According to the website, Cancer Research UK, it states that “using sunbeds can increase your risk of melanoma skin cancer by 16-20%”.1
In support of this statement, a meta-analysis of observational studies in 2014 of those with melanoma who had used indoor tanning beds (sunbeds), found that the odds ratio for melanoma associated with “ever use” of sunbeds was 1.16.2 In other words, there was a 16% increase in the odds of getting a melanoma with sunbed use compared to not using a sunbed. However, the authors conceded that the quality of the evidence contributing to their analysis ranged from poor to mediocre and the acknowledged a recognised limitation of observational studies, namely recall bias. In contrast, a meta-analysis of observational studies in 2018 was less circumspect and concluded that scientific knowledge [on the link between indoor tanning and melanoma] is mainly based on poor quality data and that there is currently no convincing evidence that moderate/responsible use of solarium (indoor tanning) increases melanoma risk.3
The problem with analysing observational studies is that they can only demonstrate that the two factors, in this case sunbed use and melanoma, are associated: it is impossible to prove causality, that is, that sunbed use leads to melanoma. The fallacy of relying upon observational studies to “prove” that associations are causally related was most clearly highlighted with the use of hormone replacement therapy (HRT). Meta-analysis of observational studies clearly showed that HRT had cardio-protective effects,4 yet when randomised controlled trials (that is, the gold standard) were undertaken, there were no cardiovascular benefits from HRT.5
In the most recent review on sunbed use and the association with melanoma, published in January 2020, yet another article was critical of the available evidence.6 A key argument made in the latest analysis is that individuals who use sunbeds are effectively “sun-worshippers” that indulge in sun risk behaviours and that trying to untangle the effects of over-exposure to sunlight and the use of sunbeds is extremely difficult. In support of their argument, a recent study of the characteristics of sunbed users described a typical user as a young adult female, who also smoked and engaged in sun-seeking behaviours (for example, sunny holidays and sunburn).7 Further support for the notion that it is over-exposure to sunlight rather than sunbed use that leads to melanoma comes from a recent French study. The authors found that 83% of melanomas were due to exposure to UV radiation and only 1.5 % (for men) and 4.6% (for women) are due to use of sunbeds.8 Furthermore, in an analysis of the factors associated with the development of a second melanoma, Austrian researchers found that both outdoor occupation and solarium (sunbed) use did not increase the risk of a subsequent melanoma.9
Although meta-analyses generally report an odds ratio of around 1.2 for the relationship between sunbed use and melanoma, is this something to be worried about? In order to provide some context, it has been suggested that an odds ratio of 1.68 represents a “weak association” between two factors, whereas an odds ratio of 6.71 represents a strong association10 hence an odds ratio of 1.2 is a very weak association. Furthermore, public health campaigns to warn about the dangers of sunbed use would appear to go unheeded. In a recent European study in 30 countries including over 227,000 individuals, the overall prevalence of sunbed use was found to be 10.6% with a higher prevalence in younger females.11 Fortunately, other work has shown that the introduction of regulations on the use of sunbed has been found to lead to a 70% drop in teenage use of sunbeds.12
While legislation can help to regulate who uses a sunbed, public health campaigns warning of the dangers are being potentially undermined when bodies such as the World Health Organization (WHO) say that “few studies have been undertaken to systematically assess the dangers of sunbed use, and the picture remains equivocal … due to the long latency period for skin cancer and eye damage it has been difficult so far to demonstrate any long-term health effects.”13
With research describing how use of sunbeds is driven by aesthetic needs,7 getting a pre-holiday tan and modelling parental behaviours, it would seem that public health campaigns need to focus not solely on the harms associated with sunbed use but to emphasise that the short-term cosmetic benefits from a sunbed may result in a higher price in later life. With the absence of definitive proof that sunbed use increases the risk of developing a melanoma, it would still be folly to suggest otherwise.
References
1. Cancer Research UK. How do sunbeds cause skin cancer? www.cancerresearchuk.org/about-cancer/causes-of-cancer/sun-uv-and-cancer/how-do-sunbeds-cause-skin-cancer (accessed January 2020).
2. Colantonio S, Bracken MB, Beecker J. The association of indoor tanning and melanoma in adults: systemic review and meta-analysis. J Am Acad Dermatol 2014;70:847–57.
3. Burgard B et al. Solarium use and risk of malignant melanoma: meta-analysis and evidence-based medicine systematic review. Anticancer Res 2018;38(2):1187–99.
4. Stampfer MJ, Colditz GA. Estrogen replacement therapy and coronary heart disease: a quantitative assessment of the epidemiological evidence. 2004;33:445–53.
5. Hulley S et al. Randomised trial of oestrogen plus progestin for secondary prevention of coronary heart disease in postmenopausal women. Heart and Estrogen/progesin replacement study (HERS) research group. JAMA 1998;280(7):605–13.
6. Reichrath J et al. Sunbeds and melanoma risk: many questions open questions, not yet time to close the debate. Anticancer Res 2020;40(1):501–9.
7. Suppa M et al. Who, why where: an overview of determinants of sunbed use in Europe. J Eur Acad Dermatol Venereol 2019;33(Suppl 2):6–12.
8. Arnold M et al. Cutaneous melanomas in France in 2015 attributable to solar ultraviolet radiation and the use of sunbeds. J Eur Acad Dermatol Venereol 2018;32(10):1681–6.
9. Miller C et al. Risk factors of subsequent primary melanomas in Austria. JAMA Dermatol 2019;155(2):188–95.
10. Chen H, Cohen P, Chen S. How big is a big odds ratio? Interpreting the magnitude of odds ratios in epidemiological studies. Commun Stat-simul C 2010;39(4):860–4.
11. Suppa M et al. Prevalence and determinants of sunbed use in thirty European countries: data from the Euromelanoma skin cancer prevention campaign. J Eur Acad Dermatol Venereol 2019;33(Suppl 2):13–27.
12. Rodriguez-Acevedo AJ et al. Indoor tanning prevalence after the international agency for research on cancer statement on carcinogenicity of artificial tanning devices: a systematic review and meta-analysis. Br J Dermatol 2019;5 Aug [Epub ahead of print].
13. World Health Organisation. What are the risks from sunbed use? www.who.int/uv/faq/sunbeds/en/index4.html (accessed January 2020).
