Abstract
Aim A melanoma case-control study was conducted to elucidate the complex relationship between sun exposure and risk. Methods Nine hundred and sixty population-ascertained cases, 513 population and 174 sibling controls recruited in England provided detailed sun exposure and phenotype data; a subset provided serum 25-hydroxyvitamin D 2 + D 3 levels. Results Phenotypes associated with a tendency to sunburn and reported sunburn at ⩾20 years of age were associated with increased melanoma risk (odds ratio (OR) 1.56, 95% confidence intervals (CI) 1.23–1.99). Holiday sun exposure was not associated with an increased melanoma risk although this may be in part because reported sun exposure overall was much lower in those with a sun-sensitive phenotype, particularly among controls. Head and neck melanoma was associated with less sun exposure on holidays at low latitudes (OR 0.39, 95% CI (0.23–0.68) for >13 h/year compared to <3.1). Overall the clearest relationship between reported sun exposure and risk was for average weekend sun exposure in warmer months, which was protective (OR 0.67, 95% CI 0.50–0.89 for highest versus lowest tertile of exposure). Serum vitamin D levels were strongly associated with increased weekend and holiday sun exposure. Conclusions Sun-sensitive phenotypes and reported sunburn were associated with an increased risk of melanoma. Although no evidence was seen of a causal relationship between holiday sun exposure and increased risk, this is consistent with the view that intense sun exposure is causal for melanoma in those prone to sunburn. A protective effect of regular weekend sun exposure was seen, particularly for limb tumours, which could be mediated by photoadaptation or higher vitamin D levels.
Highlights
Many case-control studies have established phenotypic and behavioural risk factors for melanoma in populations of European origin, summarised in meta-analyses [1,2,3]
Sun-sensitive phenotypes and reported sunburn were associated with an increased risk of melanoma
No evidence was seen of a causal relationship between holiday sun exposure and increased risk, this is consistent with the view that intense sun exposure is causal for melanoma in those prone to sunburn
Summary
Many case-control studies have established phenotypic and behavioural risk factors for melanoma in populations of European origin, summarised in meta-analyses [1,2,3]. The relationship between sun exposure and risk is thought to be complex: for example some studies have suggested that occupational sun exposure might be protective for melanoma [2]. Hypotheses developed to explain this apparent anomaly are that continuous sun exposure (not associated with severe sunburn) might be protective for melanoma either by inducing photoadaption (increased melanisation and epidermal thickening)(5) or as a result of the induction of higher levels of vitamin D. There was no evidence in a recently published cohort study of a protective effect of reported greater vitamin D intake on melanoma risk [8] for example, but there are genetic data to suggest that inherited variation in the vitamin D receptor (VDR) gene is associated with melanoma risk, recently published in meta-analyses [9]
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