SunneD or ShunneD? Vitamin D
Abstract & Commentary
By Russell H. Greenfield, MD, Editor
Synopsis: Regularly offered advice by professionals and the lay media that 5-30 minutes of unprotected daily sun exposure a few days a week is sufficient to maintain adequate vitamin D stores may be misguided and, worse, false, woefully underestimating the amount of sun exposure that may be necessary. Supplementing with appropriate amounts of vitamin D seems the appropriate general course.
Source: Diffey BL. Is casual exposure to summer sunlight effective at maintaining adequate vitamin D status? Photodermatol Photimmunol Photomed 2010;26:172-176.
The author of this piece reconsiders the now mainstream idea that brief sun exposure to uncovered areas of skin such as the hands, arms, and face (about 25% of body surface area) is enough to support healthy stores of vitamin D. Most experts speak in terms of MED, or the minimal erythema dose, as a defined unit of UV exposure; however, MED is not well defined and the standard erythema dose, or SED, is preferable. This is problematic, because the equivalence between terms is unbalanced, with 2-4 SED of sun exposure required for 1 MED in white skin (1 SED is equivalent to approximately one-third of an MED).
The general recommendation for casual sun exposure is further complicated by the fact it does not take into account geographical location (latitude), skin type, seasonal ambient temperature (which may limit the degree of skin exposure), solar UV intensity, the presence of shade or clouds, body positioning (horizontal, vertical, or angled sun exposure), or body geometry. The author offers an example of a person walking randomly under an open sky, finding that the person's average UV exposure is only about 33% of the sun exposure directed to a static horizontal surface; this not even counting the potential impact of shade from trees or buildings, nor even orientation to the sun. Considering that during the week many people are dressed for work and thus have only small areas of the body exposed to the sun at any given time, the author suggests that upwards of 2 hours in an urban environment might be necessary to increase vitamin D levels in any meaningful way, not considering the now widespread topical sunscreen application which would block cutaneous vitamin D production. In addition, the author points out that most of us assume vitamin D production is proportional to exposed body surface, something that may not be true.
The author concludes by stating that trying to improve upon vitamin D status through sun exposure may not be possible without compromising skin health, and that the essential message regarding sun exposure should be avoidance.
Commentary
Why review a review article? Because the message is both interesting and important, and the conclusion flies in the face of conventional "wisdom."
A number of articles focusing on vitamin D's role in health maintenance, how best to assess vitamin D status, and appropriate supplementation have graced the pages of Alternative Medicine Alert in recent months because the research just keeps coming. The other message that just keeps coming is that just a few minutes of unprotected sun exposure to small amounts of your body every few days is sufficient to prevent vitamin D deficiency. Our dermatology peers have not been big fans of this story line and often they have been accused of fear-mongering with regard to skin cancer and premature signs of aging, but this review bears proof that the story line does indeed need to be revisited.
One is left with the realization that a simplistic, linear recommendation has been applied to a problem that is anything but linear. Good science has been used to delineate the equation, to be sure. Numerous studies have been performed that explore the relationship between sun exposure and vitamin D levels, but they generally seem to suffer from, well, generalization. Recommendations for sun exposure to promote adequate vitamin D production need to be individualized and to take into account so many factors that true accuracy seems unattainable. The point may ultimately be moot if, indeed, longer durations of sun exposure might be needed to achieve healthful vitamin D status, durations that would unduly increase the risk of skin damage.
There are other reasons for people to go outdoors, of course, and practitioners should continue to advise so accordingly. But specifically as regards vitamin D and health, it seems clear the emphasis should be on appropriate supplementation and not on unprotected cutaneous sun exposure. Time to buy even more sunblock...
Regularly offered advice by professionals and the lay media that 5-30 minutes of unprotected daily sun exposure a few days a week is sufficient to maintain adequate vitamin D stores may be misguided and, worse, false, woefully underestimating the amount of sun exposure that may be necessary. Supplementing with appropriate amounts of vitamin D seems the appropriate general course.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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