No proof sunscreens prevent cancer
Posted by medconsumers on February 13, 2011
“Sunscreens protect against sunburn, but there’s no evidence that they protect against basal cell carcinoma or melanoma.”… “Death from skin cancer is advertised as being avoidable with the use of sunscreens. This position might actually be true, but there is as yet absolutely no scientific evidence to support it.”
We should all be grateful to the researcher I just quoted: Marianne Berwick, PhD, MPH, University of New Mexico, Albuquerque. For many years, Dr. Berwick has been calling attention to the information gap behind the sunscreens-prevent-cancer message to the public. As the Division Chief & Head of Cancer Epidemiology & Prevention at UNM, she has co-authored over a hundred research papers about skin cancer. In a new commentary for Clinical Pharmacology & Therapeutics, she is asking, once again, the research question that all dermatologists should be asking: Where’s the proof?
Dr. Berwick singled out two exceptions to the information gap: There is some evidence that sunscreens can reduce the prevalence of recurrent squamous cell carcinoma (SCC) and actinic keratosis (AK), the small pre-cancerous rough spots on skin. Both are related to sun exposure—periodic severe sunburns in childhood for SCC and chronic sun exposure in the case of AK. As for melanoma, Dr. Berwick’s earlier research raised questions about the medical certainty that this deadliest of all skin cancers is primarily due to sun exposure. In 2005, she co-authored a study that came to this counterintuitive conclusion: “Sun exposure is associated with increased survival from melanoma.”
Why, I asked Dr. Berwick, aren’t the dermatologists calling for more research? After all, sunscreens are central to their prevention message (right up there with clothing, hats, and heading for the shade). “Dermatologists have not clamored for answers regarding cancer prevention and sunscreens as most clinicians (but not all) are trained to care for patients and not to conduct research. The idea that sunscreens prevent sunburn, which they do admirably well, and that sunburns are strongly associated with risk for skin cancer of all types, leads many to make the connection that ‘thus sunscreens prevent skin cancer’. Only when we understand the mechanism by which skin cancers develop will we be able to make such claims,” answered Dr. Berwick, in an e-mail.
Over the last decade, increased vitamin D intake has begun to loom large as a way to prevent everything from colon cancer to autoimmune disorders. But some worry that religiously applying sunscreen might inhibit the skin’s ability to turn sunlight exposure into vitamin D. And perhaps sunscreen use merely trades the prevention of skin cancers for an increased risk for something worse, like multiple sclerosis. But vitamin D researchers contend that even fair skinned people don’t require very much exposure to sunlight to make adequate amounts of vitamin D. Besides, as Dr. Berwick points out in her commentary, studies show that most people don’t apply sunscreen in the recommended amount or reapply it as frequently as recommended.
You might think, “Well, sunscreens can’t hurt, so I’ll keep on applying the sunscreen to avoid sunburn and wrinkles.” But Dr. Berwick says, “There are major concerns about the safety of the major chemicals used, even avobenzone (Parsol 1789) and ecamsule (Mexoryl SX), which are considered safe by the Environmental Working Group.” Click here
With so many unanswered questions, why doesn’t the federal government sponsor the badly needed sunscreen research? “The reason National Cancer Institute has not put money into research on skin cancer is probably the same reason that most of NCI money goes to trying to cure advanced cancer; possibly there is more advocacy for cure than prevention. Prevention really has not gained a strong foothold at NCI, but you never know…maybe soon,” answered Dr. Berwick, who added her own hunch. “I have the unsubstantiated feeling that most people think skin cancer is not a problem. However (according to the American Cancer Society), more people die from melanoma each year (8,700) as die from cervical cancer (4,210), endometrial cancer (7,950), oral cancer (7,880), laryngeal cancer (3,600), acute lymphocytic leukemia(1,420), chronic lymphocytic leukemia (4,390) and similar to acute myeloid leukemia (8,950), so surely that is a problem.”
For more information:
After Dr. Berwick published this commentary, positive results from a “randomized” study of sunscreen and melanoma were published in the Journal of Clinical Oncology by Dr. Adele Green and her colleagues. This study does give some evidence that sunscreens might prevent melanoma, but Dr. Berwick thinks that “the study has many problems and would not consider it proof (yet).” To read the abstract, click here.
Maryann Napoli, Center for Medical Consumers©