By Abby S. Van Voorhees, MD, December 02, 2013
In this month’s Acta Eruditorum column, Physician Editor Abby S. Van Voorhees, MD, talks with Adele Green, MB BS, PhD, MSc, about her recent Annals of Internal Medicine article, “Sunscreen and Prevention of Skin Aging.”
Dr. Van Voorhees: Getting patients to use sunscreens is always a challenge and the fear of possible skin cancer is often not enough to get people to protect their skin in the sun. When I saw your paper about the potential role of sunscreens in the prevention of aging of the skin it caught my attention since most patients truly care about how their skin looks. What has been known up until this point?
Green: It has long been known that most skin aging changes are due to photoaging after cumulative sun exposure, superimposed on chronological aging. Many topical anti-aging agents have been promoted as being efficacious, including sunscreen, but there was no evidence that sunscreen can actually protect against skin aging apart from in experimental animals.
Dr. Van Voorhees: Many people believe that beta carotene has photoprotective properties. Is this why you studied this agent as well? How strong was the prior literature demonstrating its effectiveness at preventing photoaging? [pagebreak]
Green: Again, there had been only experimental evidence [in animals] that oral antioxidants can reduce signs of oxidative skin damage and wrinkling due to sun exposure; there was no strong evidence that this applied to humans. At the time we started this trial, epidemiological evidence suggested that people whose diets were rich in beta-carotene were less likely to develop certain epithelial cancers. Putting both of these together, we wished to test the hypothesis that the antioxidant properties of beta carotene protected against both the development of skin cancer and the progression of photoaging.
Dr. Van Voorhees: Tell us about your study design. How were patients randomized to the various study groups? Where there any differences in the amount of sun exposure that the various groups received over the time that this was being studied?
Green: Participants were not patients of a clinic; rather, they were randomly selected adult residents of the Queensland, Australia, township of Nambour aged under 55. Using a computer-generated randomized list, they were allocated to daily application of sunscreen labeled Sun Protection Factor (SPF) 15+ and broad-spectrum or discretionary sunscreen use (placebo sunscreen was considered unethical); and independently, to 30mg beta-carotene or placebo supplements daily. Those allocated to daily sunscreen were asked to apply the intervention sunscreen to head, neck, arms, and hands every morning, with reapplication after heavy sweating, bathing, or spending more than a few hours outdoors while the control group were not given any instructions regarding sunscreen use. [pagebreak]
Reported sun exposure was similar between the daily and discretionary sunscreen groups during the trial (around three-quarters of both groups spent less than 50 percent of weekend time outdoors) and use of other sun protection measures like seeking shade and wearing a hat was almost the same in both treatment groups.
Dr. Van Voorhees: What did you find as a consequence of your investigation? Did either sunscreens or beta carotene demonstrate benefit in the prevention of photoaging? Was there a difference if sunscreens were used daily versus more intermittently?
Green: The group that were allocated to using sunscreen regularly showed 24 percent less photoaging than the group who used sunscreen only some of the time if at all; in fact the sunscreen group showed no detectable increase in aging during the trial period. (The trial was analyzed according to treatment allocation to preserve the balance of confounding factors achieved by randomization, rather than according to amount of sunscreen used, when one would lose the benefits of random allocation.) Beta-carotene supplementation had no effect on skin aging overall, though we saw contrasting associations in those with less severe versus more severe aging at baseline. [pagebreak]
Dr. Van Voorhees: How frequently did the daily sunscreen users really use their sunscreen and how can you be sure that they truly did? Were you able to control for factors such as smoking or other risks which we know will damage the skin? How about the exact ingredients of the sun screen or its sun protection rating — did this matter?
Green: By the end of the trial 77 percent of daily sunscreen users were applying sunscreen at least three to four days a week compared with 33 percent of discretionary users. Every three months adherence to the sunscreen protocol was assessed by measured weights of returned sunscreen bottles (intervention group). We were able to control for factors such as smoking or other risk factors that damage the skin purely by the randomization, meaning that equal proportions of people in the treatment groups were exposed to these factors.
Whether our results would have differed with a higher SPF sunscreen (15+ was all that was available when the trial commenced) or one with greater absorption in the UVA spectrum is debatable, since the factor of overriding importance is the application of a liberal quantity of sunscreen and the SPF or precise shape of the sunscreen-absorption spectrum is much less important. [pagebreak]
Dr. Van Voorhees: I’m sure that you have read the recent paper in JAMA Dermatology by Steve Feldman’s group reporting that physicians are actually less dutiful about reminding patients to use sunscreens than we believe about ourselves. That paper suggests that dermatologists tell patients to use sunscreen only 1.6 percent of the time. Do you think that your study may help convince all of us to redouble our educational efforts in this regard?
Green: We’ve shown that regular sunscreen use by young and mid-aged adults under 55 brings cosmetic benefits, while decreasing their risk of skin cancer in the long-term, so my hope is that these results will enable dermatologists to tell patients about the cosmetic benefit of sunscreen and other sun protection. The flip side is that not being sun-safe will have a negative effect on their appearance as well as raising their chances of developing skin cancer.