Tanning Beds and Cancer Risk
Like watching a good movie, I laughed and I cried when I read a recent editorial published in a college newspaper by the manager of a tanning salon extolling the virtues of indoor tanning (
http://breezejmu.org/2009/09/03/some-sunny-perspective/). I thought it deserved a professional response.
The tanning bed manager's main issue is a recent classification by the IARC (International Agency for Research on Cancer) classifying UV-emitting tanning devices as carcinogenic to humans. She calls the report an over-the-top, ridiculous suggestion that getting a suntan is in the same risk category as cigarettes, arsenic and plutonium. She then goes on to say that "not one single study exists anywhere in the world implicating tanning in a non-burning fashion as a significant risk factor for permanent skin damage."
The first thing to know is that the various classification groupings of the IARC simply relate to an evaluation of carcinogenic risk. UV-emitting tanning devices have been moved from Group 2A up to Group 1, meaning that the agent is unquestionably carginogenic to humans. Group 2A means the agent is probably carcinogenic to humans. Group 1 includes solar radiation, as sun exposure is a known cause of skin cancer including basal cell carcinoma, squamous cell carcinoma, and malignant melanoma. The classification system does not delineate as to types or grades of cancer produced. So tanning should be in the same category as smoking and arsenic. They are all carcinogenic. Period.
The decision was based on a comprehensive meta-analysis of roughly 20 epidemiological studies from peer-reviewed publications showing sufficient evidence that the risk of cutaneous melanoma is increased with tanning bed use. The term "sufficient evidence" is used because the studies, although valid in their conclusions, were not randomized, controlled trials, which is considered the gold standard in medical research. That would entail taking a group of people and exposing them to a harmful condition, knowing it is most likely harmful, just to prove the point. This has not been allowed since the World Medical Association developed the Declaration of Helsinki as a statement of ethical principles for all medical research, meaning that medical research has the duty to protect and promote the safety and health of all human subjects. Another example of this would be taking a cohort of pregnant women and having them take a drug that is thought to cause birth defects just to prove that it really does. It is just not going to happen; but it makes the conclusions drawn from evaluating the outcome of people who have been exposed to the agent no less valid.
The tanning bed manager writes "The sum of data do not substantively link indoor tanning equipment with an increased risk of melanoma. Indeed according to the IARC, 18 of 22 epidemiological studies ever conducted on this topic show no significant association." Her argument here is partially correct. Eighteen of the examined studies were not statistically significant on their own, but they trended toward an increase in certain types of skin cancer among tanning bed users. There are many reasons why individual studies may not be statistically significant and most are based on inherent limitations in performing retrospective analyses. This is the whole point to performing a comprehensive meta-analysis. By combining well-designed smaller studies into one large data pool, the power of the study is increased and the results may become more significant.
The IARC classification statement as well as the original meta-analysis states that based on 19 informative studies, "ever-use of sunbeds was positively associated with melanoma", detailing a 1.15 relative risk with a statistically significant 95% confidence interval. The IARC analysis also goes on to say that there is no consistent evidence of a dose-response relationship, meaning it doesn't matter if you tan in a tanning bed once in a while or on a regular basis, your risk for melanoma is increased by simply by using a tanning bed. The review confirms having first exposure to a tanning bed before the age of 35 can increase your risk of melanoma by as much as 75% (again, they cite a statistically significant 95% confidence interval here with a relative risk of 1.75). Incidentally, the report did say that they found no evidence to support a protective effect of the use of sunbeds against damage to the skin from subsequent sun exposure. So any of you who use a tanning bed to get a "base tan" for the summer or vacation, forget it.
The tanning bed manager then writes that the relationship between melanoma and sunlight cannot possibly be clear-cut because indoor office workers are more likely to get melanoma than those who work outdoors. The tanning bed manager is again partially correct in her statement, but the issue is much broader. Melanoma is a complex disease that often results from a combination of factors, rather than a single cause. These include genetics (i.e. fair skin, family history, the presence of dysplastic moles), environmental factors (i.e. history of sunburn, excessive sun exposure, exposure to carcinogens- including arsenic compounds), a weakened immune system (i.e. organ transplant patients, chronic leukemias or other cancers, medications), and lifestyle decisions (i.e. living in a sunny climate, tanning). She is also correct in stating that studies have shown office workers do have an elevated risk of melanoma compared to outdoor workers (Lee & Strickland 1980), however the increased risk is limited to professional and administrative type workers, not indoor workers as a whole. The discrepancy is thought to be tied to the professional workers having a higher socioecomonic status as they are the ones who work all year and earn enough money to go on a blowout beach vacation (only to come back with a sunburn). Studies also show outdoor workers do have an increased risk of melanoma, interestingly enough on the sun-exposed parts of their bodies versus the parts covered by protective clothing (Beral and Robinson 1981; Vagero et al. 1986).
Finally, the tanning bed manager calls the use of ultraviolet therapy by dermatology professionals to treat "psoriasis and other purely cosmetic disorders" hypocrisy. This statement just made me sad. I am guessing that the tanning bed manager does not have psoriasis or any friends or family members with severe psoriasis. If she did, she would never call it a purely cosmetic disorder. Psoriasis is a complex systemic disease that can have a significant negative impact on a patient's overall quality of life including their job and relationships. When dermatologists use light box therapy, they are generally treating patients with severe disease that is unresponsive or uncontrolled by other methods. The gold standard for light therapy is narrowband UVB, which does not pose significant risks for skin cancer in later life if used appropriately.
The bottom line is that sources of ultraviolet radiation, whether from the sun or a tanning bed, do emit ionizing radiation that causes specific mutations in the users DNA that can lead to skin cancers, not to mention wrinkled, saggy skin. The change in classification will probably not be enough to convince hard-core tanners to abandon their bronzing, but I suspect it may lead to government regulation such as banning under-18s from using sunbeds, required warnings to customers about the risks of sunbeds, and tighter supervision.
Further Reading:
- Beral V, Robinson N. The relationship of malignant melanoma, basal and squamous skin cancers to indoor and outdoor work. Br J Cancer. 44:886-91, 1981.
- El Ghissassi F, Baan R, Straif K, et al. on behalf of the WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens-Part D: radiation. The Lancet Oncology. 10:751-2, 2009.
- IARC Working Group, The association of use of sunbeds with cutaneous malignant melanoma and other skin cancers: a systematic review. Int J Cancer. 120:116-22, 2006.
- Lee JAH, Strickland D. Malignant melanoma: Social status and outdoor work. Br J Cancer. 41:757-63, 1980.
- Vagero D, Ringback G, Kiviranta H. Melanoma and other tumours of the skin among office, other indoor and outdoor workers in Sweden 1961-1979. Br J Cancer 53:507-12, 1986.