Timing of excessive ultraviolet radiation and melanoma: epidemiology does not support the existence of a critical period of high susceptibility to solar ultraviolet radiation- induced melanoma

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Abstract
Background The existence of a ‘critical period’ early in life characterized by a high susceptibility to melanoma initiation due to excessive ultraviolet (UV) radiation has been suggested by various authors based on epidemiological findings from migration studies and some case–control studies. However, the evidence so far is controversial as several epidemiological investigations failed to corroborate these results. Objective To compare the increase in melanoma risk due to excessive UV radiation between different periods in life. Methods In a multicentre case–control study we recruited 603 melanoma cases and 627 population controls in seven European countries. We obtained data on the history of sunburns during ‘childhood’ (≤ 15 years) and ‘adulthood’ (> 15 years), respectively, in standardized personal interviews. We employed logistic regression analyses to estimate the impact of the exposure factors under study, while simultaneously controlling for the effect of a variety of confounding variables. Results We found a very similar upward gradient of melanoma risk in exposure categories related to the frequency of sunburns during both periods in life. More than five sunburns doubled the melanoma risk, irrespective of their timing in life. Conclusions Our data do not provide supporting evidence for the existence of a ‘critical period’. The hazardous impact of sunburns seems to persist lifelong and thus activities concerned with melanoma prevention should be directed to the entire population rather than being focused only on younger age groups.