that wearing a sunscreen prevents vitamin D production or, alas, prevents chronic sun damage.

Holick: Again, putting it into perspective, the American Academy of Dermatology in November of last year came out with a physician statement arguing that you should never be exposed to direct sunlight without some protection. They urged people worried about their vitamin D requirement to get it from their diet or a supplement, which of course is unrealistic.

Gilchrest: Excuse me, Mike — a supplement is unrealistic?

Holick: It’s unrealistic to think that you’re going to get every child and adult in the United States to take a vitamin D supplement every day. And so putting things in perspective again, teenagers are at high risk for vitamin D deficiency. Researchers showed at Children’s Hospital that more than 50 percent of teenagers are vitamin D–deficient throughout the year in Boston. It’s been demonstrated that teenagers who are vitamin D–deficient have more than double the risk of developing high blood pressure, high blood sugar …

Gilchrest: I think we’ve covered the fact that vitamin D is important and that you can take a vitamin D supplement. CVS sells 1,000 international units for five cents per capsule, which I think most people would feel is highly adequate, even if you are avoiding sun.

Holick: Actually it’s not.

Gilchrest: It’s not?

Holick: In a study last year, we showed that among healthy young and middle-aged Bostonians getting 1,000 units of vitamin D a day, not one person was vitamin D sufficient, meaning a blood level of greater than 30 nanograms per milliliter, which is important for reducing risk of common cancers, autoimmune diseases, infectious diseases, etc.

Gilchrest: There’s a lot of debate not only among dermatologists, nutritionists, nephrologists, and endocrinologists about what constitutes a healthy level of vitamin D.

Holick: I don’t think that’s quite true, Barbara. The National Kidney Foundation guidelines specifically say that all patients with kidney disease have to have a blood level of 25 hydroxy vitamin D above 30 nanograms per milliliter.

Gilchrest: Not everyone has kidney disease. We’re talking here about healthy young people. I have spoken with nephrologists at meetings and a vitamin D workshop, and there was a lot of concern that pushing everyone’s vitamin D level sky high with supplements or sun exposure or whatever might increase the risk of kidney stones.

Holick: A little knowledge is a dangerous thing, and a lot of nephrologists, unfortunately are in that position. It’s the National Kidney Foundation, the expert nephrologists, telling their nephrologists to get the blood levels of vitamin D above 30 nanograms per milliliter. There is no evidence that you increase the risk of kidney stones by increasing your vitamin D intake, contrary to popular belief.

Gilchrest: There has been an increased incidence of kidney stones in some published studies in which vitamin D supplementation was used to increase vitamin D levels.

Holick: That was only in the Women’s Health Initiative, and if you read that study carefully, they did not control the calcium intake in those women. Those women were taking up to two grams of calcium a day, which would put them at increased risk for kidney stones, not the vitamin D. They were only on 400 units of that a day.

Gilchrest: Clearly this is a very passionate topic for us. The next question is …

Holick: But I don’t think we really discussed the importance of vitamin D for health. We know that it’s important for preventing rickets in children. What young and middle-aged adults don’t realize is that a lot of the aches and pains in their bones and muscles by the end of the winter are caused by vitamin D deficiency. And as you’re well aware, a lot of epidemiologic studies have related vitamin D deficiency with increased risk of common cancers and autoimmune diseases, and even infectious diseases.

Gilchrest: Unfortunately, they are all confounded by lifestyle variables, such as obesity and many other factors, Mike — you know that.

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